Question 1: Which of the following can be beaten into thin sheets?
Question 2: Which of the following statements is correct?
Question 3: Fill in the blanks:
Answer: (a) reactive, (b) electricity, (c) more, (d) hydrogen
Question 4: Mark T if the statement is true and F if it is false.
Answer: (a) F, (b) T, (c) F, (d) F
Question 5: Some properties are listed in the following Table. Distinguish between metals and non-metals on the basis of these properties.
|Heat conduction||Conductor of heat||Non-conductor of heat|
|Conduction of electricity||Conductor of electricity||Non-conductor of electricity|
Question 6: Give reasons for the following:
(a) Aluminium foils are used to wrap food items.
Answer: Aluminium reacts with air to make a coating of aluminium oxide on it. This layer prevents aluminium from further reactions with any substance. Due to this, aluminium foils are used to wrap food items because it does not react with food.
(b) Immersion rods for heating liquids are made up of metallic substances.
Answer: Metals are good conductors of heat and have a high melting point. Immersion rods need to heat up quickly and should not melt at high temperature. Hence, immersion rods for heating liquids are made up of metallic substances.
(c) Copper cannot displace zinc from its salt solution.
Answer: Copper is less reactive than zinc. Hence, copper cannot displace zinc from a compound of zinc.
(d) Sodium and potassium are stored in kerosene.
Answer: Sodium and potassium are highly reactive and react vigorously with water even at room temperature. The reaction is highly exothermic and the reaction mixture instantly catches fire. Sodium and potassium are stored in kerosene to prevent this reaction and to prevent accidental fire.
Question 7: Can you store lemon pickle in an aluminium utensil? Explain.
Answer: We know that metals react with acids to produce hydrogen gas. Lemon pickle contains a high amount of acid and the acid can easily react with aluminium. Hence, lemon pickles should not be stored in aluminium utensils.
Question 8: In the following Table some substances are given in Column I. In Column II some uses are given. Match the items in column I with those in Column II.
|Column I||Column II|
|(a) Gold||(1) Thermometers|
|(b) Iron||(2) Electric wire|
|(c) Aluminium||(3) Wrapping food|
|(d) Carbon||(4) Jewelry|
|(e) Copper||(5) Machinery|
|(f) Mercury||(6) Fuel|
Answer: (a) 4, (b) 5, (c) 3, (d) 6, (e) 2, (f) 1
Question 9: What happens when
(a) Dilute sulphuric acid is poured on a copper plate?
Answer: Copper does not react with dilute sulphuric acid. So, no reaction takes place when dilute sulphuric acid is poured on a copper plate. But when concentrated sulphuric acid is poured over copper plate, effervescence is observed. This happens because of formation of hydrogen gas.
Cu + H2SO4 → CuSO4 + H2
(b) Iron nails are placed in copper sulphate solution? Write word equations of the reactions involved.
Answer: When iron nails are placed in copper sulphate solution, the blue colour of copper solution is replaced by a light green colour. This happens because iron; being more reactive than copper; displaces copper from copper sulphate and makes iron sulphate.
CuSO4 + Fe → FeSO4 + Cu
Question 10: Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.
(a) How will she find the nature of the gas?
Answer: Saloni should bring a wet litmus paper (blue) near the evolved gas. When litmus paper turns to red it indicates that the evolved gas is acidic in nature.
(b) Write down word equations of all the reactions taking place in this process.
Answer: Carbon (in charcoal) reacts with oxygen to produce carbon dioxide gas.
C + O2 → CO2
Carbon dioxide reacts with water to form carbonic acid.
CO2 + H2O → H2CO3
Question 11: One day Reeta went to a jeweller’s shop with her mother. Her mother gave old gold jewellery to the goldsmith to polish. Next day when they brought the jewellery back, they found that there was a slight loss in its weight. Can you suggest a reason for the loss in weight?
Answer: Jewelers use Aqua Regia to clean jewelry. Gold is an inert metal which does not react with acids. But Aqua Regia is a mixture of hydrochloric acid and nitric acid in 3 : 1 ratio. It is so potent that it even dissolves gold and silver. Some of the gold is thus lost during cleaning of jewelry. This explains the weight loss of jewelry.
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