Question: 22. What are the favourable qualities given to gold when it is alloyed with copper or silver for the purpose of making ornaments? ed with copper or silver for making of ornaments.
Answer: Since, Gold is a highly malleable metal so it is difficult to make the ornaments with pure gold, thus to make its rigidity desiring gold is alloyed with copper or silver for making of ornaments.
Question: 23. An element is sonorous and highly ductile. Under which category would you classify this element? What other characteristics do you expect the element to possess?
Answer: Since a metal is sonorous and ductile, thus if an element possesses these qualities this will be kept under the category of metals. The other qualities of metal are good conductor of heat and electricity, lustrous, malleability, etc.
Question: 24. Give an example each for the mixture having the following characteristics. Suggest a suitable method to separate the components of these mixtures
(a) A volatile and a non-volatile component.
Answer: The mixture of acetone and water. In this acetone is volatile and water is non-volatile. The mixture of water and acetone can be separated by the process of distillation.
(b) Two volatile components with appreciable difference in boiling points.
Answer: Mixture of acetone and ethanol. The boiling point of acetone is 560C and that of ethyl alcohol is 78.40C.
The mixture of acetone and ethanol can Answer: Mixture of acetone and ethanol. The boiling point of acetone is 560C and that of ethyl alcohol is 78.40C.
The mixture of acetone and ethanol can be separated using fractional distillation. er are two immiscible liquids, thus their mixture can be separated using separating funnel.
(d) One of the components changes directly from solid to gaseous state.
Answer: The mixture of salt and ammonium chloride. In this mixture ammonium chloride changes from solid to gaseous state directly.
The mixture of salt and ammonium chloride can be separated by the process of sublimation.
(e) Two or more coloured constituents soluble in some solvent.
Answer: The ink is the mixture of dyes of many colours. The different dyes of ink can be separated using chromatography.
Question: 25. Fill in the blanks
(a) A colloid is a __________ mixture and its components can be separated by the technique known as _________.
Answer: heterogeneous, centrifugation
(b) Ice, water and water vapour look different and display different _________ properties but they are ___________ the same.
Answer: Physical, chemically
(c) A mixture of chloroform and water taken in a separating funnel is mixed and left undisturbed for some time. The upper layer in the separating funnel will be of________ and the lower layer will be that of ___________.
Answer: chloroform, water
(d) A mixture of two or more miscible liquids, for which the difference in the boiling points is less than 25 K can be separated by the process called____________.
Answer: Fractional distillation
(e) When light is passed through water containing a few drops of milk, it shows a bluish tinge. This is due to the _________ of light by milk and the phenomenon is called _________ . This indicates that milk is a ________ solution.
Answer: scattering, Tyndall Effect, colloidal
Question: 26. Sucrose (sugar) crystals obtained from sugarcane and beetroot are mixed together. Will it be a pure substance or a mixture? Give reasons for the same.
Answer: Pure substance, since it contains a single component, i.e. sucrose.
Question: 27. Give some examples of Tyndall effect observed in your surroundings?
Answer: Examples of Tyndall Effect:
Question: 28. Can we separate alcohol dissolved in water by using a separating funnel? If yes, then describe the procedure. If not, explain.
Answer: The mixture of alcohol and water cannot be separated using a separating funnel, since these are not immiscible liquids.
The mixture of alcohol and water can be separated by the process of distillation.
Question: 29. On heating calcium carbonate gets converted into calcium oxide and carbon dioxide.
(a) Is this a physical or a chemical change?
Answer: The conversion of calcium carbonate into calcium oxide and carbon dioxide is a chemical change.
(b) Can you prepare one acidic and one basic solution by using the products formed in the above process? If so, write the chemical equation involved.
Answer: Yes one acidic and one basic solution can be formed by the calcium oxide and carbon dioxide, which are product formed in the above process.
Since metallic oxides are basic and non-metallic oxides are acidic in nature.
Calcium oxide is a metallic oxide. Hence by dissolving it in water a basic solution is formed because of the formation of calcium hydroxide. The reaction involvedCalcium oxide is a metallic oxide. Hence by dissolving it in water a basic solution is formed because of the formation of calcium hydroxide. The reaction involved in this can be written as follows:
CaO + H2O ⇌ Ca(OH)2
Carbon is a non metal hence carbon dioxide is acidic in nature. When it is dissolved in water an acidic solution is formed.
CO2+H2O ⇌ H2CO3
Question: 30. Non metals are usually poor conductors of heat and electricity. They are non-lustrous, non-sonorous, non-malleable and are coloured.
(a) Name a lustrous non-metal.
(b) Name a non-metal which exists as a liquid at room temperature.
(c) The allotropic form of a non-metal is a good conductor of electricity. Name the allotrope.
Answer: Graphite. Graphite is a good conductor of electricity. It is an allotropic form of carbon.
(d) Name a non-metal which is known to form the largest number of compounds.
Answer: Carbon is a non-metal. It is known to form the largest number of compounds.
(e) Name a non-metal other than carbon which shows allotropy.
Answer: Sulphur is a non-metal which shows allotropy. Disulphur and trisulphur are some of the allotropes of sulphur.
(f) Name a non-metal which is required for combustion.
Question: 31. Classify the substances given in Figure into elements and compounds
Answer: Elements: Cu, Zn, O2, F2, Hg, Diamond
Compound: CaCO3, NaCl(aq), H2O,
Question: 32. Which of the following are not compounds?
(a) Chlorine gas
(b) Potassium chloride
(d) Iron sulphide
(h) Carbon monoxide
(i) Sulphur powder
Answer: Chlorine gas, iron, aluminium, iodine, carbon and sulphur powder are not compounds.
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