Classification of Matter Can Be Summarized As Follows

Describe appropriate ways to separate the components of different types of mixtures (sorting, evaporation, filtration, magnets, boiling, chromatography, screening.

Describe how paper chromatography is used to separate the mixtures of ink in a black sharpie pen.

Some of the methods for separation of mixtures are: Sedimentation or Decantation, Filtration, Evaporation, Chromatography , Crystallization, Sublimation, Magnetic, and Gravity method.

Classification of matter can be summarized as follows:

Because molecules in ink and other mixtures have different characteristics (such as size and solubility), they travel/migrate at different speeds (distance/time) when pulled along a piece of paper by a solvent (in this case, alcohol). For example, black ink contains several colors. When the water flows through the ink, the molecules of each one of the colors behave differently, resulting in a sort of “rainbow” effect. Chromatography is used to separate mixtures of substances into their components.

All forms of chromatography work on the same principle.

1 They all have a stationary phase (a solid, or a liquid supported on a solid: This is the Chromatography paper) and a mobile phase (a liquid or a gas: This is the alcohol). The mobile phase (alcohol) flows through the stationary phase (chromatography paper) and the mobile phase carries the components of the mixture (the ink) with it. Different components or colors of the ink travel at different rates. Look at the different colors and where they are on the paper.

A mixture is a combination of two or more elements or compounds in any proportion so that the components do not lose their identity. Air is an example of a mixture (several gases mix to form air).

Mixtures are of two types, homogeneous and heterogeneous.

Homogeneous mixtures have the same composition throughout the sample. The components of such mixtures cannot be seen under a powerful microscope. They are also called solutions. Examples of homogeneous mixtures are air, sea-water, gasoline, brass etc.

Heterogeneous mixtures consist of two or more parts (phases), which have different compositions. These mixtures have visible boundaries of separation between the different constituents and can be seen with the naked eye e.g., sand and salt, chalk powder in water etc.

Separation of Mixtures

The separation of mixtures into its constituents in a pure state is an important process in chemistry. The constituents of any mixture can be separated on the basis of their differences in their physical and chemical properties e.g., particle size, solubility, effect of heat, acidity or basicity etc.

Mixtures

A mixture is a combination of two or more elements or compounds in any proportion so that the components do not lose their identity. Air is an example of a mixture (several gases mix to form air). Mixtures are of two types, homogeneous and heterogeneous. Homogeneous mixtures have the same composition throughout the sample. The components of such mixtures cannot be seen under a powerful microscope. They are also called solutions. Examples of homogeneous mixtures are air, sea-water, gasoline, brass etc. Heterogeneous mixtures consist of two or more parts (phases), which have different compositions. These mixtures have visible boundaries of separation between the different constituents and can be seen with the naked eye e.g.sand and salt, chalk powder in water etc.

Separation of Mixtures

Some of the methods for separation of mixtures are Sedimentation or Decantation

AimTo separate the mixture of coarse particles of a solid from a liquid e.g., muddy river water.

2 Sedimentation or Decantation Aim To separate the mixture of coarse particles of a solid from a liquid e.g., muddy river water. Experiment Aim To separate the mixture of coarse particles of a solid from a liquid e.g., muddy river water. Principle The coarse particles of the solid being heavier than the liquid (usually water), settle down due to gravity. The clear upper layer of the liquid is then gently poured out into another container. Settling down of the coarse particles due to the effect of gravity is called sedimentation. The mechanical transfer of the clear upper liquid without disturbing the settled solid particles is called decantation. Process The mixture is taken in a container and allowed to stand for sometime. The solid particles settle down with time. Settling down of the particles leaves the upper layers of the liquid clearer. Bigger particles settle down faster than the finer particles. Sometimes the sedimentation process is hastened by adding a small quantity of alum. Al3+ ions in alum cause the coagulation of the fine particles by undergoing hydrolysis to Al(OH)3 that has a strong tendency for adsorption.

3 Fig: 1.1 - Separation of the coarse particles of a solid from a liquid by sedimentation and decantation Filtration Aim To separate the insoluble solid component of a mixture from the liquid completely i.e. separating the precipitate (solid phase) from any solution. Experiment Aim To separate the insoluble solid component of a mixture from the liquid completely i.e. separating the precipitate (solid phase) from any solution. Principle The solvent molecules and the molecules/ions present in the solution can pass through the porous membranes while the suspended particles cannot and are retained on the porous membrane. Process The solution containing the suspended impurities is made to pass through the porous membrane such as filter paper, filter cloth etc. The solvent or solution containing dissolved substances passes through the porous membrane, which is called filtrate. The insoluble solid suspended particles that remain on the porous membrane is termed residue. When the suspended impurities are very fine, a small amount of alum added to the suspension makes filtration faster.

4 Fig:1.2 - Separation by filtration

Evaporation Aim To separate a non-volatile soluble salt from a liquid or recover the soluble solid solute from the solution. The solvent is lost into the surroundings. Experiment Aim To separate a non-volatile soluble salt from a liquid or recover the soluble solid solute from the solution. The solvent is lost into the surroundings. Principle Liquids evaporate at all temperatures. Evaporation becomes faster at higher temperatures. Process The solution containing the mixture is taken in a china dish and heated gently. Gradually the solvent evaporates and the solution containing the dissolved solute becomes thicker. The semi-solid mass left on the china dish is slowly heated to dryness.

5 Fig: 1.3 - Evaporation of a solution

Crystallization This method is used to separate a solid compound in pure and geometrical form. A nearly saturated solution of an impure substance is prepared in a hot solvent. The prepared solution is quickly filtered and the filtrate is then allowed to cool slowly in a china dish. The resulting pure crystals that form are removed with the help of a spatula. They are dried by pressing them between the folds of filter papers and finally put into a dessicator.

Sublimation This method is used to separate volatile solids, from a non-volatile solid. The mixture is taken in a china dish covered with a perforated filter paper on which an inverted glass funnel is placed to collect the vapours. Upon heating, the substance vapourizes and gets deposited on the walls of the funnel. The non-volatile substances are left in the dish. Distillation Distillation is used for separating the constituents of a liquid mixture, which differ in their boiling points. Depending upon the difference in the boiling points of the constituents, different types of distillation like fractional distillation, steam distillation etc. are employed.

6 Magnetic Separation Method Aim To separate a magnetic component from a mixture containing non- magnetic components. Experiment Aim To separate a magnetic component from a mixture containing non-magnetic components. Principle The magnetic component of the mixture is separated with the help of the magnetic attraction. Process A magnet is moved over the mixture containing the magnetic substance e.g., iron filings. These get attracted to the magnet. The process is repeated until the magnetic material is completely separated from the mixture.

Fig: 1.4 - Separation of a magnetic substance by a magnet

Gravity method

7 Aim To separate mixtures in which components have different densities. Principle Particles with higher density settle to the bottom while the lighter particles are separated through various processes such as winnowing (grain separation) and washing (panning of gold in the river bed). Process Riverbed sand containing fine particles of gold is repeatedly washed in a pan with flowing water. Gold particles settle to the bottom of the pan because of higher density while lighter sand particles are washed over the edge of the pan. Solvent Extraction Method Organic compounds, which are easily soluble in organic solvents but insoluble or immiscible with water forming two separate layers can be easily separated. The aqueous solution of the mixture is mixed with a small quantity of organic solvent in a separating funnel. The separating funnel is stoppered and shaken strongly. It is allowed to stand for some time. The organic liquid and water form separate layers, which are collected by opening the stop-cock. The aqueous layer is again transferred to the separating funnel. The process is repeated with more organic solvent.