Separation Techniques - Class VII

Pure solids can be obtained from its impure sample by crystallisation.
Crystallisation is used to purify solids.

Some solids decompose or some, like sugar, may get charred on heating to dryness. Some impurities may remain dissolved in the solution even after filtration. On evaporation these contaminate the solid. So, crystallisation is better than evaporation.

Different substances form crystals of different shapes and colours.

When a mixture of common salt and ammonium chloride is heated, white fumes are liberated which changes into a white deposit when cooked. This white substance is ammonium chloride. Salt and Ammonium chloride are separated by the method of sublimation.

Substances like camphor, ammonium chloride, naphthalene, benzoic acid, iodine sublime on heating.
$\underset{(Impure)}{Solid}    \xrightarrow{\Delta}     vapour     \xrightarrow{cool}    \underset{Sublimate}{solid(pure)}$

A mixture of barium sulphate and $H _2O$ can be separated by the method of filtration. Barium sulphate is insoluble in water.  During filtration, barium sulphate remains on the filter paper and water passes as through filter paper as filtrate.

The purity of the solid salt sample can be anaylsed simply by checking its solubility in proper solvent,

Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase. Sublimation is easier for volatile materials which can be evaporated at low temperatures.

Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase.

Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase. 

Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase. Ammonium chloride, camphor, anthracene, napthalene can sublime but common salt cannot sublime. Hence, option D is correct.

There are many substances which are converted into gas from solid when heated, and converted from gas to solid when cooled without converting into liquid. Such substances are known as sublime and the proce3wss is called sublimation.

Ammonium chloride changes directly from solid to gaseous state on heating. Hence, on heating ammonium chloride, it gets converted into white vapours. The gaseous form of ammonium chloride can be cooled easily to get a pure solid.

Ammonium chloride changes directly from solid to gaseous state on heating. The gaseous form of ammonium chloride can be cooled easily to get a pure solid. Hence, it acts as a sublimate.

Evaporation technique is used to separate salt from the filtrate. Common salt does not decompose during evaporation. As the water evaporates, fewer and fewer water molecules are present to keep the salt particles apart. The salt therefore recrystallizes and can be collected.

Both salt and ammonium chloride are white in colour and soluble in water. They can't be separated by any other method except sublimation.

During separation procedure of ammonium chloride from salt by evaporation an inverted funnel is used which is plugged with cotton boll, so that ammonium chloride do not evaporate.

The component which is less soluble will get precipitated out and settle at the bottom and other component which is more soluble will remain in the solution

The ammonium chloride molecule in separation from salt sublime and get separated. This is a sublimation process which is used to separate two solids. Here salt being non-volatile does not undergo sublimation. 

In Electrolysis, the current is passed through the solution and compound gets ionised, with electrolysis we can separate hydrogen and oxygen from pure water, but we can't use this method to separate components of a mixture.

Sublimation is the procedure in which solids on heating directly converts into vapor without converting into liquid phase. 

In fractional crystallization, the component with low solubility will crysatllize first and one with high solubility will crystallize latter, so substances can be refined based on the difference on their solubility.

Salt (NaCl) is a non-volatile substance which do not evaporate on heating directly. Ammonium chloride is a volatile substance which can evaporate on heating.

The mixture of sugar and chalk powder can be separated by addition of water. Sugar will dissolve in water while chalk will not. The mixture can be filtered and separated.

Physical separation techniques depend on the physical properties of the substance. These physical properties include physical state, solubility, boiling point, melting point, density, specific gravity, electrical and magnetic properties.

1. Washing: Insoluble solids like noble metals and compounds like silica can be washed with water until all the other impurities leave them. Washing can also be done with organic solvents when there is a mixture with soluble impurities and insoluble compound.
2. Decanting: When the densities of two liquids that are immiscible in one another are to be separated this method can be used. Separating funnel helps to separately collect the tow liquids. In case of solids the lighter solids can be separated by decanting it in water medium when both of the solids are not soluble. By blowing air also the separation can be done with very light and heavy solid mixtures.
3. Distillation: Mixtures of liquids can be separated when their boiling points are different by this technique. The mixture is slowly heated in a distillation flask. The component having the low boiling point vaporizes first. The vapors are collected by condensing them in Leibig's condenser. Mixtures containing more than two liquids can also be separated by this technique but the difference in boiling points must be at least 20C between each of them. Distillation can also be used to separate dissolved salts from their aqueous solutions. Sea water is distilled by the Sun rays to form clouds which rain fresh water without salts. Mixture of gases are separated by reducing their temperature and converting all the gases in to liquid state. By gradational increasing of temperatures each liquified gas gets converted into gaseous state and can be separated.
4. Fractional distillation: When the difference in the boiling points are nearby to each other and not much, a detailed distillation is carried out which is called fractional distillation. It is done in a column called fractionating column. Fractionating column allows the condensation of different solvents at different temperatures and sending back the mixture fraction in to the flask. Petroleum distillation is done in the fractionating column in to various components over a wide range of temperatures. Melting point differences can also be utilized in the same way as boiling point in separation of mixtures. Icebergs are formed which are solidified fresh water is based on the depression of freezing point phenomenon.
5. Solubility: Different compounds have different amounts of solubility at a certain temperature. When no more solid is soluble in solvent at a particular temperature it is called its saturation point at that temperature. In a mixture if one component is more soluble and the other less at a given temperature, they can be separated by this technique.
6. Electrical and Magnetic separation: Electrolytes and non electrolytes, magnetic and non magnetic substances can be separated by this technique of separation using either electrical field or magnetic field.

sugar is organic,(contains carbon) and is soluable in organic solvents like alcohol. Salt is insoluable in alcohol. 
Add alcohol to the mixture, filter out the salt, then evaporate the alcohol and the sugar will be left.

Ammonium chloride on heating changes into white vapors and then solidifies on cooling.

Both common salt and ammonium chloride are white powdery substance and dissolve in water to  form a homogeneous mixture. On filtration, none of these will separate form the liquid.  A mixture of common salt and ammonium chloride can be separated by sublimation.

Sublimation is conversion of solid of vapors on heating and vapors to solid on cooling. The solid which undergoes sublimation is called sublime, whereas the solid obtained by cooling vapors is called sublimate.

Sublimation can be used to separate all those substances which can sublimise easily like naphthalene, ammonium chloride and anthracene.

Ammonium chloride changes directly from solid to gaseous state on heating. Hence, it can be separated from sand using sublimation.

Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase. Ammonium chloride, camphor, anthracene can sublime but common salt cannot sublime.

There are many substances which are converted into gas from solid when heated, and converted from gas to solid when cooled without converting into liquid. Such substances are known as sublime. For example, ammonium chloride, naphthalene balls, camphor, etc.

Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase. Ammonium chloride, camphor, anthracene, napthalene can sublime but common salt cannot sublime. Ammonium chloride evaportaes and forms vapours which rise up the funnel and get deposited in the cooler parts of the funnel. Sodium chloride remains in the china dish as no reaction takes place.

If the dish in not plugged properly during sublimation, the vapors will escape and cannot be converted into solid on cooling. Thus, separation becomes difficult.

Evaporation technique is used to separate salt from the filtrate. Common salt does not decompose during evaporation. As the water evaporates, fewer and fewer water molecules are present to keep the salt particles apart. The salt, therefore, recrystallizes and can be collected. 

Ammonium chloride doesn't actually undergo sublimation upon heating. It decomposes and forms ammonia gas and hydrogen chloride gas.Thus the given statement is true.

Sublimation is the process of transition of a substance from the solid to the gaseous state without passing through the liquid state. Non-volatile compounds cannot vaporise and hence, cannot undergo sublimation.

In crystallisation, the impure substance is dissolved in a suitable solvent to reach its nearly saturated solution at a temperature higher than the room temperature. At this high temperature, the solute has very high solubility in that solvent, so a much smaller quantity of hot solvent is needed for dissolving the solute than the solvent at room temperature.  When the solution is cooled, the pure substance is crystallised. The solution left behind is called mother liquor. All the impurities are left behind in the mother liquor. The purification method depends on the differences in solubility between the compound and the impurity.     

Fractional crystallization is the method of refining substances based on the differences in their solubility. If a mixture of two or more substances in a solution is allowed to crystallise, the least soluble substance will crystallise first. The proportion of the components in the precipitate will depend on their solubility product.

A separating funnel is used to separate the components of a mixture of cooking oil and water. A separating funnel is used to separate the components of a mixture of two immiscible liquids. Cooking oil and water are two immiscible liquids.

A public health inspector suspects that in addition to two harmless
dyes(boiling points 69 C and 71 C), a lollipop also contains a poisonous
green dye (boiling point 73 C). Paper chromatography can be used to confirm his suspicion. Here, different dyes will have different affinity for paper (stationary phase) and solvent (mobile phase). Fractional distillation is used when individual components of mixtures have boiling points more than 30 C. Filtration and crystallisation are used in separation / purification of solid from liquid.

To separate the mixture of salt and sand;