Separation Techniques in Science

Separation Techniques

• Sieving, Decanting, Magnets, Filtration, Evaporation (and crystallization), Distillation, and Chromatography are separation techniques.

Floatation

• Plastic floats on water and can be scooped out with a net.

Separating Funnel

• Separating funnels are used to separate two immiscible liquids of different densities.
• The less dense liquid floats on top.
• For example, oil floats on water.
• You can separate oil and water by opening the tap and letting the water (the more dense liquid) out into a beaker.
• Use a different beaker to collect the oil.

Centrifuge

• A centrifuge is a machine that creates a rotational force, used to separate a mixture containing particles of different densities.
• The centrifuge forces the more dense particles to the bottom of the tube, forming a pellet.
• The remaining solution on top is called the supernatant.
• The supernatant can be removed off the top with a pipette and placed into a new centrifuge tube.
• The new tube can be spun at a faster speed to further separate the particles remaining in the mixture if they have different densities.

Centrifuging Blood

• If you centrifuge blood, the red blood cells will form a pellet at the bottom of the tube.

Centrifuging Milk

• Centrifuges can be used to separate cream from milk.
• Before the invention of centrifuges, cream was skimmed off the top of milk after it had been sitting for a while.
• Centrifuges make separating cream from milk faster and easier.

Separation Techniques

• Sieving: Separates solids of different sizes
• Decanting: Separates a liquid from a solid by pouring off the liquid carefully. Separating funnel
• Magnets: Separates magnetic solids from non-magnetic materials.
• Filtration: Separates an insoluble solid from a liquid using a filter paper.
• Evaporation: Separates a soluble solid from a liquid by heating the liquid.
• Crystallization: Recrystallized solid is separated from the liquid by heating the solution, evaporation, and cooling.
• Distillation: Separates liquids with different boiling points.
• Chromatography: Separates mixtures based on the different rates at which components move with the mobile phase.
• Floatation: Separates solids based on their density, using a liquid where the solid floats.
• Separating funnel: Separates two immiscible líquidos based on density. The less dense liquid forms a layer on top of the denser liquid.
• Centrifuge: Spins a mixture at high speed, separating components based on their density. Denser particles form a pellet at the bottom, and the less dense liquid forms a supernatant layer.
• Centrifuging applications: Separating blood plasma, cream from milk, and separating mixtures of different densities.

Separating funnel

• Used to separate two immiscible liquids of different densities.
• The less dense liquid floats on top.
• Oil and water are immiscible, oil floats on water.
• To separate, open the tap and let out the lower layer of water (more dense)
• Then collect the oil (less dense).

Centrifuge

• A machine that spins a mixture at high speed.
• Used to separate a mixture containing particles of different densities.
• Denser particles form a pellet at the bottom.
• The remaining solution on top is called the supernatant.
• In centrifugation, the supernatant can be spun at a faster speed to further separate the remaining particles if they have different densities.
• Centrifuging blood: Separates blood components, including red blood cells, white blood cells, and platelets.
• Centrifuging milk: Separates cream (fat) from milk.
• Centrifuging mixtures: Separates different substances based on their densities.
• The mixture is spun, and the largest particle forms a pellet first.
• Each subsequent spin separates the next largest particle at the bottom.

Separating Funnel and Centrifuge Notes

• 1: Describe how to separate oil and water using a separating funnel. Draw a labelled diagram.
• 2: Explain how a centrifuge works to separate mixtures.
• 3: Describe what happens when freshly collected blood is put in a centrifuge and why this happens.
• 4: Describe what happens when freshly collected milk is put in a centrifuge and why this happens.
• 5: Draw a sketch of a centrifuge tube after a mixture has been centrifuged, label the pellet and the supernatant.

Separation Techniques

• Sieving separates mixtures of different sized particles.
• Decanting separates mixtures of a liquid and a solid where the solid settles at the bottom.
• Magnets separate mixtures containing magnetic materials, like iron.
• Filtration separates mixtures of solids and liquids, using filter paper.
• Evaporation separates mixtures of a dissolved solid and a liquid, the liquid evaporates, leaving the solid behind.
• Distillation separates liquids with different boiling points, the liquid with the lower boiling point evaporates first.
• Chromatography separates mixtures based on the different rates at which substances move through a stationary phase.
• Floatation separates mixtures based on the densities of the components.
• Separating Funnel separates immiscible (non-mixing) liquids with different densities, it allows the denser liquid to be drained out.
• Centrifugation separates mixtures based on the densities of the components.

Centrifuges

• Centrifuges rotate at high speeds, causing denser particles to settle at the bottom, creating a pellet.
• The liquid on top is called the supernatant.
• Centrifugation can be used multiple times to separate particles with different densities.
• Freshly collected blood in a centrifuge would separate into red blood cells (pellet), white blood cells and platelets (pellet), and plasma (supernatant).
• Freshly collected milk in a centrifuge would separate into cream (less dense), and skimmed milk (more dense).
• The supernatant from the first spin of a centrifuge can be spun again to further separate the particles remaining in the mixture.
• In a centrifuge tube after a mixture has been centrifuged, the pellet is found at the bottom, and the supernatant is found on top.

Mixtures

• Pure substances are difficult to break down, mixtures are easier.
• Pure substances are elements and compounds
• Mixtures are either homogenous or heterogenous

Homogenous Mixtures

• Particles are spread evenly
• Examples: nitrogen and oxygen in air, steel, vinegar, brass, black coffee, natural gas

Heterogenous Mixtures

• Different components are scattered unevenly
• Examples: salad, chocolate chip cookies, soda with ice.

Types of Mixtures (By particle size)

• Solutions contain very small particles (less than 1000nm)
• Colloids contain particles too small to settle or be removed by filtering
• Suspensions contain larger particles that will settle or be removed by filtering

Solutions

• Appear clear
• Light beam will not be visible when shone through a solution

Colloids

• Appear cloudy
• Light beam will be visible when shone through a colloid
• Examples: milk, mist, cappuccino froth, whipped cream, ice-cream, paint

Suspensions

• Appear cloudy
• Light beam will be visible when shone through a suspension
• Examples: mud mixed with water

Types of Colloids

• Foams - gas trapped within a liquid or solid (e.g. shaving cream)
• Aerosols - liquid or solid particles dispersed in a gas (e.g. fog, smoke)
• Emulsions - two or more insoluble liquids (e.g. homogenized milk, mayonnaise)
• Gels - solid particles in a liquid medium (e.g. gelatin)
• Sols - liquid particles in a solid medium (e.g. ink)

Emulsions

• One liquid is able to spread evenly through another liquid instead of settling
• Unhomogenized milk is not an emulsion, homogenized milk is
• Emulsifiers keep immiscible liquids dispersed
• Examples: mayonnaise, moisturizer, salad dressing

Immiscible Liquids

• Do not mix
• Water and oil are immiscible
• Emulsifiers are chemicals added to immiscible liquids to keep them dispersed
• Lecithin in egg yolk is the emulsifier in mayonnaise

The Tyndall Effect

• The scattering of light by particles present in a colloid or suspension
• The only difference between a colloid and a suspension is the size of the particles
• Colloids have particles between 1-1000 nanometers
• Suspensions have particles from 10-1000 micrometers

Chromatography

• Stationary phase is the paper
• Mobile phase is the water
• Solvent front is the term used to describe how the solvent moves up the stationary phase
• The baseline should be drawn with a pencil below the spots to avoid it dissolving in the solvent
• Dyes that move a long way up the stationary phase have a high solubility in the solvent
• Dyes that do not move very far up the stationary phase have a high affinity for the stationary phase
• The solvent front is drawn at the point where the solvent has travelled furthest
• Chromatograms for two different black ink pens will have different numbers and positions of spots because the dyes in the ink will be different
• Rf value is calculated by the following formula : Rf=distancetravelledbysubstancedistancetravelledbysolventR_f = \frac{distance travelled by substance}{distance travelled by solvent}Rf​=distancetravelledbysolventdistancetravelledbysubstance​
• The Rf values will change if a different solvent is used
• Rf values for the spots X, Y and Z are:
  • Rf X = 0.86
  • Rf Y = 0.67
  • Rf Z = 0.53

Decanting

• Decanting is a technique to separate a dense, insoluble solid from a liquid.
• The solid settles at the bottom of the container forming a sediment.
• The liquid is carefully poured into a new container leaving the solid behind.
• Decanting is only useful if the solid particles readily settle to the bottom.
• It is commonly used when pouring some wines after the sediments have settled.

Sieving

• Sieving separates a dry mixture of two solids with different particle sizes.
• A sieve is chosen with holes that allow one particle through but not the other.
• It is used to separate hazelnuts, peppercorns and sugar.
• It is also used to separate pasta from the water it was boiled in.

Filtration

• A special form of sieving that separates very fine solid particles from liquid or gas mixtures.
• Filter paper with fine pores acts as the sieve.
• It separates an insoluble solid from a liquid.
• Sand does not dissolve in water and is considered insoluble.
• When filtering sand and water, the sand (residue) stays behind in the filter paper, while the water (filtrate) passes through.
• Filtration is used to separate insoluble particles that are too large to pass through the filter paper.

Suspensions

• A mixture of very small pieces of solid mixed in a liquid but not dissolved.
• The solid particles will separate from the liquid and either fall to the bottom or rise to the top.
• Examples include sand in water and chalk in water.
• The solid particles will sink to the bottom forming a sediment.
• Suspensions can separate quickly or stay suspended for a longer time depending on their composition.

Solutions

• When something dissolves, it is considered soluble.
• The liquid that dissolves the solid is called the solvent.
• The solid that dissolves is called the solute.
• The new name for the liquid mixture with the dissolved solute is a solution.
• Salt dissolves in water making a salt water solution.
• Salt is the solute and water is the solvent.

Test your knowledge on various separation techniques used in science, such as filtration, distillation, and chromatography. This quiz covers methods for separating different substances effectively and their applications in real-life scenarios. Challenge yourself to understand the principles behind techniques like centrifugation and the use of separating funnels.