In our previous class, we learnt that mixtures can be separated by physical means. Separation techniques are physical methods used to separate chemicals or substances from their corresponding mixtures. Mixtures are separated by using the physical properties of the individual constituents. These methods include:

This method is used to separate magnetic substances from non-magnetic substances. It takes advantage of the magnetic properties of the constituent of the mixture. A solution of iron fillings and sulphur can be separated using this method. It is used in the steel industry and also to remove magnetic impurities from tin ore.

This method is used to separate solids of different sizes from a solid mixture. This technique uses size as its medium for separation. A sieve is used to separate solid particles the tiny solid particles pass through the seize which is made up of tiny holes while the larger particles remain in the sieve. This method is used in Cassava processing factories to prepare garri, to sift rice, flour sieving, etc

This method is used to separate substances that sublime on heating from those that do not in a mixture. Sublimation is the transition of a solid directly to gaseous state on heating without passing through the liquid state. camphor, anthracene, naphthalene, dry ice, iodine, ammonium chloride, menthol, sulphur, benzoic acid, can be separated from their corresponding mixtures by sublimation.

This method is used to separate an insoluble solid from a mixture of liquid or gas through the use of a filtration apparatus. For instance, a mixture of sand and water can be separated by filtration. It is also used to separate a mixture of an insoluble solid from a soluble solid in its solution. For example calcium carbonate can be separated from a solution of ammonium, sodium and potassium salts through filtration. This separation technique takes advantage of the solubility of the individual constituents.

This method is used to separate a mixture of two miscible(mixed together) liquids with a far range of boiling points. Simple distillation involves heating the liquid mixture to the boiling point
and immediately condensing the resulting vapors.It is used to recover a solvent from its solution. For instance, Ethanol with a boiling point of 78°C can be separated from its mixture with water (Boiling point of 100°C) via simple distillation. This method takes advantage of the difference in range of boiling points. It is used in brewery industries for the purification of alcohol.

This method is used to separate a mixture of miscible liquids with closely ranged boiling points. Fractional distillation is the separation of a mixture into its component parts, or fractions. Chemical compounds are separated by heating them to a temperature at which one or more fractions of the mixture will vaporize. This is usually done using a fractionating column. This method used close range differences in boiling point as it's criteria for separation. It is used industrially in the separation of crude oil components and also to separate oxygen or nitrogen from liquid air.

Decantation is the process of separation of liquids from solid and other immiscible (non-mixing) liquids, by removing the liquid layer (less dense) at the top from the layer of solid or liquid(denser) below. The process can be carried out by tilting the mixture to pour out the top layer. This is an ineffective means of seperation as it doesn't give a pure sample. It uses Density as the criteria for seperation. A mixture of oil and water can be separated using this method. Also a mixture of sand and water can be seperated by decantation.

Evaporation to dryness can be used as a separation method to separate components of a homogeneous mixture with a dissolved solid in a liquid. The liquid is evaporated, meaning it is convert from its liquid state to gaseous state. This often requires heat. Once the liquid is completely evaporated, the solid is all that is left behind. Salt can be seperated from its solution via evaporation. It is used to recover a solute from its solution. This method leads to the complete loss of the solvent. This method uses differences in boiling point and vapor pressure as the criteria for separation. A solution of salt (B.p 1465°C) and water (B.p 100°C) can be seperated by evaporation to dryness.

Crystallization is a technique for purification of the substance. It is a technique that separates a solid which decomposes on heating from its solution. The process in which the solid dissolve in the liquid arranges itself in well-defined 3-D lattice structures called the crystal is called crystallization. This method is used where purity of the product is important. The crystallization of salt occurs when the liquid in the solution tends to evaporate and the temperature of the solution decreases making the nucleus of the crystal of the salt grow with the passage of time. it is used in the manufacture of drugs and sugar. Some salts can contain water of crystallization e g.
Copper(II) tetraoxosulphate( VI).pentahydrate (CuSO₄.5H₂O), Iron(II)tetraoxosulphate(VI). (FeSO₄.7H₂O) etc.

This method of separation is used to separate the constituents of a mixture by taking advantage of their different rate of movement in a solvent over an adsorbent medium. It is used to separate colored substances.

Chromatography is a technique used to separate and analyze mixtures of compounds based on their differential affinities for a stationary phase and a mobile phase. It has various applications in science, industry, and research.

• Gas Chromatography (GC): This type of chromatography uses a gaseous mobile phase to separate volatile compounds based on their interaction with a stationary phase.
• Liquid Chromatography (LC): In this technique, a liquid mobile phase is used to separate compounds based on their interaction with a stationary phase.
• Thin-Layer Chromatography (TLC): TLC involves placing a sample on a thin layer of adsorbent material, which is then developed using a liquid solvent to separate compounds.
• High-Performance Liquid Chromatography (HPLC): HPLC is a more advanced form of liquid chromatography that uses high pressure to achieve faster and more efficient separations.
• Ion Exchange Chromatography: This method separates compounds based on their ionic interactions with a charged stationary phase.
• Affinity Chromatography: Affinity chromatography utilizes specific interactions between molecules, such as antigen-antibody or enzyme-substrate, to separate compounds.

Centrifugation is a technique used for the separation of particles from a solution according to their size, shape, density, viscosity of the medium and rotor speed. The particles are suspended in a liquid medium and placed in a centrifuge tube. The tube is then placed in a rotor and spun at a define speed. The denser particles settle at the bottom while the less dense particles remain at the top. It is used in hospitals for blood and urine test. it is also used to separate blood cells from plasma in the blood.

A separating funnel can be used to separate a mixture of two immiscible liquids with different densities. Here, the liquids make a distinct layer and with the denser particles settling at the bottom. The corresponding layers can be seperated by using a seperating funnel which separats out the top lense layer and leaves the denser layer. A mixture of petrol and oil can be separated using a separating funnel.

This method is used to separate a solid from a mixture of two miscible liquids. It takes advantage of the principle of difference in solubilities of solids in miscible liquids. For example, Iron (III) chloride (FeCl₃) and sodium hydroxide (NaOH) react to form sodium chloride (NaCl) and insoluble iron (III) hydroxide (Fe(OH)₃).

A pure substance is a substance that contains no impurity. Pure substances have a definite boiling and melting point. An impure substance has no definite or fixed boiling and melting point due to the presence of impurities. Note: Impurities lower melting point of solids and raises the boiling point of liquids.

• Pure substances have a fixed melting and boiling points. For example, Ethanol boils at 78°C.
• Pure substances are homogeneous in nature
• Pure substances have a definite density
• Coloured pure substances give a spot on a paper chromatogram

We can test for the purity of a substance by determining its melting and boiling point.

1. Determination of boiling point of liquid (Ethanol)
Boil a small sample of ethanol in a boiling tube and heat in a water bath. insert a laboratory thermometer into the sample of ethanol to detect its temperature. Heat the liquid until ethanol begins to boil measure the temperature. If ethanol is pure it will begin to boil at exactly 78°C.
2. Determination of melting point of a solid using Naphthalene
Heat a sample of Naphthalene in a water bath and determine the temperature at which it turns into liquid. Pure Naphthalene melts at 80°C