Study how chromatography, distillation and other physical methods separate mixtures. Understand the principles behind each technique and how to select a suitable method for a given mixture.
Chromatography separates components of a mixture because they travel at different rates through a stationary medium under the influence of a mobile phase. It is used to separate dyes and plant pigments, purify compounds and check the purity of a sample.
Answer: Chromatography is a separation technique in which mixture components move at different rates through a stationary medium. The stationary phase stays in place, while the mobile phase moves and carries the components.
Answer: The Russian botanist Mikhail Tswett developed chromatography in 1906 while separating plant pigments.
Answer: The stationary phase is the material that remains fixed, such as paper or silica. The mobile phase is the moving solvent or fluid that carries the sample through or over the stationary phase.
Answer: Different dyes have different solubilities in the solvent and different attractions to the paper. As a result, they travel different distances and form separate spots.
Answer: Pencil graphite is largely insoluble in the solvent and usually does not travel with the solvent. Ink may dissolve and create extra spots, interfering with the results.
Answer: It can separate pigments in plant extracts and help identify substances in forensic, medical or chemical samples.
Answer: A mixture is placed on a column containing a stationary material such as silica or alumina. A solvent passes through the column. Components interact differently with the stationary and mobile phases, so they travel at different rates and can be collected separately.
Distillation separates substances by using differences in volatility or boiling point. A liquid is heated to form vapour, and the vapour is cooled in a condenser to obtain liquid again. The appropriate method depends on the substances and how close their boiling points are.
Answer: Distillation uses differences in volatility or boiling points. The more volatile component enters the vapour phase more readily; cooling that vapour produces a separated liquid.
Answer: Cold water removes heat from the vapour, allowing it to condense into liquid that can be collected in a receiver.
Answer: Fractional distillation separates miscible liquids with relatively close boiling points by using a fractionating column. Repeated vaporisation and condensation enrich the vapour in the more volatile component.
Answer: Simple distillation is useful when the boiling points differ sufficiently or when separating a volatile liquid from non-volatile dissolved solids. Fractional distillation uses a fractionating column and is better for separating miscible liquids with close boiling points.
Answer: Fractional distillation is generally more suitable because the boiling points are close. The fractionating column allows repeated condensation and vaporisation, improving separation.
Answer: By distillation. Water is vaporised from the seawater and then condensed in a separate receiver, while most dissolved salts remain in the original vessel. The apparatus should be used safely under appropriate supervision.
Answer: Evaporation removes the solvent and leaves the dissolved solid behind. Crystallisation is often preferred when a purer solid is required because crystals can form as a solution cools and impurities may remain in the solution.
Answer: Slow formation of crystals can give a purer solid and avoids overheating a substance that may decompose. Some impurities remain in the remaining solution instead of entering the crystal structure.
Answer: Magnetic separation. Iron is attracted by a magnet, whereas sulphur is not, so the two components can be separated by exploiting their different magnetic properties.
Answer: First use a magnet to remove the iron filings. Add water to the remaining sand and salt so that the salt dissolves. Filter the mixture to collect sand as the residue. Finally, evaporate the filtrate or crystallise it to recover the salt.
Answer: Sublimation is the direct change of a solid into vapour without passing through the liquid state. It can be used to separate a sublimable substance, such as ammonium chloride, from a non-sublimable solid under suitable laboratory conditions.
Answer: Centrifugation spins a mixture rapidly so that components separate according to differences in their effective settling behaviour or density. It is used, for example, to separate cream from milk or to separate suspended particles from a liquid.
Answer: Filtration separates an insoluble solid from a fluid by passing the mixture through a porous filter. The solid is retained as residue and the fluid passes through as filtrate. It cannot separate dissolved salt from salt solution because dissolved particles pass through ordinary filter paper.
Answer: Black ink contains more than one coloured component. The components travel at different rates because their interactions with the paper and solvent differ.
Answer: Sand is insoluble and its particles are retained by the filter. Salt dissolves into very small ions that pass through the pores of ordinary filter paper along with the water.
Answer: Simple distillation may be appropriate because the boiling points differ substantially. The more volatile component tends to vaporise first, and its vapour can be condensed and collected. The exact procedure depends on the mixture and apparatus.
Answer: Both statements are correct, and the reason explains how chromatography can reveal multiple components in a sample.
Answer: Both statements are correct, and the reason explains why fractional distillation improves separation.
Answer: Chromatography is suitable because the pigments differ in their solubility and attraction to the stationary phase, so they travel at different rates.