filtration experiment definition

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What Is Filtration? Definition and Processes

Filtration is a process that separates solid particles from liquids or gases using a medium called a filter.

How Filtration Works

The requirements for filtration are:

• Feed – The “feed” is a suspension of particles in a fluid, which may be either a liquid or a gas.
• Filter – A filter is a lattice that won’t allow large particles to pass. The pore size and thickness of the filter determine the size of particles that are allowed. A surface filter traps particles on top, while a depth filter traps particles within the filter. Filter paper is an example of a surface filter, while sand is an example of a depth filter. The solid collected on a surface filter is called the “cake.” Trapped particles may clog a filter. This is called blinding. Sometimes filter aids are mixed with the fluid or placed on the filter to minimize blinding. Examples of filter aids include silica, cellulose, perlite, and diatomaceous earth.
• Filtrate – The filtrate is the fluid that passes through the filter. Filtration is often imperfect, so it’s common for a few particles to escape into the filtrate.
• Force – Filtration relies on some type of force to move the feed through the filter. This can be gravity drawing a fluid down, pressure pushing the mixture through the filter, or vacuum sucking the fluid through the filter.

Everyday Examples of Filtration

Filtration is important in the laboratory to separate and purify materials, but it’s also common in daily life. Here are some examples of filtration:

• Brewing coffee – During the brewing process, hot water passes over ground coffee. A coffee filter separates the grounds from the coffee, which is the filtrate. Steeping tea works much the same way, where the filter is a tea bag (a type of paper filter) or a tea ball (a metal filter).
• Face masks – Masks filter particles, minimizing the escape of pathogens from an infected person and the inhalation of outside particles. Pore size and thickness are significant factors in mask effectiveness.
• Kidneys – The kidneys are a biological filter. The glomerulus filters particles out of blood. Water and essential molecules are reabsorbed, while undesirable particles are broken down or encapsulated and removed.
• Air filters – Air conditioners often use HEPA filters to remove particles from air, while furnace use filters to prevent them from reaching heating elements.
• Water filters – Water filters filter out large particles, which may include pathogens. Usually these filters also use ion exchange to remove contaminants. An aquifer is a natural water filter that cleans water as it passes through sand and permeable rock.
• Oil filters – Oil filters prevent debris from harming engines.
• Belt filters – Belt filters recover precious metals in mining.
• Aquarium filters – Aquariums use fibrous filters to capture particulates.

Types of Filtration

There are several types of filtration. The best method for a task depends on whether the solid is suspended in the fluid or dissolved in it.

• General Filtration : General filtration is a basic type of filtration that uses gravity to draw the feed through the filter. Coffee makers rely on general filtration.
• Vacuum or Pressure Filtration : In one type of vacuum filtration, a Büchner flask and hose generate a vacuum to suck the feed through the filter. Usually, this vacuum filtration set-up gets help from gravity. Another type of vacuum filtration uses a pump to generate a pressure difference between the sides of the filter. Pump filters don’t need to be vertical.
• Cold Filtration : Cold filtration allows collection of dissolved particles. In this method, rapid cooling crystallizes the solid so it can be collected on the filter. In the laboratory, chilling the solution in an ice bath before filtration often does the trick.
• Hot Filtration : In contrast, hot filtration seeks to minimize crystal formation. Heating the feed, filter, and funnel help prevent the growth of crystals that could clog the filter or undesirable crystal formation in the filtrate. Stemless funnels find use in hot filtration because a long stem offers more surface area for crystal growth.

Difference Between a Filter and a Sieve

A sieve is a device that separates materials based on size using a screen or mesh. Sieves are also called sifts or strainers. Filtration and sieving work on the same principle, but a sieve only has a single layer of “holes.” Good examples of sieves are kitchen strainers and flour sifters. Some people consider a sieve to be a type of surface filter, while others consider them distinct separation methods.

Alternatives to Filtration

Filtration isn’t the only method used to separate mixtures. Two alternatives are decantation and centrifugation.

In decantation , a mixture separates based on differences in density and miscibility. The fluid is poured or siphoned off, leaving the solid. An advantage of decantation is that no material is lost on the filter medium. But, decantation doesn’t work for all mixtures.

Centrifugation uses centrifugal force to separate mixture components based on size, density, and viscosity. After centrifugation, solids form a firm cake. Decanting the liquid results in less loss of either liquid or solid after centrifugation.

• Ruhlman, Michael; Bourdain, Anthony (2007). The Elements of Cooking: Translating the Chef’s Craft for Every Kitchen . Simon and Schuster. ISBN 978-1-4391-7252-0.
• Sparks, Trevor; Chase, George (2015). Filters and Filtration Handbook (6th ed.). Butterworth-Heinemann. ISBN 9780080993966.

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Filter media

Filtering force.

• Filter types
• Special techniques

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filtration , the process in which solid particles in a liquid or gaseous fluid are removed by the use of a filter medium that permits the fluid to pass through but retains the solid particles. Either the clarified fluid or the solid particles removed from the fluid may be the desired product. In some processes used in the production of chemicals, both the fluid filtrate and the solid filter cake are recovered. Other media, such as electricity , light , and sound, also can be filtered.

The art of filtration was known to early humans, who obtained clear water from a muddy river by scooping a hole in the sand on a river bank to a depth below the river water level. Clear water filtered by the sand would trickle into the hole. The same process on a larger scale and with refinements is commonly used to purify water for cities.

The basic requirements for filtration are: (1) a filter medium; (2) a fluid with suspended solids; (3) a driving force such as a pressure difference to cause fluid to flow; and (4) a mechanical device (the filter) that holds the filter medium, contains the fluid, and permits the application of force. The filter may have special provisions for removal of the filter cake or other solid particles, for washing the cake, and possibly for drying the cake. The various methods used for treating and removing the cake, for removing the clarified filtrate, and for creating the driving force on the fluid have been combined in various ways to produce a great variety of filter equipment.

Filter media may be divided into two general classes: (1) thin barriers, exemplified by a filter cloth, filter screen, or common laboratory filter paper; (2) thick or en masse barriers, such as sand beds, coke beds, porous ceramics, porous metal, and the precoat of filter aid which is often used in the industrial filtration of fluids that contain gelatinous precipitates .

A thin filter medium offers a single barrier in which the openings are smaller than the particles to be removed from the fluid. A single thin filter medium usually is satisfactory if the layers of solid particles that accumulate on the medium produce a porous cake that is permeable to the fluid. If the filter cake is gelatinous or the particles are soft and compressible, rather than firm, the filter cake may “blind”; that is, the pores in the cake may close and stop filtration. If this happens, a filter aid or a thick filter medium such as the sand bed may be used.

Contrary to the situation with the thin medium, the pores in a thick filter medium such as a sand bed may be appreciably larger than the particles to be removed. The particles may travel for some distance along the tortuous path of the fluid through the medium but sooner or later will be entrapped in the finer interstices between the particles that constitute the filter bed. In this way the soft particles removed are distributed over a volume of filter medium that is sufficient to prevent blinding and stoppage of filtration. After solids accumulate the beds may be backwashed with clear fluid to clean the bed.

The fluid to be filtered will pass through the filter medium only if some driving force is applied. This force may be caused by gravity, centrifugation , application of pressure on the fluid above the filter, or application of vacuum below the filter or by a combination of such forces. Gravitational force alone may be used in large sand-bed filters and in simple laboratory filtrations. Centrifuges containing a bowl with a porous filter medium may be considered as filters in which gravitational force is replaced by centrifugal force many times greater than gravity. If a laboratory filtration is difficult a partial vacuum is usually applied to the container below the filter medium to increase the rate of filtration. Most industrial filtration processes involve the use of pressure or vacuum, depending upon the type of filter used, to increase the rate of filtration and also to decrease the size of the equipment required.

Filtration Definition and Processes (Chemistry)

Filtration: What It Is and How It's Done

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Filtration is a process used to separate solids from liquids or gases using a filter medium that allows the fluid to pass through but not the solid. The term "filtration" applies whether the filter is mechanical, biological, or physical. The fluid that passes through the filter is called the filtrate. The filter medium may be a surface filter, which is a solid that traps solid particles, or a depth filter, which is a bed of material that traps the solid.

Filtration is typically an imperfect process. Some fluid remains on the feed side of the filter or embedded in the filter media and some small solid particulates find their way through the filter. As a chemistry and engineering technique, there is always some lost product, whether it's the liquid or solid being collected.

Examples of Filtration

While filtration is an important separation technique in a laboratory, it's also common in everyday life.

• Brewing coffee involves passing hot water through the ground coffee and a filter. The liquid coffee is the filtrate. Steeping tea is much the same, whether you use a tea bag (paper filter) or tea ball (usually, a metal filter).
• The kidneys are an example of a biological filter. Blood is filtered by the glomerulus. Essential molecules are reabsorbed back into the blood.
• Air conditioners and many vacuum cleaners use HEPA filters to remove dust and pollen from the air.
• Many aquariums use filters containing fibers that capture particulates.
• Belt filters recover precious metals during mining.
• Water in an aquifer is relatively pure because it has been filtered through sand and permeable rock in the ground.

Filtration Methods

There are different types of filtration. Which method is used depends largely on whether the solid is a particulate ( suspended ) or dissolved in the fluid.

• General Filtration: The most basic form of filtration is using gravity to filter a mixture. The mixture is poured from above onto a filter medium (e.g., filter paper) and gravity pulls the liquid down. The solid is left on the filter, while the liquid flows below it.
• Vacuum Filtration: A  Büchner flask and hose are used to create a vacuum to suck the fluid through the filter (usually with the aid of gravity). This greatly speeds the separation and can be used to dry the solid. A related technique uses a pump to form a pressure difference on both sides of the filter. Pump filters do not need to be vertical because gravity is not the source of the pressure difference on the sides of the filter.
• Cold Filtration: Cold filtration is used to quickly cool a solution, prompting the formation of small crystals . This is a method used when the solid is initially dissolved . A common method is to place the container with the solution in an ice bath prior to filtration.
• Hot Filtration: In hot filtration, the solution, filter, and funnel are heated to minimize crystal formation during filtration. Stemless funnels are useful because there is less surface area for crystal growth. This method is used when crystals would clog the funnel or prevent crystallization of the second component in a mixture.

Sometimes filter aids are used to improve flow through a filter. Examples of filter aids are silica , diatomaceous earth, perlite, and cellulose. Filter aids may be placed on the filter prior to filtration or mixed with the liquid. The aids can help prevent the filter from clogging and can increase the porosity of the "cake" or feed into the filter.

Filtration vs. Sieving

A related separation technique is sieving. Sieving refers to use of a single mesh or perforated layer to retain large particles​ while allowing the passage of smaller ones. In contrast, during filtration, the filter is a lattice or has multiple layers. Fluids follow channels in the medium to pass through a filter.

Alternatives to Filtration

There are more effective separation methods than filtration for some applications. For example, for very small samples in which it's important to collect the filtrate, the filter medium may soak up too much of the fluid. In other cases, too much of the solid can become trapped in the filter medium.

Two other processes that can be used to separate solids from fluids are decantation and centrifugation. Centrifugation involves spinning a sample, which forces the heavier solid to the bottom of a container. In decantation , the fluid is siphoned or poured off of the solid after it has fallen out of solution. Decantation can be used following centrifugation or on its own.

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Filtration - Process along with Example

Filtration definition.

Filtration is technically defined as the process of separating suspended solid matter from a liquid, by causing the latter to pass through the pores of a membrane, called a filter.

Filtration Examples

The most common example is making tea. While preparing tea, a filter or a sieve is used to separate tea leaves from the water.  Through the sieve pores, only water will pass. The liquid which has obtained after filtration is called the filtrate; in this case, water is the filtrate. The filter can be a paper, cloth, cotton-wool, asbestos, slag- or glass-wool, unglazed earthenware, sand, or any other porous material. Filtration is used in water treatment and sewage treatment.  To have a clear understanding of the matter and its states checkout the  three states of matter.

Filtration Process

The mixtures are of two main types: homogeneous mixtures and heterogeneous mixtures . A homogeneous mixture is a mixture that is uniform throughout. A heterogeneous mixture is a mixture that is not uniform throughout, i.e., ingredients of the mixture are distributed unequally. Air is a homogeneous mixture of different gases, including oxygen, nitrogen, carbon dioxide, and water vapour.

Homogeneous mixtures are sometimes also called solutions; especially when it is a mixture of a solid dissolved in a liquid. An example of a heterogeneous mixture is the mixture of sand in water. On shaking, sand will stay undissolved and are distributed unevenly. The sand particles floating around which will eventually settle to the bottom of the bottle makes it a heterogeneous mixture. Different types of filters are used to purify and for separation of mixtures from the contaminants. Based on the type of contaminant-large or small, filters of different pore sizes can be used, even at home.

Applications of Filtration

Filtration also plays a role in water treatment. The process of filtration can become a costly process when it comes to water treatment and water purification. Maintenance and lack of regulation can become major disadvantages of filtration. Also, water treatment filters are not regulated by any health commission or department, so the effectiveness of filtration and purification can vary widely between manufacturers. But filters have enough advantages to be used as a mechanism of water treatment or purification.

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Centrifugal filtration

What is centrifugal filtration, step by step centrifugal filtration, pros and cons of centrifugal filtration, copy short link.

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Ll educate: introduction to engineering concepts, filtration experiment overview.

While the Laboratory applied its engineering knowledge to problems of filtration, we can study filtration to expand your engineering knowledge. IEEE, the world’s largest technical professional society, has a  Filtration Investigation lesson plan that we’ll use to learn about the engineering process. (Teachers, the IEEE website has resource sheets, information, and activity worksheets for your classroom.) Your challenge is as follows: along with your engineering teammates, design a filtration system to eliminate as much dirt, coffee grinds, or flour as possible from a water sample. This experiment should take about two (2) hours, including planning.

Already you may notice that we are following our engineering design process: we, the clients, have identified a problem for you, the engineers, to solve. Let’s take a moment now to start asking the “whys” before you ask the “hows.”

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Chapter 4: Introduction to Separation Methods

Back to chapter, previous video 4.2: distillation: vapor–liquid equilibria, next video 4.6: recrystallization: solid–solution equilibria.

Filtration is the physical separation of solids from a fluid using a filtration medium.

The filtration medium is chosen depending on the purpose of filtration, quantity, and particle size of the solid.

In general, filtration efficiency increases with particle size.

In simple filtration, the precipitate is first allowed to settle, and the mother liquor is decanted down a glass rod into a funnel fitted with filter paper.

The precipitate is then transferred to the filter paper using a rubber policeman.

Ashless filter paper can be ignited to recover the precipitate, when weighing is required.

Alternatively, a sintered-glass funnel fixed to a Buchner flask, which has a sidearm that can be connected to a vacuum pump, is used to trap the precipitate.

Filtration is a physical separation process that involves passing a suspension through a porous medium to separate solids from fluids. During filtration, solids collect on the porous medium while liquids, also collectively known as the filtrate, pass through. The filtration medium is selected based on the filtration purpose, quantity, and nature of the precipitate. The general criteria for a suitable filtering medium are that it is inert, mechanically strong, nonabsorbent toward dissolved materials and permissive toward rapid filtration.

The simplest filtration apparatus consists of filter paper fitted in a long-stemmed funnel sitting above a beaker. The solution to be filtered is poured down a glass rod onto the filter paper. The filtrate is collected in the beaker, and the solid is retained on the filter paper. Any solid that adheres to the glass rod or the beaker with the original solution is dislodged using a rubber policeman. Because filter paper is hygroscopic, ashless or low-ash filter paper is preferred when weighing is required. Ashless filter paper is also employed in gravimetric procedures that involve igniting the solids before weighing.

Alternatively, the solid can be collected in glass or silica crucibles containing a porous glass disc. The solid is transferred to the crucible fitted into a Buchner flask, and filtration is performed under suction. After filtration, the crucible is dried and weighed directly. The weight difference of the crucible before and after filtration gives the mass of the collected solid.

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Filtration Definition

Filtration is the separating of substances based on their different physical and chemical qualities. Typically, we think of it as the removal of solid particles from a mixture containing both solids and liquids. In this process, we refer to the collected solid material as the residue and the fluid material as the filtrate . Usually, a tool that contains some form of pores is used, which allows the fluid portion, but not the solid portion, to pass through. Different materials are used for the purpose of filtration, including paper, sand, and cloth. Filtration also occurs naturally in our bodies, for example in the kidneys, where the blood is filtered in a process called glomerular filtration .

Types of Filtration

There are many different ways to filter matter, and below are just a few that we can use in the separating of substances.

Vacuum Filtration

In vacuum filtration, a vacuum pump is used to rapidly draw the fluid through a filter. Hirsch funnels and Buchner funnels , which are the same kind of funnel in two different sizes, are used along with filter paper. The funnels have a plate with holes in it, as we can see below, and they are usually used when the substance to be filtered is small in volume.

Centrifugal Filtration

This kind of filtration is done by rotating the substance to be filtered at very high speed. Due to the horizontal rotation, the more dense matter is separated from the less dense matter.

Gravity Filtration

This is where the mixture is poured from a higher point to a lower one. It is commonly done through simple filtration, using filter paper in a glass funnel, where the insoluble solid particles are captured by the filter paper and the liquid goes right through by gravity’s pull. Depending on the volume of the substance at hand, filter cones, fluted filters, or filtering pipets can be used.

Cold Filtration

Cold filtration makes use of very low temperatures, often by using an ice bath. Some substances, such as fatty acid particles, become suspended in the mixture as they cool down, which then allows us to filter them out more easily.

Hot Filtration

This is often used for crystalline compounds that contain impurities. The way this filtration is done is by melting down the crystalline compound, removing the impurities as the substance is still in liquid form, and finally recrystallizing the now pure substance. Often, it is recommended that the apparatus used in this filtration be heated up so that the filtered substance doesn’t crystallize in the funnel and block the flow.

Multilayer Filtration

This can refer to multiple layers of different material, including sand, gravel, or charcoal, where the different layers contain different particle sizes of that material. In this type of filtration, a mixture of liquid and insoluble solid particles is poured over the layers, and the solid particles are caught throughout, resulting in a filtered liquid.

Functions of Filtration

Filtration has many different uses, such as the cleaning of water, like river water, from impurities. It can also be used for sterilization without the use of heat, as long as the filter’s pores are small enough to catch the microorganisms. Keep in mind that this process will not kill the microorganisms since it does not make use of heat.

Related Biology Terms

• Diffusion – The arbitrary spreading of particles from a region where they are at a higher concentration to another where they are at a lower concentration.
• Osmosis – The motion of a solvent through a partially permeable membrane from a region where it is at a higher concentration to where it is at a lower concentration.
• Viscosity – The extent to which a fluid resists flow.

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Filtration is a type of process which separates solid particles and fluid from a mixture with the help of a filter medium that has a complex structure through which only the fluid can pass. Filtration is either a physical, biological or chemical operation. Solid particles that are oversize, cannot pass through the filter medium and the fluid that passes through is known as the filtrate. One problem that sometimes arises in the filtration is that oversize particles may form a filter cake on top of the filter that may block the filter lattice. This filter cake prevents the fluid phase from crossing the filter and is known as blinding.

What is Filtration?

Filtration is a process in which a filter medium is in use to separate solid particles from a liquid or gaseous mixture. The filter allows the fluid to pass through but holds the solid particles. Although filtration is an overused process but still the separation of solid and fluid is imperfect. This is because solids particles get contaminated with some fluid and filtrate also contain some fine particles.

Process Description

1) Filtration is in use to separate solid particles from a fluid in a suspension. This fluid can be a liquid, a gas or a supercritical fluid.

2) Filtration is an important part of chemistry as it deals with the separation of materials of different chemical composition. A solvent is taken into account which has the ability to dissolve one component, while not dissolving the other.

3) Filtration is widely in use as one of the key unit operations in the field of chemical engineering .

4) Filtration is different from sieving, although a filter is in use in both. In sieving, a single perforated layer (a sieve) is used for separation. In the filtration, a multilayer lattice retains those particles that are unable to pass through the barrier channels of the filter.

5) In the case of biological filters, oversize particulates are trapped and ingested and the resulting metabolites is usually released.

Methods of Filtration

A) Hot filtration as the name suggests, mainly is in use to separate solid particles from a hot solution. To prevent the formation of crystals in the funnel and to undergo effective hot filtration, the use of stemless filter funnel is effectively in use. Stemless filter funnel results in the decrease of the surface area of contact between the solution and the stem of the filter funnel. Thus, preventing the issue of re-crystallization of solid in the funnel.

B) In the cold filtration process, an ice bath helps to cool down the solution that’s going to be crystallized rather than leaving it out to cool it down slowly at room temperature.

C) The vacuum filtration process is applied for a small batch of solution in order to quickly dry out small crystals. This method requires a Büchner funnel.

Filter Media

In laboratories two main types of filter media are in use: one is a surface filter, a solid sieve which traps the solid particles, with or without the aid of filter paper (e.g. Belt filter, Büchner funnel,  Cross-flow filters). The second filter is the depth filter, which consists of a layer of granular material that retains the solid particles as it passes (e.g. sand filter). Filter media is usually cleaned by rinsing with solvents or detergents.

Uses of Filtration

• Belt filters to extract precious metals in mining.
• The coffee filter is in use to keep the coffee separate from the grounds.
• In furnaces, filtration prevents the furnace elements from fouling with particulates.
• Air filters help to remove airborne particulate matter in building ventilation systems and in many industrial processes.
• Oil filter is useful in the automobile industry, often as a canister or cartridge.

FAQs about Filtration

Q.1. What is a common issue for filtration in water treatment?

Answer – Dirty filter is a common issue for filtration in water treatment. Dirty filter chemicals and heavy metals find their way into drinking water. Different types of water filtering systems have their own requirements for maintaining the filter.

Q.2. What is the disadvantage of filtration?

Answer – The main disadvantages of barrier-based filtration are, replacement and disposal costs. When this type of filter gets blocked by waste particles, it needs to be replaced which is cost-effective.

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Make a water filter

This fun science experiment turns dirty water clean. (Kind of.)

How do you clean up dirty water?

Not with soap! You need a filter, a device that removes impurities, like dirt, from water. The filter you’ll make here—with the help of an adult—is a super strainer, and it’ll help you clean up your act.

Ask a grown-up to cut the bottle in half. Then flip the bottle's top half over and put it in the bottom, so the top looks like a funnel. You'll build your filter in the top part.

Place the coffee filter (or bandanna, sock, etc.) at the bottom of your filter.

Add cotton balls, charcoal, gravel, sand, and / or other materials in layers. You can use just one of them or all of them. Tip: Think about which order to add them. Bigger filter materials usually catch bigger impurities.

Write down which filter materials you used and in what order you layered them.

Stir your dirty water and measure out a cup of it.

Get your timer ready!

Pour a cup of dirty water into your filter. Start the timer as soon as you begin pouring.

Time how long it takes for all the water to go through the filter. Then write down how long it took.

Carefully scoop out the filter materials, one layer at a time. What did each layer take out of the water?

Experiment! Clean the bottle and try again. Put the filter materials in a different order each time, and time each experiment. What do you discover?

WHAT'S GOING ON?

The slower, the better! The longer it takes for water to move through a filter, the cleaner it gets. Water slips easily through the filter materials, but bigger gunk, like dirt, gets trapped. The filter materials usually get finer and finer, so they can catch whatever was missed earlier. Activated charcoal can be near the end of the water’s path, because it uses an electrical charge to grab particles too small for us to see.

Your filtered water is not clean enough to drink. But a plant will love it!

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Filtration: Definition, Process, Diagram and Examples

Filtration is a method to separate the components of a mixture where the solvent part is liquid and the solute is an insoluble solid. Let’s know more about Filtration Definition, Process, Application and examples in detail below.

In simple words, Filtration is the process in which solid particles in liquid or gases are removed by the filter that allow the passes of liquid but blocks the passage of solid. The mechanism of “filtration” can be mechanical, biological, or physical.

Filtration Definition

Filtration is defined as the process in which solid particles in liquid or gases are separated by the filter that only allow the liquid to pass through it but blocks the passage of solid.

This process is carried out using a filter medium, for instance, filter paper. The pores of the filter medium are bigger as compared to the solvent particle but are smaller compared to the solute particle, so they allow only solvent particles to pass through them the solute particle is left on the other side making the solution free from the insoluble solute.

The principle of filtration is based on the difference in sizes between the particles.

Filtration Process

The process of filtration uses the concept of difference in the particles. We have two types of mixtures 

• Heterogenous Mixture
• Homogenous Mixture

We define a heterogeneous mixture as a mixture in which the solute particle is not evenly distributed in the solvent phase. Such as sand in the water is an example of a heterogeneous mixture.

On the other hand, a homogeneous mixture is a mixture in which the solute particle is evenly distributed in the solvent phase. A brine solution is an example of a homogenous mixture. Homogenous mixtures are also called solutions. Various types of processes are used for the filtration.

In general, the filtration process uses the concept, we take a filtration membrane such that it allows only a specific size particle to move through it making the solution at one end free from the insoluble solute particle. We can understand this using the example, suppose we have to filter sand and water.

We use a muslin cloth at the mouth of the container containing the sand in water solution. After that, we allow the solution to pass through the muslin cloth which only allows water to pass through it separating the sand from the sand and water solution. We can also use filtration paper in place of muslin cloth as the filtration membrane.

Filtration Diagram

Below is the filtration diagram, which will we can understand the filtration process. In this process we allow the mixture to pass through the filter paper which separates the insoluble solid from the solution.

Here the filter paper allows the liquid to pass through it but stops the bigger solid particles which are then removed manually and the solution is filtered in this way. 

We can easily filter any of the solutions, if we have

• Filter Medium (Filter Paper)
• Slurry or Residue (fluid with suspended solids)
• Filtration Driving Force (pressure, force, gravity, etc)
• Filtration Device that holds the filter medium and filtrate.

Filtration Examples

Filtration is one of the most important techniques for the Separation of Mixtures in a laboratory, it is also a common process happening in our everyday life like:

• When making coffee, hot water is filtered through the ground coffee and a coffee bean. The filtrate is the coffee in liquid form. Using a tea ball or a tea bag (paper filter) for brewing tea is very also an example of filtration example.
• A kidney is a biological filter that is used to filter the human blood.
• HEPA filters are used by various vacuum cleaners and air conditioners to filter out dust and pollen from the air.
• Filters with particulate-capturing fibers are commonly used in aquariums.
• During mining, belt filters extract precious metals.
• Sand and permeable rock in the ground filtered the water which is then stored in the aquifer and then used as groundwater.

Applications of Filtration

Some applications of separation by filtration method are mentioned below.

• Filtration of Tea or Coffee using a Sieve.
• Separation of chalk powder and water from their solution.
• Vacuum cleaners are fitted with filters in order to absorb dust particles.
• Filtration of sand particles from water or chalk powder.
• The wastewater treatment plant uses the filtration technique to filter the sewage.
• Filtration techniques are used in the metallurgical process to remove the slag.
• Air filters are used in automobiles and in factories to remove harmful particles from the smoke.
• The treatment of water uses filtration techniques.
• Blood filtering in kidneys is another application of the filtration technique.
• Water Purification
• Pure and Impure Substance
• How to Separate a Mixture of Solid and Liquid
• Homogeneous and Heterogenous Mixture
• Separation By Suitable Solvent

Filtration – FAQs

What is filtration .

Filtration is a separation technique that uses a porous medium that retains the solid substance but allows the fluid to penetrate through it. It is the process of removing insoluble substances from the solution. 

How to Filter Water at home?

We use various techniques to filter water at home. Some of the important methods used to filter water are, Use of Filtration Membrane (Muslin Cloth, etc) Bolling of Water. Use of Chemicals such as Chlorine, Bleaching Powder, etc. Use of RO (Reverse Osmosis) Filter

Which type of Mixture can be Separated by Filtration?

A mixture that contains a liquid and an insoluble solid can be Separated by Filtration.

What is the Principle of Filtration?

The size of the solute and the solvent particle differs a lot and this concept is used as the principle of filtration. That the difference in size allows only the smaller particles to move from the filtration membrane.

Who Filters the Blood in the Body?

The blood in the human body is filtered through the kidneys. The filtration unit of the kidney is called the nephron , which is responsible for the filtration of blood in the human body.

What is Filtration Membrane?

Filtration membranes are living or non-living membranes formed by either organic or inorganic materials that are used to separate dissolved materials or solutes from a true solution or from a colloidal solution.

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Filtration is a technique used either to remove solid impurities from an organic solution or to isolate an organic solid. The two types of filtration commonly used in organic chemistry laboratories are gravity filtration and vacuum or suction filtration.

Gravity Filtration

Gravity filtration is the method of choice to remove solid impurities from an organic liquid. The impurity can be a drying agent or an undesired side product or leftover reactant. Gravity filtration can be used to collect solid product, although generally vacuum filtration is used for this purpose because it is faster.

A filtration procedure called "hot gravity filtration" is used to separate insoluble impurities from a hot solution. Hot filtrations require fluted filter paper and careful attention to the procedure to keep the apparatus warm but covered so that solvent does not evaporate. Hot gravity filtrations are no longer included in the routine procedures for the experiments in the organic chemistry teaching labs. If you need to do such a filtration, read the procedure in the Handbook and consult your TA.

To perform a standard gravity filtration , first select the size of filter paper that, when folded, will be a few millimeters below the rim of your stemmed funnel . Fold the paper into a cone by first folding it in half, and then in half again, as shown.

Next, support the glass funnel in a ring or place it in the neck of an Erlenmeyer flask. Wet the filter paper with a few milliliters of the solvent to be used in the following procedure. Wetting the paper holds it in place against the glass funnel. Pour the mixture to be filtered through the funnel, in portions if necessary.

Fluted filter paper is often better for gravity filtration with organic solvents. A diagram of how to fold fluted filter paper is shown below.

Vacuum Filtration

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Source: Surasit Rojtrairat / Shutterstock.com

How to teach evaporation, filtration and crystallisation

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David Paterson discusses ideas for enhancing practical work on separating mixtures by filtration, evaporation and crystallisation

The physical processes of separating mixtures by filtration, evaporation and crystallisation are key to many industrial and research purposes. For example, water purification, edible salt production and pharmaceutical formulation require aspects of these techniques. Research chemists preparing new substances will frequently use these processes. Substances require purification to allow for further synthetic steps and for structural analysis.

Source: Clockwise from top left: Dmitry Kalinovsky; Surasit Rojtrairat; Mr. 1; Dmitry Kalinovsky / Shutterstock.com

Industrial and research uses of evaporation, filtration and crystallisation. Clockwise from top left: filtration in water purification; evaporation in salt production; a rotary evaporator in a chemical research laboratory; pharmaceutical formation

Underlying principles

The science of separating substances is based on the principles of purity, physical properties and solutions. For example, chromatography is a separation process based on solubility 1 and distillation is based on boiling point. 2 This article looks at separation by particle size (filtration) and removal of volatile solvents (evaporation and crystallisation).

The science of separating substances is based on the principles of purity, physical properties and solutions. For example, chromatography is a separation process based on solubility 1 and distillation is based on boiling point . 2 This article looks at separation by particle size (filtration) and removal of volatile solvents (evaporation and crystallisation).

Underlying all separation techniques are the concepts of purity and the difference between mixtures and compounds. You can discuss purity using everyday drinks as a context. Students could analyse the labels of bottled water or juices that claim to be ‘100% pure’ to show they contain various substances. Among other components, mineral waters contain varying levels of dissolved salts, and orange juices contain sugars, protein and vitamin C.

Source: Royal Society of Chemistry

The key concepts involved in separation by evaporation, filtration and crystallisation

Practical activities to help students distinguish mixtures from compounds include the classic iron sulfide synthesis reaction. 3 The reaction of aluminium with iodine also provides a memorable demonstration. 4 Students could repeat the simple separations of mixtures they have carried out at primary or 11–14 level. For example, separating iron filings from sand 5 or breakfast cereal. 6

Practical activities to help students distinguish mixtures from compounds include the classic iron sulfide synthesis reaction . 3 The reaction of aluminium with iodine also provides a memorable demonstration. 4 Students could repeat the simple separations of mixtures they have carried out at primary or 11–14 level. For example, separating iron filings from sand 5 or breakfast cereal . 6

You can easily demonstrate the importance of particle sizes by sieving a mixture of rice and caster sugar. Or, show the volatility of substances by using a few drops of propanone on a watch glass in different environments. 7

Use the context of the formation of saturated solutions of ammonium chloride to discuss the concepts of solution and saturation. 8 Try this activity both qualitatively and quantitatively, introducing concentration and solubility calculations in later years. The Chemical misconceptions resources 9 cover the differences between elements, compounds and mixtures. 

A relevant context to engage students, and link to social and economic aspects of chemistry, is the separation of metals ores. Rocks are mixtures of different minerals, and must be separated to concentrate and eventually purify the desired metal. Physical processes such as crushing, sifting and flotation separate the components. 10 The recycling industry uses similar processes to separate metals, glasses and plastics in household waste, 11 and when recycling cars.

A relevant context to engage students, and link to social and economic aspects of chemistry, is the separation of metals ores. Rocks are mixtures of different minerals, and must be separated to concentrate and eventually purify the desired metal. Physical processes such as crushing, sifting and flotation separate the components . 10 The recycling industry uses similar processes to separate metals, glasses and plastics in household waste, 11 and when recycling cars.

Techniques through the curriculum

Students learn the techniques of evaporation, filtering and crystallisation from primary school through to post-16 education.

Students learn the techniques of evaporation, filtering and crystallisation from primary school through to post-16 education (see table). Download a detailed table of links to the national curriculum and exam specifications from the Education in Chemistry website: rsc.li/EiC418sep2.

Specification links

Download a table of links to exam specifications and the English national curriculum ( MS Word or pdf )

Evaporation

Evaporation requires heat (or air movement above the sample) to drive off a volatile solvent. If the substance is a solid mixed in a solvent, begin by filtering (or decanting). If the substance is dissolved in a solvent, then use crystallisation. 

There are various techniques for heating a substance. For example, direct heating with a Bunsen burner or a sand bath, or by placing an evaporating basin over a beaker of heated water. Students could discuss and evaluate the different methods. For example, direct heating is quicker, but can superheat the solution, potentially degrading the solute and leading to spitting of the solid. You can make links to the difference between distillation via direct heating and steam distillation, and the use of the latter in separating fragile components. 2

There are various techniques for heating a substance. For example, direct heating with a Bunsen burner or a sand bath, or by placing an evaporating basin over a beaker of heated water. Students could discuss and evaluate the different methods. For example, direct heating is quicker, but can superheat the solution, potentially degrading the solute and leading to spitting of the solid. You can make links to the difference between distillation via direct heating and steam distillation, and the use of the latter in separating fragile components . 2

Students could annotate diagrams of the different methods to consolidate their understanding and help them learn the names and diagrams of the various laboratory apparatus.

Download a set of labelled apparatus diagrams and a worksheet without labels for use in your classroom from the Education in Chemistry website: rsc.li/EiC418sep2.

Download a set of labelled apparatus diagrams ( MS Word or pdf ) and a worksheet without labels for use in your classroom ( MS Word or pdf ).

Having a set of questions ready to ask can help focus students on the purpose and practicalities of the techniques (see table 1).

Having a set of questions ready to ask can help focus students on the purpose and practicalities of the techniques.

Filtration requires various pieces of glassware, which can lead to student confusion about what needs placing where, and what is poured where and when. It is worth re-demonstrating and explicitly naming the apparatus to reinforce this important knowledge. Most students will be able to carry out filtration without further guidance, although there is a range of common issues (see table).

Filtration requires various pieces of glassware, which can lead to student confusion about what needs placing where, and what is poured where and when. It is worth re-demonstrating and explicitly naming the apparatus to reinforce this important knowledge. Most students will be able to carry out filtration without further guidance, although there is a range of common issues.

Crystallisation

Crystallisation occurs when the solution solvent evaporates, and the concentration of the solute reaches saturation point. At this stage, the solute begins to precipitate out of solution. Under the right conditions, generally slow evaporation and a clear solution, the solute will crystallise. You can easily demonstrate the principles of crystallisation with saturated solutions of sodium acetate. 12 Teachers commonly use this activity to model the freezing process, and it helps tackle misconceptions around the energetics of freezing, particularly the exothermic nature of freezing (bonds being formed). A similar activity suitable for a student practical is freezing super-cooled sodium thiosulfate. 13

Crystallisation occurs when the solution solvent evaporates, and the concentration of the solute reaches saturation point. At this stage, the solute begins to precipitate out of solution. Under the right conditions, generally slow evaporation and a clear solution, the solute will crystallise. You can easily demonstrate the principles of crystallisation with saturated solutions of sodium acetate. 12 Teachers commonly use this activity to model the freezing process, and it helps tackle misconceptions around the energetics of freezing, particularly the exothermic nature of freezing (bonds being formed). A similar activity suitable for a student practical is freezing super-cooled sodium thiosulfate . 13

Recrystallisation is a key practical skill required at A-level. Benzoic acid is a useful substance to demonstrate and practise the technique. Benzoic acid will dissolve in hot water and crystallise when the water cools, potentially reducing the need to carry out recrystallisation using organic solvents. 14 This can be particularly useful if you have limited access to fumehoods.

You can put recrystallisation in the wider context of organic synthesis by synthesising and purifying aspirin 15 or paracetamol. 16 Use videos to give your students some pre-lab support with the technique. 17

You can put recrystallisation in the wider context of organic synthesis by synthesising and purifying aspirin 15 or paracetamol . 16 Use videos to give your students some pre-lab support with the technique. 17

Crystallisation could form a project either for extension within class, or perhaps as an activity for a science club. The Royal Society of Chemistry ran a global experiment in 2014 looking at the art of crystallisation. The project suggests various different salts, including potassium nitrate and alum. The resources include a useful crystal shape classification. 18 Further ideas and resources are available from the British Crystallographic Association. 19

Bring techniques together in context

In reality, most separation techniques are rarely used in isolation. Separation usually involves multiple steps and techniques to obtain a pure product. However, you can use specific contexts to show how the individual techniques are optimised to obtain the desired results.

The production of sweets is a good example. 20 Aqueous sugar solutions at different concentrations have different properties. As a sugar solution is boiled, the water evaporates and the concentration of the sugar increases. As the boiling point is dependent on sugar concentration, the temperature of the solution increases steadily as concentration increases, from the ‘soft ball’ (fudge) concentration (85%) to ‘hard crack’ (toffee, 99%). When a saturated solution of sugar is cooled slowly, sugar crystals will form. The initial crystallisation is slow, but you can speed it up by adding a seed crystal suspended in the solution by a cotton thread. Once crystallisation has started, it proceeds quickly over the next couple of days. 21

The production of sweets is a good example . 20 Aqueous sugar solutions at different concentrations have different properties. As a sugar solution is boiled, the water evaporates and the concentration of the sugar increases. As the boiling point is dependent on sugar concentration, the temperature of the solution increases steadily as concentration increases, from the ‘soft ball’ (fudge) concentration (85%) to ‘hard crack’ (toffee, 99%). When a saturated solution of sugar is cooled slowly, sugar crystals will form . The initial crystallisation is slow, but you can speed it up by adding a seed crystal suspended in the solution by a cotton thread. Once crystallisation has started, it proceeds quickly over the next couple of days. 21

A more complex context, but one that can lead to many interesting discussions, is chocolate. Multiple crystal forms exist, providing a complex phase diagram and many extension opportunities for keen or high attaining students. 22 The overlap of chemistry, cooking and business makes studying chocolate a potentially interesting cross-department project. 23

A more complex context, but one that can lead to many interesting discussions, is chocolate. Multiple crystal forms exist , providing a complex phase diagram and many extension opportunities for keen or high attaining students. 22 The overlap of chemistry, cooking and business makes studying chocolate a potentially interesting cross-department project. 23

Bringing techniques together in one activity

Source: David Paterson

Comparison of crystallisation – in the left hand evaporating basin crystals took two days to completely form. Right hand watch-glass (microscale) – crystals completely formed within ten minutes

Making hydrated copper sulfate crystals from copper oxide and sulfuric acid requires all of the filtration, evaporation and crystallisation techniques. 24 React copper oxide with hot sulfuric acid. Filter the mixture to remove unreacted copper oxide, then heat the filtrate to evaporate off about half the water. Leave the concentrated solution in a warm spot to allow the blue hydrated copper sulfate solution time to slowly crystallise. Filter and dry the crystals.

Making hydrated copper sulfate crystals from copper oxide and sulfuric acid  requires all of the filtration, evaporation and crystallisation techniques. 24 React copper oxide with hot sulfuric acid. Filter the mixture to remove unreacted copper oxide, then heat the filtrate to evaporate off about half the water. Leave the concentrated solution in a warm spot to allow the blue hydrated copper sulfate solution time to slowly crystallise. Filter and dry the crystals.

Microscale synthesis of copper sulfate – copper oxide and sulfuric acid in a glass vial in a sand bath

There are some issues with the traditional way this practical is carried out, 25 including the need to heat large volumes of acid, the slow evaporation step and slow crystallisation. A microscale alternative allows students to get from reagents to crystals within one lesson. 26 Heat the sample using a sand bath, both to increase the rate of the reaction and also to evaporate some solvent from the copper sulfate solution. Filter the sample through mineral wool in a syringe. Aside from the speed advantages, students can work individually, giving them time to focus on improving their manual dexterity.

There are some issues with the traditional way this practical is carried out , 25 including the need to heat large volumes of acid, the slow evaporation step and slow crystallisation. A microscale alternative allows students to get from reagents to crystals within one lesson. 26 Heat the sample using a sand bath, both to increase the rate of the reaction and also to evaporate some solvent from the copper sulfate solution. Filter the sample through mineral wool in a syringe. Aside from the speed advantages, students can work individually, giving them time to focus on improving their manual dexterity.

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Resources recommended in this article

• An  article on chromatography , covering the underlying chemistry, progression through the curriculum and practical suggestions.
• An  article on distillation .
• An u pdated version of the classic iron sulfide synthesis , with small quantities and lower risks (CLEAPSS L195 Safer chemicals, safer reactions – Experiment 9.2).
• A  spectacular demonstration on the properties of elements and compounds with aluminium iodide.
• A  simple practical on separating salt, sand and iron filings based on physical properties.
• A  simple practical or demonstration , showing the presence of iron in breakfast cereals, involving separation by magnets.
• A  practical investigation on the factors that affect the evaporation of propanone .
• A  practical investigation on the factors the affect the solubility of ammonium chloride .
• A high quality  worksheet to probe students understanding of the differences between elements, compounds and mixtures .
• Details of  the extraction of gold from ores .
• A  short video on a household waste recycling plant in Norfolk, UK .
• The formation of ‘ hot-ice’ stalagmites using super-saturation sodium acetate solutions .
• Supercooling  sodium thiosulfate solution can be used to provide context for crystallisation.
• A  full lesson kit on the recrystallization of benzoic acid .
• A  curriculum resource for post-16 chemistry and science courses on the synthesis, purification and characterisation of aspirin .
• A  curriculum resource for post-16 chemistry and science courses on the synthesis, purification and characterisation of paracetamol .
• An  interactive lab primer on carrying out recrystallization .
• Full  resources for the ‘art of crystallisation’ global experiment , including videos and practical instructions.
• A website about the International Year of Crystallography, 2014. (website no longer available)
• An  article on the chemistry behind the manufacture of sweets , which includes links to videos and useful particle diagrams.
• Simple  instructions on how to make sugar crystals .
• A  website with plenty of details on the chemistry and culinary aspects of chocolate production .
• More  details on how chocolates are made .
• An  improved method for the classic formation of hydrated copper sulfate crystals [£], which doesn’t involve boiling sulfuric acid.
• A  traditional method for synthesising hydrated copper sulfate crystals .
• A  microscale version of the hydrate copper sulfate synthesis that allows students to go from reagents to crystals in one lesson.

Curriculum and specification links

Apparatus diagrams - with labels, apparatus diagrams - without labels.

More David Paterson

Planning for safe practical work (CLEAPSS)

Enhance students’ learning and development with digital resources

Use AI to successfully assess students’ understanding

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