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.
(d) AgNO3 solution and copper metal
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.
(c) applying a coating of zinc.
(We can also apply grease and paint to prevent iron from rusting. However, in case of iron frying pan, grease and paint cannot be applied because when the pan will be heated and washed again and again, the coating of grease and paint would get destroyed.)
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
(a) Calcium (b) Carbon
(c) Silicon (d) Iron
(a) the element is likely to be Calcium.
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.
(c) Zinc is more reactive than tin.
5) You are given a hammer, a battery, a bulb, wires and 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 non – metals.
(a) with the hammer, we can beat the sample and if it can be beaten into thin sheets (that is, it is malleable), then it is a metal otherwise a non-metal. Similarly, we can use the battery, bulb, wires, and a switch to set up a circuit with the sample. If the sample conducts electricity, then it is a metal otherwise a non-metal.
(b) The above tests are useful in distinguishing between metals and non-metals as these are based on the physical properties. No chemical reactions are involved in these tests.
6) What are amphoteric oxides? Give two examples of amphoteric oxides.
Ans: Those oxides that behave as both acidic and basic oxides are called amphoteric oxides.
Eg. Al2O3 and ZnO are amphoteric oxides, they both react with acids as well as bases to give salt and water.
7) Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Ans: Metals that are more reactive than hydrogen displace it from dilute acids.
e.g: sodium and potassium.
Metals that are less reactive than hydrogen do not displace it.
e.g: copper and silver.
8) In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Ans: In the electrolytic refining of a metal M:
Anode → impure metal M
Cathode → thin strip of pure metal M
Electrolyte → acidified 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.
(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.
Ans:(a) (i) There will be no action on dry litmus paper.
(ii) Since the gas is sulphur dioxide (SO2), it turns moist blue litmus paper to red because Sulphur dioxide reacts with moisture to form Sulphurous acid.
(b) (i) O +2 () → 2 () (ii) ℎ 2 () +2 () →23 () ℎ
10) State two ways to prevent the rusting of iron.
Ans: By applying oil, grease, or paint, the surface becomes water proof and the moisture and oxygen present in the air cannot come into direct contact with iron. So, rusting is prevented.
Galvanization: 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.
11) What type of oxides are formed when non-metals combine with oxygen?
Ans: Non-metals combine with oxygen to form 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) Aluminium 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
Ans:(a) Platinum, gold, and silver are used to make jewellery because they are very malleable, ductile and lustrous. Also, they are very less reactive and do not corrode easily.
(b) Sodium, potassium, and lithium are very reactive metals and react very vigorously with air as well as water. Therefore, they are kept immersed in kerosene oil in order to prevent their contact with air and moisture.
(c) This is because Aluminium reacts with oxygen present in air to form a thin layer of Aluminium oxide. This oxide layer protects it from corrosion or any reaction with food. Also, it is light in weight and a good conductor of heat. Hence, it is used to make cooking utensils.
(d) This is because metals can be easily extracted from their oxides rather than from their carbonates or 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.
Ans: Copper reacts with moist Carbon dioxide in air to form copper carbonate and as a result, copper vessel loses its shiny brown surface forming a green layer of copper carbonate. The citric acid present in the lemon or tamarind neutralise the Copper carbonate and dissolves the layer.
14) Differentiate between metal and non-metal on the basis of their chemical properties.
|Metals are electropositive.||Non-metals are electronegative.|
|They react with oxygen to form basic oxides.
These have ionic bonds.
|They react with oxygen to form acidic or neutral oxides.
These have covalent bonds.
|They react with water to form oxides and hydroxides. Some metals react with cold water, some with hot water, and some with steam.||They do not react with water.|
|Some metals react with dilute acids to form a salt and evolve hydrogen gas.||They do not react with dilute acids.|
|They react with the salt solution of metals.||These react with the salt solution of non-metals.|
|They act as reducing agents (as they Can easily lose electrons).||These act as oxidising agents (as they can gain electrons).|
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?
Ans: He must have dipped the gold metal in the solution of aqua regia − a 3:1 mixture of conc. HCl and conc. HNO3. Aqua regia is a fuming, highly corrosive liquid. It dissolves gold in it. After dipping the gold ornaments in aqua regia, the outer layer of gold gets dissolved and the inner shiny layer appears. That is why the weight of gold ornament reduced.
16) Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Ans: 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 (an alloy of iron), then iron would react vigorously with the steam formed from hot water.