1) Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal
(b) MgCl2 solution and aluminium metal
(c) FeSO4 solution and silver metal
(d) AgNO3 solution and copper metal.
ANSWER:-AgNO3 solution and copper metal will give displacement reaction.
2) Which of the following methods is suitable for preventing an iron frying pan from rusting?
(a) Applying grease
(b) Applying paint
(c) Applying a coating of zinc
(d) all of the above.
ANSWER:-Applying a coating of zinc.
3) An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be
4) Food cans are coated with tin and not with zinc because
(a) zinc is costlier than tin.
(b) zinc has a higher melting point than tin.
(c) zinc is more reactive than tin.
(d) zinc is less reactive than tin.
ANSWER:- Food cans are coated with tin and not with zinc because zinc is more reactive than tin.
5) You are given a hammer, a battery, a bulb, wiresand a switch.
(a) How could you use them to distinguish between samples of metals and non-metals?
(b) Assess the usefulness of these tests in distinguishing between metals and nonmetals.
ANSWER:-a)We can beat the sample with hammer and if it can be beaten into thin sheets then its a metal otherwise a nonmetal. Similarly, the battery,bulb, wires, and a switch arrange to set up a circuit with the sample. If the sample conducts electricity, then it is a metal otherwise a non-metal.
b) It is useful in distinguishing between metal and non metals.
6)What are amphoteric oxides? Give two examples of amphoteric oxides.
ANSWER:-Oxides of metals which have both acidic as well as basic behaviour are known as amphoteric oxides.
Examples:- aluminum oxide (Al2O3), zinc oxide (ZnO)
7) Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
ANSWER:-Sodium and Potassium will displace hydrogen from dilute acids as they more reactive than hydrogen. Metals that are less reactive than hydrogen do not displace it for example: copper and silver.
8) In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
ANSWER:-In the electrolytic refining of a metal M:
Anode → impure metal M
Cathode → thin strip of pure metal M
Electrolyte → Solution of salt of the metal M
9 ) Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below. (Refer to the book)
(a) What will be the action of gas on
(i) dry litmus paper?
(ii) moist litmus paper?
(b) Write a balanced chemical equation for the reaction taking place.
ANSWER:- (i) There will be no action on dry litmus paper.
(ii) The colour of litmus paper will turn red because sulphur is a non-metal and the oxides of non-metal are acidic in nature.
10) State two ways to prevent the rusting of iron.
ANSWER:-Two ways to prevent the rusting of iron are:
a) Galvanisation: An iron article is coated with a layer of zinc metal, which prevents the iron to come in contact with oxygen and moisture. Hence, rusting is prevented.
b) By making alloys
11) What type of oxides is formed when non-metals combine with oxygen?
ANSWER: - when non metals combine with oxygen it forms acidic oxides.
12) Give reasons.
(a) Platinum, gold and silver are used to make jewellery.
(b) Sodium, potassium and lithium are stored under oil.
(c) Aluminum is a highly reactive metal, yet it is used to make utensils for cooking.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
ANSWER:- a)Platinum, gold and silver are used to make
jewellery because these are low reactive metal and do not corrode easily and hence do not lose their shine and lustre.
c) The reaction of these substances with oxygen is highly exothermic which may cause fire, also they react with water to form base so they are kept in oil.
d) This is because aluminium is good conductor of heat and electricity. To prevent its reaction with food at high temperature a protective layer of aluminium oxide is formed which prevent further corrosion.
e) Carbonate and sulphide ores are usually converted into oxides during the process of extraction because metals can be easily extracted from their oxides rather than from their carbonates and sulphides.
13) You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
ANSWER:-The citric acid present in the lemon or tamarind neutralises the basis copper carbonate and dissolves the layer formed due to corrosion and gives the surface of the copper vessel its characteristic lustre.
14) Differentiate between metal and non-metal on the basis of their chemical properties.
Oxides of metals are basic in nature.
Oxides of nonmetals
are acidic in nature
Metals are electropositive.
Non metals are electronegative
They act as reducing agents.
They act as oxidising agents
Metals form chlorides which are electrovalent or ionic compounds.
Non metals form chlorides which
are covalent compounds
15) A man went door to door posing as a goldsmith.
He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?
ANSWER:-The solution he had used was Aqua regia which is a 3:1 mixture of conc. HCl and conc. HNO3.Aqua regia is a fuming, highly corrosive liquid. It dissolves gold in it. Since the outer layer of the gold bangles is dissolved in aqua regia so their weight was reduced drastically.
16) Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
ANSWER:-Copper does not react with cold water, hot water or steam. However, iron reacts with steam. If the hot water tanks are made of steel. So, copper is used to make hot water tanks.