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Q1. Chromatography was first used to separate
Chromatography was first used to separate colours from natural sources. The word itself comes from Greek words meaning “colour” and “writing,” as it was originally used to separate pigments in plants and other coloured substances. Today, chromatography is used to separate many different types of mixtures, but its earliest application was for separating colours.
Q2. Fractional distillation is used to separate
Fractional distillation is used to separate gases from air. Air is a mixture of gases like nitrogen, oxygen, and argon, which have different boiling points. By cooling air to very low temperatures and then gradually warming it, the gases can be separated one by one based on their boiling points. This is the industrial method used to obtain pure gases from air.
Q3. The crystals obtained in crystallisation are generally
The crystals obtained in crystallisation are generally alike in shape. Each substance has a characteristic crystal shape or habit. For example, copper sulphate forms blue rhombic crystals, while salt forms cubic crystals. When a substance is purified by crystallisation, all the crystals have the same shape because they have the same internal arrangement of particles.
Q4. Oxygen is obtained from air by
Oxygen is obtained from air by fractional distillation. Air is first compressed and cooled to become liquid air. Then, it is warmed slowly in a fractionating column. Since different gases have different boiling points, they vaporise at different temperatures. Nitrogen (boiling point -196°C) vaporises first, followed by argon, and then oxygen (boiling point -183°C). This is how oxygen is separated from air.
Q5. A separating funnel is used to separate
A separating funnel is used to separate two immiscible liquids. Immiscible liquids are those that do not mix with each other and form separate layers, such as oil and water. The separating funnel allows the denser liquid to be drained out from the bottom while the lighter liquid remains on top. This method is based on the difference in density between the two liquids.
Q6. The word chromatography comes from the Greek word meaning
The word chromatography comes from the Greek words “chroma” meaning colour and “graphein” meaning to write. It was originally used to separate coloured substances, and the name was given because the technique separated colours on paper. Today, chromatography is used to separate both coloured and colourless substances, but the name reflects its historical origin.
Q7. Washing machines use centrifugation to
Washing machines use centrifugation to squeeze out water from wet clothes. During the spin cycle, the clothes are spun rapidly in a drum with holes. The centrifugal force pushes the water outwards through the holes, separating it from the clothes. This physical method removes excess water, making the clothes drier, but it does not dry them completely.
Q8. Centrifugation is used in dairies to separate
Centrifugation is used in dairies to separate butter from cream. When cream is churned, butter separates from butter milk. In large-scale dairy production, centrifugation is used to separate cream from milk, and then to separate butter from cream. This method uses the difference in density between the components.
Q9. Kerosene oil and water can be separated using
Kerosene oil and water can be separated using a separating funnel. These two liquids are immiscible (do not mix) and form two separate layers with water at the bottom (denser) and kerosene at the top (lighter). The separating funnel allows the denser water to be drained out first, leaving the kerosene behind.
Q10. Chromatography is used to separate
Chromatography is used to separate drugs from blood in forensic and medical testing. It is a powerful technique that can separate small amounts of substances from complex mixtures like blood samples. While it is also used to separate pigments and dyes, the separation of drugs from blood is a practical application of chromatography in medicine and forensics.
Q11. Ink is a mixture of
Ink is a mixture of dye (or pigment) and water (or sometimes alcohol). The dye provides the colour, and the water acts as the solvent. In chromatography, ink is often used as an example because the different dyes in the ink can be separated based on their different solubilities in the solvent.
Q12. In distillation, vapours are converted back to liquid by
In distillation, the vapours are converted back to liquid by condensation. When the vapours rise and reach the condenser, they are cooled by passing cold water around the condenser tube. The vapours lose heat and change back into liquid form, which is collected as the distillate. This is the reverse of evaporation.
Q13. Which method uses difference in boiling points?
Distillation uses the difference in boiling points of the components in a mixture. When a mixture is heated, the component with the lower boiling point vaporises first, and the vapours are then condensed and collected. This method is used to separate liquids that have different boiling points, such as acetone and water or alcohol and water.
Q14. Impurities are removed before crystallisation by
Impurities are removed before crystallisation by filtration. The hot saturated solution is filtered to remove any insoluble impurities and dust particles. This ensures that the crystals that form are pure. Filtration is an important preparatory step in the crystallisation process.
Q15. Water remains in the distillation flask because
Water remains in the distillation flask because it has a higher boiling point (100°C) compared to many other liquids. In a mixture like alcohol-water, alcohol has a lower boiling point and vaporises first, leaving water behind in the flask. This is how distillation separates liquids based on their boiling points.
Q16. Air is first converted into liquid air by
Air is first converted into liquid air by compression and cooling. Air is compressed to increase its pressure, and then it is cooled to very low temperatures. Under high pressure and low temperature, air becomes a liquid. This liquid air is then used in fractional distillation to separate its components based on their boiling points.
Q17. In chromatography, water acts as a
In chromatography, water acts as a solvent. It dissolves the dyes in the ink and carries them up the chromatography paper by capillary action. The solvent (water) moves through the paper, and the different dyes are carried along at different rates based on their solubility and adsorption.
Q18. Centrifugation is used in diagnostic laboratories for
Centrifugation is used in diagnostic laboratories for blood and urine tests. In blood tests, centrifugation separates plasma from blood cells, allowing doctors to analyse the components separately. In urine tests, centrifugation helps separate solid particles from urine for microscopic examination. This is a common and important application in medical diagnostics.
Q19. Copper sulphate crystals are obtained by
Copper sulphate crystals are obtained by crystallisation. A saturated solution of copper sulphate is prepared, and then it is allowed to cool slowly. As the solution cools, the solubility decreases, and pure copper sulphate crystals form. Crystallisation gives crystals with a characteristic blue colour and rhombic shape.
Q20. Chromatography is used to separate solutes that
Chromatography is used to separate solutes that dissolve in the same solvent. In chromatography, different solutes are separated based on their different solubilities in the solvent and their different affinities for the stationary phase (paper). If the solutes did not dissolve in the solvent, they would not move and could not be separated.
Q21. Crystallisation separates solid from
Crystallisation separates a solid from a solution. The solid is dissolved in a solvent to form a solution, and then the solution is allowed to evaporate or cool so that the solid comes out in the form of pure crystals. This method is used to purify solids and is widely used in industries and laboratories.
Q22. In chromatography, the dye that is more soluble
In chromatography, the dye that is more soluble in the solvent moves faster up the paper. The more soluble a dye is, the more it dissolves in the solvent and the faster it travels along with the solvent front. The less soluble dyes move slower and stay closer to the starting point. This difference in solubility is what allows chromatography to separate different dyes.
Q23. Distillation is used to separate
Distillation is used to separate two miscible liquids with different boiling points. Miscible liquids mix completely, like alcohol and water. They can be separated by distillation because they have different boiling points. The liquid with the lower boiling point vaporises first and is collected separately from the one with the higher boiling point.
Q24. Slag is removed because it is
Slag is removed because it is lighter than the molten metal and floats on top. In the extraction of metals, slag is the waste material that separates from the molten metal. Because it is less dense, it forms a layer on top and can be easily removed. The principle is similar to using a separating funnel.
Q25. Separation of mixtures makes it possible to
Separation of mixtures makes it possible to study the individual components. By separating a mixture, we can analyse the properties, composition, and behaviour of each component in detail. This is essential for understanding what a substance is made of, and for obtaining pure substances for use in various applications.
Q26. Sublimation is used to separate mixtures containing
Sublimation is used to separate mixtures containing a sublimable solid and a non-sublimable solid. For example, a mixture of camphor (sublimable) and salt (non-sublimable) can be separated by sublimation. The camphor changes directly from solid to gas when heated, leaving the salt behind. The camphor vapour can then be collected and condensed back to solid.
Q27. In distillation, the liquid that vaporises first has
In distillation, the liquid that vaporises first has a lower boiling point. When a mixture of two or more liquids is heated, the component with the lowest boiling point boils first and turns into vapour. This vapour is then condensed and collected as the distillate. The liquids are separated based on this difference in boiling points.
Q28. The rise of coloured spots on paper is due to
The rise of coloured spots on paper in chromatography is due to their solubility in the solvent. The solvent moves up the paper by capillary action, and the coloured substances dissolve in it. The dissolved substances are carried upwards at different rates depending on their solubility and affinity for the paper. This separates the components.
Q29. In a separating funnel, the lower layer is usually
In a separating funnel, the lower layer is usually water because it is denser than most organic liquids like oil or kerosene. When two immiscible liquids are placed in a separating funnel, the denser liquid settles at the bottom and the less dense liquid floats on top. Water is denser than oil, so water is typically the lower layer.
Q30. Fractional distillation is used when boiling point difference is
Fractional distillation is used when the boiling point difference between the components is less than 25 K. When the boiling points are very close (less than 25 K apart), simple distillation cannot separate them effectively. A fractionating column is used to provide more surface area for condensation and re-evaporation, allowing better separation of components with close boiling points.
Q31. Air is separated into its components by
Air is separated into its components by fractional distillation. Air is first cooled and compressed to liquid form, and then the liquid air is slowly warmed in a fractionating column. The different gases boil at different temperatures and are collected separately. This is how nitrogen, oxygen, and other gases are obtained from air.
Q32. Which of the following substances sublimes?
Ammonium chloride sublimes. When heated, it changes directly from solid to gas without passing through the liquid state. The white solid disappears and reappears as a solid on cooler surfaces. Sugar, copper sulphate, and common salt do not sublime; they melt when heated.
Q33. Which method uses density difference and spinning?
Centrifugation uses density difference and spinning. When a mixture is spun rapidly, the denser particles move to the bottom due to centrifugal force. This separates components based on their density. It is commonly used to separate cream from milk, sediment from liquids, and in diagnostic tests.
Q34. In crystallisation, solution is allowed to
In crystallisation, the solution is allowed to cool slowly. Slow cooling allows the solute particles to arrange themselves in an orderly manner, forming well-shaped pure crystals. If the solution is cooled rapidly, many small crystals may form, and impurities may get trapped. Slow cooling is essential for obtaining good quality crystals.
Q35. Anthracene is an example of a
Anthracene is an example of a sublimable solid. Like camphor and naphthalene, anthracene changes directly from solid to gas when heated without melting. This property allows it to be purified by sublimation, separating it from non-sublimable impurities.
Q36. Crystallisation separates a solid in the form of
Crystallisation separates a solid in the form of crystals. The solid comes out of the solution as well-defined, regular-shaped crystals. Each substance has a characteristic crystal shape. Crystallisation gives pure solids in the crystalline form, which is why it is used for purification.
Q37. Naphthalene can be separated from impurities by
Naphthalene can be separated from impurities by sublimation. Naphthalene is a sublimable solid (used in mothballs). When the mixture is heated, naphthalene changes directly from solid to gas, leaving the non-sublimable impurities behind. The naphthalene vapour can then be cooled to get pure naphthalene crystals.
Q38. Separating techniques are used because most substances are
Separating techniques are used because most substances in nature are mixtures. Natural substances like air, water, soil, and minerals are mixtures of different components. We need to separate these components to obtain pure substances for various uses. Separation techniques help us isolate and study individual components.
Q39. Camphor changes directly from solid to
Camphor changes directly from solid to gas when heated. This process is called sublimation. Camphor does not melt into a liquid; it sublimes, meaning it changes from the solid state directly to the gaseous state. This property is used to separate camphor from impurities.
Q40. Fractionating column is filled with
A fractionating column is filled with glass beads. The glass beads provide a large surface area for the vapours to condense and re-evaporate multiple times. This increases the efficiency of separation when the boiling points of the components are very close. The repeated condensation and evaporation helps in achieving better separation.
Q41. Acetone and water are separated by
Acetone and water are separated by distillation. Acetone has a lower boiling point (56°C) compared to water (100°C). When a mixture of acetone and water is heated, acetone vaporises first and can be collected by condensation. This separates the two miscible liquids based on their different boiling points.
Q42. Glass beads in fractionating column provide
Glass beads in a fractionating column provide a surface for condensation. The vapours condense on the glass beads and then re-evaporate. This repeated cycle allows better separation of liquids with close boiling points by providing more surface area and allowing equilibrium to be established at each theoretical plate.
Q43. Oil and water form separate layers because they
Oil and water form separate layers because they are immiscible. Immiscible liquids do not mix with each other and form two distinct layers. Oil is less dense than water, so it floats on top, and water stays at the bottom. This property allows them to be separated using a separating funnel.
Q44. The principle of separating funnel is based on difference in
The principle of a separating funnel is based on the difference in density of the two immiscible liquids. The denser liquid settles at the bottom and is drained out first, while the lighter liquid remains on top. This density difference allows the liquids to be separated easily.
Q45. The gas with lowest boiling point liquefies
The gas with the lowest boiling point liquefies first when a mixture of gases is cooled. In fractional distillation of air, nitrogen (boiling point -196°C) is the first to liquefy, followed by argon and then oxygen (-183°C). This is because the gas with the lowest boiling point condenses at a higher temperature compared to gases with lower boiling points.
Q46. Crystallisation is used to obtain
Crystallisation is used to obtain pure solids. When a solid is dissolved in a solvent and then allowed to crystallise, the crystals that form are pure. Impurities remain in the solution. This is why crystallisation is an important method of purification for solids in chemistry.
Q47. In extraction of iron, separating funnel principle is used to remove
In the extraction of iron, the separating funnel principle is used to remove slag. Slag is the waste material formed during the smelting process. It is less dense than molten iron, so it floats on top and can be removed. This is similar to how a separating funnel separates two immiscible liquids based on density difference.
Q48. Chromatography is used to separate
Chromatography is used to separate the components of a dye. A dye is often a mixture of different coloured compounds. Chromatography separates these components based on their different solubilities in a solvent. This technique is widely used in the analysis of inks, food colours, and pigments.
Q49. Gases separate in fractional distillation according to their
Gases separate in fractional distillation according to their boiling points. When liquid air is warmed, the gas with the lowest boiling point vaporises first and is collected. As the temperature continues to rise, gases with progressively higher boiling points vaporise. This allows the components of air to be separated.
Q50. Crystallisation is better than evaporation because it
Crystallisation is better than evaporation because it gives pure crystals. In evaporation, the solution is heated until all the solvent evaporates, leaving behind the solid along with any impurities that were present. In crystallisation, the solid is allowed to form slowly as crystals, which exclude impurities and result in a much purer product.