Q.12. You are given two samples of water labelled as ‘A’ and ‘B’. Sample ‘A’ boils at 100 °C and sample ‘B’ boils at 102 °C. Which sample of water will not freeze at 0 °C? Comment.
Ans. Sample 'B' will not freeze at 0°C as it is impure water because it boils at 102°C. Therefore, it will freeze below 0°C.
Q.13. What are the favourable qualities given to gold when it is alloyed with copper or silver for the purpose of making ornaments?
Ans. Pure gold is soft metal and can change its shape with a little force. Therefore, it is not suitable for making ornaments. When it is alloyed with copper or silver it becomes hard and suitable for making ornaments. Thus, it provides strength to gold.
Q.14. 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
Ans. The element is a metal.
(i) It has metallic lustre.
(ii) It is malleable.
(iii) It is good conductor of heat and electricity.
(iv) It is hard and has high tensile strength.
Q.15. 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.
(b) Two volatile components with appreciable difference in boiling points.
(c) Two immiscible liquids.
(d) One of the components changes directly from solid to gaseous state.
(e) Two or more coloured constituents soluble in some solvent.
Ans. (a) Iodine is separated from sand by sublimation.
(b) Acetone is separated from water by distillation.
(c) Kerosene oil and water are separated by separating funnel.
(d) Camphor by the process of sublimation.
(e) Mixture of inks can be separated by chromatography.
16. Fill in the blanks:
(a) A colloid is a ________ mixture and its components can be separated by the technique known as _______ .
(b) Ice, water and water vapour look different and display different _______ properties but they are_______the same.
(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 .
(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 _______.
(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.
Ans. (a) heterogeneous, centrifugation
(b) physical, chemically
(c) water, chloroform; because water is lighter than chloroform
(d) fractional distillation
(e) scattering, Tyndall effect, colloidal
Q.17. Sucrose (sugar) crystals obtained from sugarcane and beet root are mixed together. Will it be a pure substance or a mixture? Give reasons for the same.
Ans. It will be pure substance because sugar obtained by different sources will have same composition.
Q.18. Give some examples of Tyndall effect observed in your surroundings?
Ans. When a beam of light enters a dark room, its path can easily be seen due to Tyndall effect which is due to scattering light by dust particle present in air.
Q.19. Can we separate alcohol dissolved in water by using a separating funnel? If yes, then describe the procedure. If not, explain.
Ans. No, because alcohol and water form miscible liquids. Separating funnel is used to separate immiscible liquids. Miscible liquids can be separated by the process of distillation. Alcohol and water are best separated by fractional distillation as difference in boiling point is large.
Q.20. On heating calcium carbonate gets converted into calcium oxide and carbon dioxide.
(a) Is this a physical or 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.
Ans. (a) It is a chemical change.
(b) Yes. CaO dissolves in water forming calcium hydroxide which is basic solution.
CaO (s) + H2O (l) → Ca(OH)2 (aq)
CO2(g) dissolves in water forming carbonic acid which is acidic solution.
CO2(g) + H2O (l) → H2CO3 (aq)
Q.21. Non-metals are usually poor conductors of heat and electricity. They are non-lustrous, nonsonorous, 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 which is a good conductor of electricity. Name the allotrope.
(d) Name a non-metal which is known to form the largest number of compounds.
(e) Name a non-metal other than carbon which shows allotropy.
(f) Name a non-metal which is required for combustion.
Q.22. Classify the substances given in figure into elements and compounds
Ans. Elements: Cu, Zn, O2, F2, and Hg, Diamond (carbon)
Compounds: H2O, CaCO3
Q.23. Which of the following are not compounds?
(a) Chlorine gas
(b) Potassium chloride
(d) Iron sulphide
(h) Carbon monoxide
(i) Sulphur powder
Ans. (a) Chlorine gas
(z) Sulphur powder
are elements and not compounds.