oil and soap experiment

Oil and Water Experiment: Simple Science for Kids

A fun and simple science experiment for kids using just 3 common household items.

Experimenting with oil,water and dishwashing detergent is a fun way to explore basic chemistry with kids.

This science experiment is suitable for kids over 4 years of age.

There is no need any special equipment… in fact I am sure you already have everything you need in your kitchen cupboards. It can be a little messy so I suggest attempting the experiment outside or somewhere that is easy to clean.

When my kids and I are playing with science I like to ask them lots of questions and listen to their answers – they come up with some very imaginative responses. But if you are interested in the facts, I have included an explanation for what is happening at the end of the post.

Oil, Water & Detergent Experiment

You will need:

• Glass jam jars (with secure lids if you want to shake them)
• Jug of water
• Vegetable oil
• Dishwashing detergent
• Food colouring
• Small container
• Syringes or pipettes
• A cloth for accidental spills
• Optional: Table salt

Experiment Directions: 1. Pour one cup of water into your glass jam jar.

2. Pour half a cup of vegetable oil on top of the water in the jar.

3. Stop and observe. Does the oil mix with the water? Screw the lid onto the jar and shake it…. can you make the oil and water  mix?

For children learning about density this is a great time to ask, “Is the vegetable oil more or less dense than the water?”

4. Mix a generous squirt of dishwashing detergent with some food colouring in the separate small container.

5. Using a dropper or a syringe squirt some coloured detergent into your oil and water filled jar.

7. If you would like to see a different reaction try pouring a teaspoon of salt into the mixture and watch what happens.

Oil and water experiment explanation: What is happening?

There are a lot of interesting things to note during this experiment.

Firstly oil and water do not mix. Even if you shake the jar the oil will immediately separate from the water as soon as it settles. Oil molecules are attracted to other oil molecules so they stick together. The same goes for water molecules….. so they just don’t mix – they are immiscible .

Secondly, the oil always floats on top of the water because the oil has a lower  density than water. You can find out why liquids layer by density in our Density Experiment .

Detergent is different again. It is attracted to both water and oil molecules. Detergent grabs onto both types of molecules causing oil droplets to be suspended in the water. When you shake the jar the detergent molecules adhere the water and oil together forming an emulsion. An emulsion is the combination of molecules that are not normally attracted to each other, that don’t usually mix. That is why detergent is so useful for cleaning greasy dishes!

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Ali Wright is mum to two young mini makers – their favourite place to be is around the craft table with glitter in their hair. Ali's focus is on process oriented art as she loves watching her kids experiment with creative materials. When not busy with art and craft, you'll likely find them at work and play in their small city garden. As the mini makers love a good mess, their days include lots of water and messy play!

i just have a simple question. Do you have to use a glass jar? Can it be plastic?

Hi Cheryl, plastic will work too 🙂 Cheers Ali

hello, is there any safety risks involved or no ?

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Hi! What type of Chemical Reaction is this? Your answer is very much appreciated.

can you use dishwashing liquid instead of detergant?

So, why does detergent separate water and oil?

Comments are closed.

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Mixing Oil & Water Science Experiment

Have you ever heard the saying, “Oil and water don’t mix”? For this easy science experiment, we observe exactly what does happens when we mix oil and water, then we’ll add another item to the mix to see how it changes!

With only a few common kitchen items, kids can explore density and the reaction of adding an emulsifier (dish soap) to the experiment. A printable instruction sheet with a materials list, demonstration video, and a simple scientific explanation are included.

JUMP TO SECTION: Instructions | Video Tutorial | How it Works

Supplies Needed

• Glass Jar with a lid (a pint canning jar works great)
• 1 cup Water
• Food Coloring
• 1 cup Oil (we used vegetable oil)
• 2 teaspoons Dish Soap

Mixing Oil & Water Science Lab Kit – Only $5

Use our easy Mixing Oil & Water Science Lab Kit to grab your students’ attention without the stress of planning!

It’s everything you need to  make science easy for teachers and fun for students  — using inexpensive materials you probably already have in your storage closet!

Mixing Oil & Water Science Experiment Instructions

Step 1 – Start by filling the jar with 1 cup of water.

Step 2 – Add a few drops of food coloring to the water and stir until combined. Make some observations about the water. What happened when the food coloring was added? Was it easy to mix the food coloring into the water? Does the food coloring stay mixed with the water? What do you think will happen when we pour the oil into the jar? Write down your hypothesis (prediction) and then follow the steps below.

Step 3 – Next pour 1 cup of oil into the jar. Make a few observations. Does the oil behave the same was as the food coloring did when you added it to the water?

Step 4 – Securely tighten the lid on the jar and shake it for 15-20 seconds.

Step 5 – Set the jar down and watch the jar for a couple of minutes. Observe what happens to the oil and the water and write down your findings. Did the oil and water stay mixed together? Was your hypothesis correct? Do you think there is anything else that can be added to the jar to prevent the oil and water from separating?

Step 6 – Next, take the lid off the jar and squirt in 1-2 teaspoons of dish soap.

Step 7 – Tighten the lid back on the jar and shake again for another 15-20 seconds.

Step 8 – Set the jar down and watch the liquid for a minute or two. Observe what happens to the oil and the water now that the dish soap has been added to the mix. Write down your findings. Did the oil and water stay mixed together this time? Do you know why adding the dish soap preventing the oil and water from separating? Find out the answer in the how does this experiment work section below.

Video Tutorial

How Does the Science Experiment Work

The first thing you will observe is that oil and water will not stay mixed together, no matter how hard you shake the jar. Instead, the oil slowly rises to the top of the water. This is because of the density of the two liquids. Density is a measure of the mass per unit volume of a substance. Water has a density of 1 g/mL (g/cm3). Objects will float in water if their density is less than 1 g/mL. Objects will sink in water if their density is greater than 1 g/mL. The oil is LESS dense than the water. This is because the molecules of oil are larger than the molecules of water, so oil particles take up more space per unit area. As a result, the oil will rise to the top of the water.

The second thing you will observe is that adding dish soap to the mixture changed the results of the experiment. When oil, water and dish soap are mixed together, the oil and water don’t separate like they did when they were the only two items in the jar. This is because of the chemistry of the oil, water and soap molecules.

Oil (and other fats) are made of nonpolar molecules, meaning they cannot dissolve in water. Water is made of polar molecules that can dissolve other polar molecules. Soap is made of molecules that have a hydrophilic (“water-loving”) end and a hydrophobic (“water-fearing”) end. Without soap, water and oil cannot interact because they are unlike molecules. When you add soap to the mixture, the hydrophobic end of the soap molecule breaks up the nonpolar oil molecules, and the hydrophilic end of the soap molecule links up with the polar water molecules. Now that the soap is connecting the fat and water, the non-polar fat molecules can be carried by the polar water molecules. Now the oil and water can be mixed together and stay mixed together!

I hope you enjoyed the experiment. Here are some printable instructions:

Mixing Oil & Water Science Experiment

• Glass Jar with a lid (a pint canning jar works great)

Instructions

• Start by filling the jar with 1 cup of water.
• Add a few drops of food coloring to the water and stir until combined.
• Pour 1 cup of Oil into the jar.
• Securely tighten the lid on the jar and shake it for 15-20 seconds.
• Set the jar down and watch the liquid for a minute or two. Observe what happens to the Oil and the Water.
• Next, take the lid off the jar and squirt in 1-2 teaspoons of dish soap.
• Tighten the lid back on the jar and shake again for another 15-20 seconds.
• Set the jar down and watch the liquid for a minute or two. Observe what happens to the Oil and the Water now that the dish soap has been added to the mix.

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October 4, 2017 at 11:43 am

Super ….. !

October 6, 2017 at 12:12 pm

Hi ! This gives us really good experiment

November 6, 2017 at 3:40 pm

This was the best science fair project ever

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December 10, 2017 at 10:38 am

This experiment is fun

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Adding Soap to Oil & Water

Why Oil Won't Mix in Water?

If two of your friends mix like oil and water, and you invite them both to a party, things could get awkward. Oil and water are immiscible , which means they don't mix. If your friends have to stay in the same room, they'll probably end up on opposite sides, glaring at each other. This is essentially what happens when you add oil to a container of water: The oil and water molecules stay apart, and because oil is less dense, the oil molecules gravitate to the top of the container and leave the lower part of the container to the water molecules.

Add soap to a mixture of oil and water, however, and things are different. Soap acts like a third person who is on good terms with both of your friends and can make them feel comfortable enough to stay in the same room. Soap doesn't make oil dissolve in water, but it helps break the oil molecules into smaller ones that can disperse in water.

How Soap Mediates Between Oil and Water

When two hydrogen atoms combine with an oxygen atom to form a water molecule, the hydrogens migrate to one side of the oxygen, creating a charge difference between the two sides. Water molecules electrostatically attract each other to form a hydrogen bond, which isn't as strong as the covalent bond holding the molecules together but is still quite strong. Water will mix only with other polar molecules or charged ions with an electrical attraction sufficient to break, or at least modify, this hydrogen bond.

Oil molecules are much larger than water molecules, and more important, they don't have a polar charge . When you pour oil into water, the oil molecules can't coax the water molecules away from their hydrogen bond, so the oil molecules clump together and form large globs that migrate to the surface, where they form a separate layer.

The soap molecule structure is a long string of hydrocarbons with one uncharged end and the other end ionic, or charged. The soap molecule is hydrophilic and hydrophobic , meaning that it is both attracted to and repelled by water. Because the uncharged end mixes with oil, and the charged end mixes with water, soap molecules can break the oil molecules into smaller ones and allow the water molecules attached to them to surround the smaller oil fragments, creating an emulsion.

Oil, Water and Soap Experiment

You can see this dynamic in action by pouring vegetable oil into a glass of water. Note how the oil forms beads that migrate to the surface. You can break these beads apart by shaking the glass, but as soon as the shaking stops, the beads reform and the oil rises again.

Now add a few squirts of dish soap and shake again. This time, the mixture will become cloudy. The cloudiness occurs because the soap breaks the oil molecules into smaller fragments and disperses them throughout the solution. The oil didn't dissolve in the same way that salt dissolves in water; the molecules are just too small and scattered too far apart to form into clumps, but they will regroup if you let the container stand overnight.

Soap Cleans Greasy Dishes

A useful oil and water experiment conclusion is that trying to clean greasy and oily dishes with water alone is bound to fail, because the oil won't mix and will stay on the dishes, no matter how much water you use. Hot water helps, but only a little. You need soap to do the job right, because soap breaks the oil molecules apart and allows the water molecules to surround them, so they will wash away.

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• Chemistry Libre Texts: Fats and Oils
• Scientific American: Mix It Up with Oil and Water
• Oregon Museum of Science and Industry: Oil and Soap

About the Author

Chris Deziel holds a Bachelor's degree in physics and a Master's degree in Humanities, He has taught science, math and English at the university level, both in his native Canada and in Japan. He began writing online in 2010, offering information in scientific, cultural and practical topics. His writing covers science, math and home improvement and design, as well as religion and the oriental healing arts.

Photo Credits

Abstract image of oil drops in water image by George Dolgikh from Fotolia.com

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May 24, 2018

Mix It Up with Oil and Water

A science shake-up activity from Science Buddies

By Science Buddies & Megan Arnett

A little mixup: Use kitchen chemistry to make oil and water blend. 

George Retseck

Key concepts Chemistry Surfactants Density Polarity

Introduction You may have heard people say, “Those two mix like oil and water,” when they’re describing two people who don’t get along. Maybe you’ve also noticed shiny oil floating on the surface of water puddles after it rains. In both cases you understand that water and oil don’t go well together—but have you ever wondered why? So many other things can dissolve in water—why not oil? In this activity we’ll explore what makes oil so special, and we’ll try making the impossible happen: mixing oil and water!

Background Unlike many other substances such as fruit juice, food dyes or even sugar and salt, oils do not mix with water. The reason is related to the properties of oil and water. Water molecules are made up of one oxygen atom and two hydrogen atoms. In addition to having this very simple structure, water molecules are polar, which means there is an uneven distribution of charge across the water molecule. Water has a partial negative charge from its oxygen atom and partial positive charges on its hydrogen atoms. This polarity allows water molecules to form strong hydrogen bonds with each other, between the negatively charged oxygen atom on one water molecule and the positively charged hydrogen atoms of another. Other molecules such as salts and sugars are able to dissolve in water because of its polarity as well. The charges at either end of the water molecule help break up the chemical structures of other molecules.

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Oils, by contrast, are nonpolar, and as a result they’re not attracted to the polarity of water molecules. In fact, oils are hydrophobic, or “water fearing.” Instead of being attracted to water molecules, oil molecules are repelled by them. As a result, when you add oil to a cup of water the two don’t mix with each other. Because oil is less dense than water, it will always float on top of water, creating a surface layer of oil. You might have seen this on streets after a heavy rain—some water puddles will have a coating of oil floating on them.

In this activity we will test the power of surfactants to help us mix oil and water. The surfactant we will use is dish detergent, which helps break up the surface tension between oil and water because it is amphiphilic: partly polar and partly nonpolar. As a result, detergents can bind to both water and oil molecules. We’ll see the results of this property in this activity!

2 clear plastic water bottles with lids

2 cups of water

One-half cup of oil (olive, cooking or vegetable oils will all work)

Liquid dishwashing soap

Clock or timer

Permanent marker

Measuring cup

Measuring spoon

Food coloring (optional)

Preparation

Remove any labels from your water bottles.

Use your marker to label the bottles: Label the first “Oil+Water” and the second “Oil+Water+Soap.” Write the labels as close to the tops of the bottles as possible.

Pour one cup of water into each bottle.  

Carefully measure and pour one-quarter cup of oil into the bottle labeled Oil+Water. Allow the bottle to sit on a countertop or flat surface while you observe the water and oil. Does the oil sink to the bottom of the bottle, sit on top of the water or mix with it?

Repeat this step, adding one-quarter cup oil to the bottle labeled Oil+Water+Soap. Does the oil sink to the bottom, sit on top of the water or mix with it?

Carefully add three tablespoons of dish soap to the bottle labeled Oil+Water+Soap. Try not to shake the bottle as you add the dish soap.

Make sure the bottle caps are screwed on tightly to each bottle.

Holding a bottle in each hand, vigorously shake the bottles for 20 seconds.

Set the bottles down on a flat surface with plenty of light.

Note the time on your clock or set a timer for 10 minutes.

Observe the contents of each bottle. Hold them up to a light one at time so you can clearly see what is happening inside the bottle. Did anything change when you shook the bottles? Do the mixtures look the same in the both? If not, what is different between them? How would you explain the differences that you observe?

After 10 minutes have passed look at the contents of the bottles and note the changes. What does the oil and water look like in each bottle? Has the oil mixed with the water, sink to the bottom or rise to the top?

Extra:  Add food coloring to the water to get a lava lamp effect

Extra:  Test other types of soap, such as toothpaste, hand soap and shampoo by mixing them with oil and water. 

Observations and results In this activity you combined oil and water then observed how adding dish detergent changed the properties of this mixture. First you should have noticed that when you added the oil to the water they did not mix together. Instead the oil created a layer on the surface of the water. This is because oil is less dense than water and therefore it floats to the surface. When you shook the Oil+Water bottle you might have noticed the oil broke up into tiny beads. These beads, however, did not mix with the water. After you let the Oil+Water bottle sit for 10 minutes you should have observed the oil and water starting separating again almost immediately, and after another 10 minutes there was once again two distinct layers in your bottle.

In contrast you should have found shaking the Oil+Water+Soap bottle resulted in a lot of foam, but instead of immediately starting to separate, the mixture was a cloudy, yellow color. Eventually the oil and water should have separated into two layers again, but these layers should have appeared less distinct and cloudier than the layers in your Oil+Water bottle.

The difference between the two bottles results from adding dish detergent to the Oil+Water+Soap bottle. The detergent molecules can form bonds with both water and oil molecules. Therefore, although the oil and water aren’t technically mixing with each other, the dish detergent molecules are acting as a bridge between oil and water molecules. As a result, the oil and water molecules aren’t clearly separated in the bottle. Instead, you see a cloudy mixture, resulting from the oil, soap and water chains you’ve created by adding dish detergent.

More to explore Goo-Be-Gone: Cleaning Up Oil Spills , from Science Buddies Make Your Own Lava Lamp , from Scientific American The Chemistry of Clean: Make Your Own Soap to Study Soap Synthesis , from Science Buddies Science Activities for All Ages! , from Science Buddies

This activity brought to you in partnership with Science Buddies

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Oil and Water Experiment

This classic oil and water experiment is sometimes referred to as “fireworks in a jar” because it looks like fireworks falling down from the oil. Kids will love learning about density and how oil and water do not mix in this fun and easy science experiment!

RELATED: Rain Cloud in a Jar

Oil and Water Science Experiment

This simple science experiment explores density using oil and water. Expand this further by mixing or trying other oils – does it act the same way? You can even use a pipette to add drops of colored water to oil in a jar or cup and observe what happens.

What is Density?

Density is the amount of mass per unit of volume. Let’s say you have two objects and they are the same size. If one object is heavier, then it is denser and if the other object is lighter, then it is less dense.

What you will see in this experiment is that oil is less dense than water, so it will float on top of the water.

The Science Behind It

Oil and water do not mix. Oil is less dense than water and floats on top of the water. Food coloring is water-based so it mixes with the water. When you add the food coloring to the oil it will not mix. Once you add the oil to the water, the food colored droplets start to drop down since they are heavier than the oil. Once they drop into the water they start to dissolve and look like tiny explosions (or fireworks).

Supplies Needed

Vegetable Oil – we used canola oil

Food Coloring

A Clear Jar or Vase

Watch the Video Tutorial Here

Steps to do an oil and water experiment.

1. Fill your jar or vase 3/4 full with water.

2. Add oil into a bowl. You do not need a lot like we used – you can even just use about 4 tablespoons of oil for a thin layer. A little more oil will show the difference in density slightly better for kids.

3. Add 4 -5 drops of food coloring for each color you want to add. We used green, blue and purple food coloring. You can use any colors you’d like but we would recommend no more than 3 as the colors will mix quickly and will make it harder to see them dropping down.

4. Whisk the food coloring into the oil. You can point out at this stage that you can already tell the oil and water will not mix.  It’s best to whisk and add the oil straight into the jar or vase before the food coloring settles on the bottom of the bowl or or it may not form droplets when you add it to the water.

5. Add the oil into the water.

Now wait and see all of the little drops start to come down from the oil (making “fireworks”).

We love how easy this simple science experiment is – and kids will love to observe or make their own fireworks in a jar too!

More Science Experiments for Kids

Try this fun and easy Grow a Rainbow Experiment . You only need washable markers and paper towel!

For another fun experiment, make some oobleck! 

Try a rainbow rain cloud in the jar experiment!

Related Ideas:

Cloud Dough

The BEST Playdough Recipe

How to Make Slime With Contact Solution

50+ Christmas Crafts for Kids

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Clean It Up – Oil Spill Experiment

February 20, 2020 By Emma Vanstone Leave a Comment

An oil spill is when sea water is contaminated with oil. This can be an accident or human error. Oil spills can be massively damaging to marine wildlife and also humans if the oil gets into the food chain . This hand-on oil spill science experiment is not only great for helping children visualise the effects of an oil spill, but also demonstrates how water and oil don’t mix and why oil floats on water .

Oil Spill Experiment for Kids

You’ll need

Clear plastic container

Vegetable oil

Spoon or pipette

Cotton wool

Cotton buds

Paper towel

Oil Spill Investigation Instructions

Step 1 – add oil to water.

Half fill the clear container with water. Drop a small amount of oil onto the water.

The oil will float on top of the water. Even if you shake the container ( cover it first ) the oil and water will separate again.

Use a cotton bud to move the oil around surface of the water.

Step 2 – Oil Clean Up

Pour enough water into the tray so the surface is completely covered and the tray is about half full.

Carefully drop two tablespoons of oil onto the surface of the water.

Experiment with the absorbent materials to discover which cleans up the oil spill the best.

Oil Spill Challenge s

Try to build something to contain oil to one area of the tray.

Try the experiment again, but this time use the same amount of each absorbing material and collect the oil for the same amount of time. Which material absorbs the oil the most effectively?

Another idea is to dip a feather in the oily water and watch as it starts to feel heavier. Imagine being a bird with oil covered feathers.  This activity can be further extended by exploring different methods of cleaning oil covered feathers. Water and water with washing up liquid are great things to try first.

Read about the biggest oil spills in history .

If you found our oil spill science experiment useful you might also enjoy our edible greenhouse gas models .

Last Updated on November 3, 2021 by Emma Vanstone

Safety Notice

Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

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Oil Spill Experiment

You’ve heard about oil spills on the news or maybe read about the cleanup in the newspaper, but did you know you could learn about ocean pollution right at home or in the classroom? This big idea is made tangible for kids with this easy oil spill experiment. This eye-opening oil spill activity will sure to be a hit with your kids, ocean science never goes out of style!

 OIL SPILL CLEANUP EXPERIMENT FOR KIDS

Ocean Pollution

Add this oil spill lab to your ocean lesson plans year. Learn more about ocean pollution as you create your own oil spill model and try to find ways to clean up the oil.

While you’re at it, make sure to check out these other fun ocean science activities !

Our science experiments are designed with you, the parent or teacher, in mind! Easy to set up, quick to do, most activities will take only 15 to 30 minutes to complete, and are fun! Plus, our supplies lists usually contain only free or cheap materials you can source from home!

This oil spill activity might get a bit messy but then again oil spills are a messy topic too! Use this oil spill demonstration with your kids to express the importance of caring for our natural resources. You can also check out these simple  ocean activities  for younger kids.

Watch the Video!

What is an oil spill.

An oil spill is a form of pollution generally found in a marine ecosystem. However, oil spills can also happen on land. They occur when oil leaks or spills into the water, such as rivers or lakes!

In the oil spill experiment, you will add the oil into a water tray representing the marine environment.

What causes an oil spill?

Accidents often cause oil spills, but they can also be caused by human error or carelessness. These accidents involve tankers, barges, oil drill rigs, and other places or methods of transportation that store or hold large amounts of oil.

Why are oil spills harmful?

Oil spills are harmful to marine birds, mammals, fish, and shellfish. Oil coats the feathers and fur of marine life, leaving them susceptible to hypothermia (being too cold) because their fur or feathers cannot protect them from the weather.

Additionally, an oil spill can contaminate the food supply or food chain. Marine mammals that eat fish or other food exposed to an oil spill may be poisoned by oil.

How to Clean Up an Oil Spill

Below, you will try several ways to clean up the oil spill, including Dawn dish soap.

I’m sure we have all seen the commercials for Dawn dish soap and how it’s helped clean thousands of animals affected by oil spills, but how does it do that? Soap breaks up the oil into smaller drops that can mix with the water and rinse away.

The chemistry behind soap is the key! Each end of the soap is made of different molecules. One end hates water (hydrophobic), and the other loves water (hydrophilic).

The oil is then broken up into tinier droplets and is no longer one big clump, it’s easier to remove!

The chemicals that clean actual oil spills work similarly to dish soap but on a bigger lever. You can read more about various oil spill clean up methods  here.

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How to Set Up an Oil Spill Experiment

Gather the following supplies and get started. This could get a little messy!

• Vegetable Oil
• Dawn Dish Soap
• Medicine Dropper
• Paper Towels
• Cotton Balls

Other options to try include a very fine mesh strainer or cheesecloth!

Oil Spill Cleanup Activity Set Up:

STEP 1:  Fill the tin pan/ tray half full of water. 

STEP 2: Pour oil into the water.

STEP 3: Try different ways to clean up the oil.

• Can you use cotton balls?
• How about paper towels?
• Did you try the spoon or medicine dropper to scoop out the oil?

STEP 4: Lastly, try using the Dawn Dish Soap.

Extend the Activity – Adapt for Ages

Young children (ages 3-6):.

Simplified Explanation : Use language appropriate for their age to provide a simple explanation of oil spills and why they’re harmful to animals and the environment.

Hands-On Exploration : Allow them to explore the materials freely, focusing more on sensory exploration rather than structured cleanup.

Guided Assistance : Offer assistance and guidance as they experiment with different tools. Focus on developing basic motor skills and fostering curiosity.

Creative Expression : Encourage imaginative play and storytelling about cleaning up the “ocean” and saving the “animals”.

Short Attention Spans : Keep the activity short and engaging, as younger children may have shorter attention spans.

Elementary School Children (Ages 6-12):

Educational Discussion : Provide a more detailed explanation of oil spills and their environmental impact, using age-appropriate language. Discuss concepts like pollution and conservation.

Structured Cleanup : Introduce specific challenges or goals for cleanup, such as using only specific tools or cleaning up within a time limit.

Problem-Solving : Encourage critical thinking and problem-solving as they experiment with different cleanup methods. Ask questions to prompt thinking, like “Why do you think this tool is effective?” or “How can we prevent spreading the oil?”

Teamwork : Foster teamwork by pairing children up or having them work in small groups to clean up the oil spill together.

Reflection: After the activity, discuss what the students learned and how they can apply it to real-life situations. Use our questions for reflection!

TIP: For older kids, you can also have graduated cylinders available. Measure the oil into the cylinder before pouring it into the water. Then, have them use a spoon to collect the same amount of oil and put it back into the cylinder.

Set a timer and see how much oil is recollected at the end of the given time!

CHALLENGE: What other ways can the kids come up with to remove the oil from the pan?

Oil Spill Science Projects

Do you want to turn this oil spill experiment into a science fair project? Check out these helpful resources below.

• Science Project Tips From A Teacher
• Science Fair Board Ideas
• Easy Science Fair Projects

Turn this science experiment into a fantastic presentation about the best oil spill clean up method along with your hypothesis. Learn more about the scientific method for kids and variables in science .

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Learn More About Our Oceans

• Beach Erosion Activity
• Stormwater Runoff Project
• How Do Whales Stay Warm?
• Ocean Acidification: Seashells In Vinegar Experiment
• Fun Facts About Narwhals
• Ocean Currents Activity
• Layers of the Ocean

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Seven-Layer Density Column

Anyone can stack blocks, boxes, or books, but only those with a steady hand and a little understanding of chemistry can stack liquids.

Print this Experiment

What if you could stack seven different liquids in seven different layers?

Experiment Videos

Here's What You'll Need

Light corn syrup, vegetable oil, dawn dish soap (blue), rubbing alcohol, lamp oil (select a cool color like red, available at a department store), glass cylinder, food coloring, food baster, seven plastic cups, scale (optional), let's try it.

Measure 8 ounces of each type of liquid into the seven plastic cups. Depending on the size of the glass cylinder, you might need more or less of each liquid—8 ounces is just a good starting point. You may want to color the corn syrup and the rubbing alcohol with a few drops of food coloring to create a more dramatic effect in your column. Here is the order of layers starting from the bottom and working your way to the top:

Honey Corn Syrup Dish Soap Water Vegetable oil Rubbing alcohol Lamp oil

Start your column by pouring the honey into the cylinder. It is very important to pour the liquids carefully into the center of the cylinder. Make sure the honey does not touch the sides of the cylinder while you are pouring. It’s important to let each layer settle before adding the next one. Take your time and pour slowly and carefully.

The next layer is corn syrup. Again, try not to let the corn syrup touch the sides of the container as you’re pouring. The key is to pour slowly and evenly.

Repeat the same procedure with the dish soap. Pour the soap directly into the middle of the layer of corn syrup . . . and take your time pouring!

Stop for just a second to enjoy your success. You’re almost halfway to your goal of stacking seven layers of liquid. The next liquid is water, and you’ll need to use the food baster—it’s like a giant medicine dropper for food. From this point forward, it’s okay to let the liquids touch the sides of the cylinder. In fact, it’s a must! Dip the tip of the food baster in the cup of water, squeeze the bulb, and draw up some water. Rest the tip of the food baster on the inside wall of the cylinder and slowly squeeze the bulb. Let the water slowly trickle down the glass to create the next layer. Take your time!

You’ll use the food baster once again for the next layer—vegetable oil. Use the inside wall of the cylinder to let the vegetable oil slowly trickle down and form the next layer.

Wash the food baster with some soap and water in the sink before moving on to the rubbing alcohol. If you have not already colored the rubbing alcohol, use a couple drops of food coloring to make sure this layer isn’t confused with water. Use the food baster and the inside wall of the cylinder to add this next layer.

You’re one layer away from success. Again, rinse the food baster in the sink before moving on to the lamp oil. Since lamp oil is flammable, you must do this last step away from any open flames. Use the food baster to draw up some lamp oil, which has a low surface tension and easily leaks out of the food baster. Keep your finger over the tip as you transport it over to the cylinder. By now you’re a pro at this. Use the baster and the inside wall of the cylinder to slowly add the final liquid layer.

Take your much-deserved bow and accolades from the guests in the viewing stands (or your friends hanging out in the kitchen). You’ve made a seven-layer science burrito, so to speak.

How Does It Work

The science secret here is density . Density is a measure of how much mass is contained in a given unit volume (density = mass divided by volume). If mass is a measure of how much “stuff” there is in an object or liquid, density is a measure of how tightly that “stuff” is packed together. Based on this density equation (Density = Mass ÷ Volume), if the weight (or mass) of something increases but the volume stays the same, the density has to go up. Likewise, if the mass decreases but the volume stays the same, the density has to go down. Lighter liquids (like water or rubbing alcohol) are less dense or have less “stuff” packed into them than heavier liquids (like honey or corn syrup). Every liquid has a density number associated with it. Water, for example, has a density of 1.0 g/cm 3 (grams per cubic centimeter—another way to say this is g/mL, which is grams per milliliter). Here are the densities of the liquids used in the column, as well as other common liquids:

The numbers in the table are based on data from manufacturers of each item. Densities may vary from brand to brand. You’ll notice that according to the number, rubbing alcohol should float on top of the lamp oil, but we know from our experiment that the lamp oil is the top layer. Chemically speaking, lamp oil is nothing more than refined kerosene with coloring and fragrance added. Does every brand of lamp oil exhibit the same characteristics? Sounds like the foundation of a great science fair project. So, the next time you’re enjoying a glass of iced tea, you’ll know why those ice cubes float. That’s right . . . it’s all about density.

Take It Further

If you want to create an even cooler science burrito, add the “meat and black olives.” In other words, select a few items from around the house (safety pin, key, staple, peanut, raisin, chocolate chip, small rubber bouncy ball, ping pong ball, etc.—be creative!) and carefully drop each item individually into the center of the cylinder. Some items will stay on or near the top of the stack of liquids and other items will sink part or all of the way down to the bottom of the cylinder. Why the difference? The densities and masses of the objects you drop into the liquids vary. If the layer of liquid is more dense than the object itself, the object stays on top of that liquid. If the layer of liquid is less dense than the object, the object sinks through that layer until it meets a liquid layer that is dense enough to hold it up. Here’s something else you can do to illustrate the connection between weight (or mass) and density. Set up a scale and weigh each of the liquids from your column. Make sure that you weigh equal portions of each liquid. You should find that the weights of the liquids correspond to their level in the column. For example, the honey will weigh more than the corn syrup. By weighing these liquids, you will find that density and weight are closely related.

Safety Information

Lamp oil is a flammable liquid and must be handled with care. Adult supervision is required. Need I remind you to never light your Seven-Layer Density Column on fire? Just don’t do it.

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Pepper and Soap Experiment

The pepper and soap experiment is one of the easiest science activities to help children understand buoyancy and surface tension. The theoretical part of science lessons can sometimes be very abstract and confusing to understand. But, performing simple Science experiments for kids like the Pepper and Soap Experiment helps children learn those difficult concepts easily.

Performing The Pepper Dish Soap Experiment

The pepper and soap experiment is one of the easiest science activities for kids and needs very few ingredients. 

Here is a step-by-step guide to performing the Pepper and Soap Experiment with your kids:

Things You’ll Need For The Pepper And Soap Experiment

Step-by-step guide to performing the pepper and soap experiment, the science behind with pepper and dish soap experiment, why should you perform the pepper and soap science experiment.

The Pepper and Soap Experiment is really simple, all you need are dish soap, water, and some black pepper. These are simple ingredients that you can easily find in your kitchen or pantry.

• Liquid dish soap
• Black Pepper
• A small bowl

Download Pepper & Soap Printable

Here is a step-by-step guide to set up and perform the pepper soap experiment with your child:

Fill the plate with water almost to the edge, but ensure that it doesn’t overflow.

Sprinkle some black pepper over the water. You’ll notice that the pepper floats on the water. This happens because of buoyancy.

Dip your finger in the center of the plate. Did you notice any change? Not much happened, right? You may have just got some pepper flakes stuck to your finger. Imagine that these pepper flakes are germs. If you accidentally touch your face or mouth with hands that are contaminated with germs, it could make you sick.

Now, add a drop or two of liquid soap into a small bowl. Ask your child to stick their finger into the bowl and get some soap on their finger.

Now, dip your soap-covered finger in the bowl with the water and pepper flakes. See anything different this time? You’ll notice that the pepper flakes (germs) move away to the edge of the plate. Your soapy finger pushed the pepper flakes away to the edge of the plate. 

This simple science experiment with pepper and dish soap is fun to watch for kids and adults. It is fun to see how the soap pushes away all the pepper flakes to the edge of the plate. Help your child understand the science behind this science experiment with pepper and dish soap.

Why do the pepper flakes float on the water?

The pepper flakes float because of buoyancy, which is the upward force exerted by a liquid. This force causes an object placed on the liquid to float.  

So, why did the pepper flakes move away to the edge of the plate?

This happens because the liquid dish soap changes the surface tension of water. 

The surface tension of a liquid is the tendency of liquid surfaces to resist an external force due to the cohesive nature of its molecules. The pepper flakes are so light, it floats on the water surface due to surface tension. The addition of soap broke the surface tension of water, but the water molecules want to keep the surface tension intact. So they pull away from the soap along with the pepper flakes. This pushes the pepper or “germs” away from your soap covered finger. This is why soap is such a great cleaning agent and so effective in cleaning dishes and taking all the grease and dirt away. 

This pepper and soap experiment also shows how germs are removed from hands with soap. The pepper flakes or “germs” were not chased away until you added soap to the bowl. 

This science experiment doesn’t just teach science concepts like surface, tension, buoyancy etc. The Pepper and Soap Experiment is also a great way to help children understand the importance of washing hands. Handwashing is a hygiene practice that all kids must learn. It keeps away germs and helps prevent several infectious diseases. 

Ever since the world was hit by Coronavirus disease, the importance of handwashing has increased tenfold. Contaminated hands can spread the Covid-19 disease easily. So, washing hands is the first line of defense against the Covid-19 disease and cannot be ignored. One needs to wash their hands for at least 20 seconds with soap, to keep the germs away. Kids are usually negligent about such stuff, teaching them to wash their hands frequently is important.

We hope you liked the Pepper and Soap Experiment. For more kids learning resources, check Osmo. 

Frequently Asked Questions on Pepper and Soap Experiment

What are the materials required for pepper and soap experiment.

The materials required for Pepper and Soap Experiment are a small bowl, black pepper, water, an empty plate, and liquid dish soap.

What is kids will learn from Pepper and Soap Experiment?

The kids will learn from Pepper and Soap Experiment on how the pepper flakes float on the water, and why did the pepper flakes move away from the centre of the plate to the edge.

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Oil Spill Clean-Up Experiment

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Detergents, soaps and surface tension

In association with Nuffield Foundation

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Various experiments to observe the effects of detergents and soaps on the surface tension of purified and hard water

A fine insoluble powder, such as talcum powder, is sprinkled on a clean water surface in a beaker, a drop of detergent or soap solution added to the centre, and the effect observed as the surface tension of the water is changed. This can be repeated with other powders after cleaning the beaker and using fresh water samples. A needle can be carefully floated on a clean water surface and the effect of adding detergent or soap observed. Finally the same experiments can be repeated using samples of hard water to compare the effects.

This is a series of quick, simple, class experiments which can be extended or shortened as desired. Each experiment should take no more than two minutes, though the cleaning of the beaker between experiments may take up more time than expected. If a full range of experiments is desired, the time taken could amount to 30 minutes, but this may not be justified in terms of the learning objectives concerned.

• Beaker (250 cm 3 )
• Glass stirring rod
• Clean sewing needle (note 1)

Apparatus notes

• The sewing needle should be a fine needle, and for safety issued to students with the pointed end inserted into a piece of card bearing a safety warning about handling the needle.
• Talcum powder, in pepper pot or similar dispenser
• Other powders (see technical notes)
• Liquid detergent in a dropping bottle
• Liquid soap in a dropping bottle
• Access to a supply of purified water (distilled or deionised), about 1 dm 3  per working group
• Access to a supply of hard water

Health, safety and technical notes

• Read our standard health and safety guidance
• Other powders – Any powders used other than talcum powder, such as lycopodium powder or carbon powder, should be subject to a risk assessment. Lycopodium powder is a potential allergen.
• Liquid detergent – Any washing-up liquid or multipurpose detergent will suffice.
• Liquid soap - Genuine liquid soap or soap flakes from which the liquid can be made, is increasingly difficult to obtain. Wanklyn’s and Clarke’s soap solutions should still be available from chemical suppliers. Lux soap flakes are ideal for making liquid soap if you can source them. Granny’s Original and other non-branded soap flakes work fine but need to be used in solution as soon as they are made. They do not form a stable emulsion and precipitate out overnight. Note that most liquid hand washes are based on the same detergents as washing-up liquids and do not contain soap. To obtain soap solution from soap flakes – dissolve soap flakes (or shavings from a bar of soap) in ethanol – use IDA (Industrial Denatured Alcohol) (HIGHTLY FLAMMABLE, HARMFUL) – see CLEAPSS Hazcard HC040a and CLEAPSS Recipe Book RB000. Do not dilute with water.
• Hard water – A supply of hard water can be made by stirring solid calcium sulfate into a large volume of tap water, allowing to stand for some time then, after the undissolved solid has settled out, decanting the clear solution into a container suitable for students to collect their samples as required. Label as ‘Hard Water’. Allow about 1 dm 3  for each working group in the class.
• Half fill the beaker with purified water.
• Sprinkle the water surface carefully with a fine layer of powder.
• Add one drop only of detergent in the middle of the water surface. Observe what happens. Does the talcum powder stay on the surface, or does it sink?
• Clean the beaker thoroughly, half-fill again with purified water, and repeat steps two and three using a drop of liquid soap instead of detergent. Compare what happens to what happened in the previous experiment.
• Repeat steps three   and four, only this time use hard water instead of purified water. Are the results different from those obtained with purified water? If so, in what ways?
• Other powders may be available to test instead of talcum powder, to see whether the type of powder makes any difference. If you do test any of these, what differences do you find?
• Again using a clean beaker with purified water, try to float a fine sewing needle on the surface by carefully lowering it into the beaker, avoiding breaking the surface with your fingers, and dropping it from as close above the surface as possible. Once you have a needle floating, add a small drop of detergent to the water, but away from the needle. What happens?

Teaching notes

This series of brief experiments on the surface tension of water, and the effects of detergents and soaps on this, can serve as an introduction to the phenomenon of surface tension, with a discussion of results leading into simple theory. Alternatively, it could be used to illustrate prior teaching of the topic, leading to discussion of what is happening when detergents and soaps are added, including the differences found with hard water.

A diagram of the forces between water molecules at the surface and centre of a liquid.

There is a net force of attraction between the molecules of water (or any other liquid) holding the molecules together. For a molecule in the middle of the liquid, these forces, acting equally in all directions, more or less balancing out. For a molecule in the surface layer of the liquid, the forces do not balance out, and all the molecules in the surface layer are pulled towards each other and towards the bulk of the liquid. This brings these molecules closer to their neighbours until increasing forces of repulsion create a new balance, and gives rise to the phenomenon of surface tension.

When an object falls onto the surface, it has to push the water molecules apart. If the effect of the weight of the object is insufficient to match the attractive forces between molecules in the surface layer, the object will not enter the surface. Careful observation of the floating needle will show that the water surface is bent down under the weight of the needle, the surface tension causing it to behave as if the needle was supported by a flexible skin.

A diagram of the forces enabling a needle to float on water

Molecules of most detergents and soaps are long chain hydrocarbon molecules with an ionic group at one end, usually carrying a negative charge, thus making it an anion. This charge is balanced by the opposite charge of a soluble cation, for example Na + . The long hydrocarbon chains do not interact well with water molecules, and many of them are effectively ‘squeezed out’ to the interfaces between the water and the air or the glass sides of the beaker. The effect of these molecules on the water surface is to considerably weaken the forces between water molecules there, thus lowering the surface tension.

A diagram of a detergent or soap molecule, which is responsible for breaking down surface tension

When the drop of detergent is added to the powdered surface, the initial effect is to draw the powder back to the edges very rapidly as the detergent molecules form their own surface layer with a lower surface tension than the water. As the detergent gradually mixes with the water, the powder begins to sink, and a needle will now pass through the surface with ease under its own weight. However, if lycopodium powder is used, which is less dense than water, it remains at the edges. Other powders may clump into nodules if they are not wetted by the detergent solution.

A diagram showing detergent molecules in a beaker of water, some lining the surfaces and other forming clumps

In hard water there is a significant concentration of calcium, Ca 2+ , and/or magnesium, Mg 2+ , cations. These cations form an insoluble compound with soap anions, so instead of forming a surface layer, they are precipitated out, leaving the surface tension largely unchanged.

2COO − (aq) + Ca 2+ (aq) → (COO) 2 Ca(s)

However, the calcium and magnesium salts of many detergent molecules are soluble, so detergents lower the surface tension of hard water.

Additional information

This is a resource from the  Practical Chemistry project , developed by the Nuffield Foundation and the Royal Society of Chemistry. This collection of over 200 practical activities demonstrates a wide range of chemical concepts and processes. Each activity contains comprehensive information for teachers and technicians, including full technical notes and step-by-step procedures. Practical Chemistry activities accompany  Practical Physics  and  Practical Biology . 

© Nuffield Foundation and the Royal Society of Chemistry

• 14-16 years
• Practical experiments
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• Properties of matter
• Applications of chemistry

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Science project, pepper and soap experiment.

Rub-a-dub-dub, there’s pepper in my tub! In this experiment, you’ll use pepper floating on water to demonstrate how soap affects the surface of water. This is a quick experiment, but it’s so fun to watch that you’ll want to repeat it several times.

How does soap interact with water?

• Shallow bowl or pie tin
• Fill the bowl or pie tin with about an inch of water.
• Sprinkle pepper evenly across the surface. Try not to sneeze! The pepper flakes should float, not sink, upon the surface of the water.
• Squeeze a tiny bubble of dish soap onto a clean counter.
• Touch the tip of the toothpick to the bubble of dish soap. You'll want just a tiny amount of soap on the end of the toothpick.
• Set the toothpick carefully aside and pick up your notebook and pencil.
• What do you think will happen when you touch your soapy toothpick to the water? How will the pepper flakes react?
• Write down your best, often called a hypothesis , in your notebook.
• Now poke the soapy toothpick into the water, right in the center of the tin.
• What happens? Was your hypothesis correct?

Most of the pepper flakes should have darted to the sides of the pan, and some of the flakes should have fallen to the bottom of the pan. It may have looked like the soap was chasing the pepper flakes away.

The first question to ask is why the pepper flakes float. Why don’t they sink or dissolve in the water? Well, pepper is hydrophobic , meaning that water is not attracted to it. Because of that, the pepper can't dissolve in the water. But why do the flakes float on top of the water? Water molecules like to stick together. They line up in a certain way that gives the top of the water surface tension. Because pepper flakes are so light, and hydrophobic, the surface tension keeps them floating on top.

The next question to think about is why the pepper shoots to the sides when soap touches the water. Soap is able to break down the surface tension of water—that’s part of what makes soap a good cleaner. As the soap moves into the water, and the surface tension changes, the pepper no longer floats on top. But the water molecules still want to keep the surface tension going, so they pull back away from the soap, and carry the pepper along with them.

Do you think soap is the only substance that can break down water's surface tension? Try conducting the same experiment but with olive oil or hair spray. Do you think the pepper flakes will react in the same way?

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Bookmark this to easily find it later. Then send your curated collection to your children, or put together your own custom lesson plan.

Make Your Own Soap! Part 1: The Chemistry Behind Soap Making

In the middle of teaching some high school students about the chemistry of soap-making, I realised that I really, really wanted to try making some soap myself and write about it here.

My write-up ended up being really long, so I’ve made it a two-parter – Installment 1 is all about the chemistry, and Installment 2 is about the actual procedure (which you can also do at home with equipment and chemicals from the supermarket!).

You don’t need to understand the chemistry behind soap making to make soap, but knowing the background does mean that you can play around with your recipes and solve any problems you run into with minimal trial-and-error and wastage!

It’s also very interesting from a scientific point of view.

Jump to section:

What Is Soap?

Making soap – the saponification reaction, fats and oils, strong base, proportions.

Before we can start with the nitty gritty of chemical reactions – what even is soap?

If you’ve been following me for a while, you’ll remember me mentioning chemicals called surfactants , such as in my guest post on chemophobia on The Toast , and in this face washing guide .

Surfactants are nifty molecules that dissolve in both water- and oil-based substances, meaning they can clean oil off surfaces, and keep mixtures of oil and water-based liquids happy together (think mayonnaise – without egg yolk acting as a surfactant keeping everything mixed, it’d just separate into vinagrette dressing).

Surfactants have a charged water-loving, hydrophilic “head”, and a neutral, oil-loving, lipophilic “tail”.

Here’s what it looks like when it’s dissolving oil in water (e.g. in your dirty bathwater, or keeping the fat dissolved in your milk) – the surfactants hang out in the interface between the oil and water, holding everything together.

Soaps look something like this:

This particular soap molecule’s called sodium laurate. When it dissolves in water, the sodium (Na+ on the left) and the laurate (the rest of the diagram) split up. Here’s the laurate ion:

Looks familiar?

Yep, soaps are negatively charged surfactants!

They’re part of a class of chemicals called anionic surfactants (anionic = negatively charged), which includes the strongest cleaning agents. (Technically soaps are referred to as “salts of fatty acids” – I won’t use this terminology much but it’s here in case you ever need it.)

So, how do we get these useful things in our grubby little hands?

Soap is made from reacting a fat or oil (or a mixture) with a strong base (something with very high pH). The chemical structures of fats and oils generally look like this:

The left hand side (purple) is always the same – it’s based on a glycerin (aka glycerol) molecule. Each “O” represents an oxygen atom – there are 3 on glycerol, and these are chemically attached to 3 fatty acids (in blue, which will end up being the soap).

These can all be the same or different (in this drawing, I’ve drawn them all the same). Because there are three things and they’re joined to a glycerin molecule, fats and oils are called triglycerides .

The soapmaking reaction is called saponification , and after reacting, the mixture is said to be saponified . Saponification involves reacting the fat or oil with a strong base, usually sodium hydroxide (aka lye aka caustic soda), although you can also use potassium hydroxide (aka caustic potash).

This reaction breaks the triglyceride into the purple and blue parts, in other words, the glycerin and soap molecules.

Let’s have a closer look at each component of the reaction:

This is the most complicated and interesting part of the recipe. Different fats and oils can be used to make soaps with different properties. In fats and oils, the fatty acids (that’s the blue part, remember) differ.

There are two main types of fatty acids: saturated and unsaturated. (This is the same as the saturated and unsaturated fats that you hear about from dieticians!)

Saturated fatty acids have a straightforward zig-zag in their structure. The common ones we use in soap-making are lauric acid, myristic acid, palmitic acid and stearic acid, shown below.

This means that when they stack together neatly at a molecular level both before and after saponification, forming harder soaps (and harder blockages in your arteries, if you’re eating them).

Soaps made from saturated fatty acids are also more effective at cleaning – however, this means that they strip more natural oil away from your skin as well.

Unsaturated fatty acids have kinks in their structure, due to there being double bonds (the bits where the zig zag becomes two parallel lines).

Common unsaturated fatty acids used in soap-making are oleic acid, linoleic acid, alpha- and gamma-linolenic acid (these are also known as omega fatty acids – again, something you may have come across before in the context of nutrition), and ricinoleic acid. Because of their kinky shape, they don’t stack neatly at a molecular level and can slide around with lots of gaps, which means you end up with softer soap bars (and they don’t clog arteries if you eat them).

Soaps made from unsaturated fatty acids are less efficient at cleaning and are therefore gentler on the skin.

As well as the hardness of your soap and its cleansing powers, the amount of each saponified fatty acid in the final soap will also affect how the lather behaves . Generally, saturated fatty acids will give you a creamy, stable lather, while unsaturated fatty acids will result in a fluffy but unstable lather.

One notable exception though is ricinoleic acid (found in castor oil), which is unsaturated but gives a rich, fluffy lather that’s quite stable too. Unsaturated fatty acids also tend to go rancid more easily, as the double bond can react.

(Side note: animal and plant fats and oils are triglycerides – mineral oil and other oils derived from petroleum, on the other hand, aren’t triglycerides, so it’s impossible to make soap from them.)

You can also easily look up the fatty acid profiles of common fats and oils – they’ll differ for each batch of oil, so they’re really ballpark figures. Here are the three oils I’ll be using in the project (info from this amazing soap calculator ):

The bases used for soapmaking have to contain hydroxide – that’s the bit that acts to break up the fat or oil into glycerin and soap. Sodium hydroxide and potassium hydroxide are the 2 most commonly used bases for saponification.

Sodium hydroxide (also known as lye or caustic soda) is most commonly used, and results in a hard bar. Potassium hydroxide results in a soft bar, and is usually used for making liquid soap.

The reason for the difference is that the sodium ion is a bit smaller than the potassium ion – it interferes less with the stacking of the soap molecules at a molecular level, and just like with saturated vs. unsaturated fatty acids above, the more efficient the stacking, the harder the resulting soap.

Safety note: Strong bases are rather nasty things to play with – just like strong acids, they’ll burn your skin right off. Remember the scene from Fight Club? It’s not just artistic license – you will end up with a permanent scar!

I’ll go more into the safety considerations for soap making in the next post.

In the reaction diagram above, you’ll notice that you need 3 base particles to react with one fat or oil particle. Molecules are ridiculously tiny, so we can’t sit and count out the exact number we need to mix in our saucepan.

Those of you who have studied chemistry will know that there’s a method for calculating the ratios of components, but fats and oils tend to contain mixtures of fatty acids rather than a single sort of molecule, so it’s not a straightforward task!

Luckily, there are lots of soap calculators and saponification tables online with preprogrammed numbers that can do the dirty work for us – here are a few .

(If you use a particularly advanced soap calculator, it will also calculate the predicted properties of the soap made from whatever mixture of fats and oils you’ve chosen, just from the %s of each fatty acid, which is really nifty.)

These calculators let us work out what the perfect proportions would be, but remember that we’re not using super precise scientific instruments – we’re using kitchen scales, which will weigh quite a few molecules off (and by quite a few, I mean in the region of 2,500,000,000,000,000,000,000 – that’s the number of NaOH particles in a measly gram).

If we don’t have enough base, there’ll be too much fat/oil left over at the end – slapping grease on your skin doesn’t sound very cleansing! On the other hand, if we don’t have enough fat/oil, we’ll have strong base left over at the end in the soap bar – ouch!

The way we play it safe is by superfatting , which means adding a bit less hydroxide than we need – enough to be safe, but not so much that the soap ends up too greasy. This is also called a lye discount, and is usually around 5-8%.

This is the product that’s the same in all saponification reactions. Glycerin is a humectant moisturiser, which means it draws water to the skin to add moisture (it’s the stuff that makes this DIY nail polish remover so nourishing!). However, this also means it attracts water to your final bar of soap, making it turn to mush if you’re not careful.

Commercially mass produced soaps usually remove a lot of the glycerin to get around this issue, and some handmade soaps do too (using a process called “salting out”), but this is a bit more advanced than we need for this project.

• Soaps are surfactants , which means they dissolve in water and oils and can clean.
• Soapmaking involves reacting fats/oils with a strong hydroxide base , to form glycerin and soap (salts of fatty acids).
• Fat/oil molecules ( triglycerides ) are made up of glycerin chemically attached to 3 fatty acids.
• The specific fatty acids in the fats/oils you’re reacting will determine the properties of your final bar of soap.
• The strong hydroxide base you’ll be using to make a bar of soap will probably be sodium hydroxide, which has a high pH
• To calculate how much of each chemical you need in your reaction, you’ll need to use a soap calculator or saponification table .
• You’ll want to have a little excess fat/oil (5-8%) in your recipe, because being a tad greasy (moisturised) is better than burning your skin off! This is called superfatting .

That’s the chemistry behind soapmaking in a (rather large) nutshell. But how do we go from this to, well… actually having a bar of soap to use on your bod?

Part 2 will be all about the process – see you then!

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9 thoughts on “Make Your Own Soap! Part 1: The Chemistry Behind Soap Making”

This was great reading. I’m looking forward to the next installment! I’ve always been wary of working with acids and bases in the lab (I did cell and molecular biology, so it was minimal) but I think the pull of making my own soap might balance that out.

It’s not too bad if you’re prepared for it! With proper precautions it’s really quite safe 🙂

i always thought the chemistry behind soap was so interesting! out of my favorite topics in chem in school 🙂

It was one of my favourites too! I remember taking turns to stir the soap mixture in class 🙂

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Hello Great blog and explainations. I know this post is from 2014 but I was wondering if I can get some advice on how to make something like this https://www.benefitcosmetics.com/uk/en-gb/product/foamingly-clean-facial-wash You can click to see ingredients. It looks like a liquid soap with additional surfactant and an emuslifier

This is an excellent article.. I enjoyed every minute of reading and taking down notes. Thank you very much for the work.

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