NCERT IN-TEXT QUESTIONS SOLVED
1. Give an example of a metal which
(i) is a liquid at room temperature.
(ii) cart be easily cut with knife.
(iii) is the best conductor of heat.
(iv) is a poor conductor of heat.
Ans. (i) Mercury (Hg)
(ii) Sodium and potassium
(iii) Silver and copper
(iv) Lead -.
2. Explain the meanings of malleable and ductile.
Ans. Malleable: A metal is said to be malleable if it can be beaten into thin sheets, e.g. silver and gold are the best malleable metals.
Ductile: A metal is said to be ductile when it can be drawn into thin wires, e.g. silver and gold are the best ductile metals.
3. Why is sodium kept immersed in kerosene oil?
Ans. Sodium is highly reactive metal. It reacts with oxygen in air at room temperature, the reaction is highly exothermic. To prevent this sodium is kept preserved under kerosene. Sodium does not react with kerosene.
4. Write equations for the reactions of
(i) iron with steam
(ii) calcium and potassium with water
Ans. (i) Iron with steam
5. Samples of four metals A,B, C and D were taken and added to the following solutions one by one. The results obtained have been tabulated as follows.
Use the table above to answer the following questions, about metals A, B, C and D.
(i) Which is most reactive metal?
(ii) What would you observe if B is added to a solution of copper (II) sulphate?
(iii) Arrange the metals A, B, C and D in the order of .decreasing reactivity?
Ans. (i) B is most reactive.
(ii) Blue colour of copper sulphate solution disappears’ arid-reddish brown copper metal is deposited on the metal B.
(iii) B > A > C > D is the order of reactivity.
6. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron’ reacts with dilute H2SO4.
Ans. When a reactive metal reacts with hydrochloric acid hydrogen gas is produced A reactive metal displaces the hydrogen from acid and release hydrogen gas.
Fe(s) .+ dil H2SO4(aq) → FeSO4(aq) + H2(g)
7. What would your observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place.
Ans. Zinc is more reactive than iron, hence when added‘ to iron (II) sulphate, it can displace iron metaliand the colour of solution fades from green to colourless due to formation of zinc sulphate. The greyish black iron metal gets deposited.
8. (i) Write the electron dot structures for sodium, oxygen and magnesium.
(ii) Show the formation of Na2O and MgO by the transfer of electrons
(iii) What are the ions present in these compounds?
9. Why do ionic compounds have high melting points?
Ans. Ionic compounds are made up of two opposite charged ions i.e., cations (+) and anions (�), which are held together with strong electrostatic force of attraction. To break this strong bonding into ions, large amount of heat energy is required, hence the melting point of ionic compounds is high.
10. Define the following terms:
(i) Mineral (ii) Ore (iii) Gangue
Ans. (i) Mineral: The naturally occurring chemical substance which ,contains metals with, some other elements: or impurities is called mine*,
(ii) Ore: The minerals from which metals can be extracted economically on large scale are called ores.
(iii) Gangue: The impurities present in ore/minerals are called gangue.
11. Name two metals which are found in nature in free state.
Ans. Gold, platinum and silver.
12. What chemical process is used for obtaining a metal from oxide?
Ans. To obtain metals from its oxides for metals of medium reactivity one can use carbon as reducing agent and the chemical process is called reduction. Also; displacement reaction is used in which highly reactive metal acts as reducing agent. !But for the metals of high reactivity the method of electrolytic reduction in used.
e.g., 3MnO2(s) + 4Al(s) → 3Mn(l) + 2Al2O3(s) + heat
13. Metallic oxides of zinc, magnesium and copper were heated with the following metals.
In which cases will you find displacement reactions take place?
14. Which metals do not corrode easily?
Ans. Metals which are less reactive and lie at the bottom of reactivity series i.e., silver, gold, platinum do not react with atmospheric gases and hence do not corrode easily.
15. What are alloys?
Ans. Alloys are homogeneous mixture of two or more� metals or metals or metal and non-metal.
e.g., Brass � Cu + Zn
metal + metal
Bronze � Cu + Zn
metal + metal
Steel � Fe + Ni + Cr + C
metals + non-metal
QUESTIONS FROM NCERT TEXTBOOK
1. Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal (b) MgCI2 solution and aluminium metal
(c) FeSO4 solution and silver metal (d) AgNO3 solution and copper metal
Ans. (a) Cu cannot displace Na → No reaction
(b) Al cannot displace Mg → No reaction
(c) Ag cannot displace Fe → No reaction
(d) Cu can displace Ag → Reaction takes place
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.
Ans. (c) Applying a coating of zinc
3. An element reacts with oxygen to giver a compound with a high melting point. This compound is also soluble in water. This element is likely to be
(a) calcium (b) carbon (c) silicon (d) iron
Ans. (a) Calcium.
4. Food cans are coated with tin and not with zinc because
(a) zinc is costlier then tin. (b) zinc has higher melting point than tin.
(c) zinc is more reactive than tin (d) zinc is less reactive than tin.
Ans. (c) zinc is more reactive, than tin.
5. You are given a hammer, a battery, a bulb, wires and. witch.
(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.
Ans. (a) To distinguish between samples-of- metals and non-metals one can use hammer to beat the given material into sheets, if it breaks it is non-metal but if it is beaten into thin sheets it is a metal.
One can also use battery, wires, bulb and switch to make a circuit and use the given material to complete the circuit one by one, if the electric current flows and the bulb glows then it is metal and if not then it is non-metal.
(b) Though these tests gives us rough ideas in distinguishing between metals and non-metals but they are not reliable because both in metals & non-metals there are exceptions. For example Na metal is brittle and graphite can show conductivity.
6. What are amphoteric oxides? Give two examples of amphoteric oxides.
Ans. The oxides which behave as acid as well as base are called amphoteric oxides e.g., Al2O3 and ZnO are amphoteric oxides; they both react with acid as Well as base to give salt and water.
7. Name two metals which will displace hydrogen from dilute acids and two metals which will not.
Ans. Metals which lie above Hydrogen in the activity series ie. Zn, Al, Mg can displace hydrogen from dilute acids, because they are more reactive than H2. Metals which lie below hydrogen in the activity series i.e. Cu, Ag, Au cannot displace hydrogen from dilute acids, because they are less reactive than hydrogen.
8. In the electrolytic refining of M, what would you take as the anode, the cathode and the electrolyte?
Ans. For electrolytic refining of M:
Impure metal M → will be anode
Pure sample of M → will be cathode
Electrolyte → Acidified, soluble salt of 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 the balanced chemical equation for the reaction taking place.
Ans. (a) (i) There will be no effect of gas on dry litmus paper.
(ii) Moist blue litmus paper turns red.
(b) (i) S + O2 → SO2
(ii) SO2 + H2O → H2SO3
10. State two ways to prevent the rusting of iron.
Ans. (i) Rusting can be prevented by painting iron articles so that iron surface does not come in contact with air and moisture required for rusting.
(ii) By coating iron articles with a protective layer of zinc metal i.e. by galvanization which prevents the rusting of iron.
11. What type of oxides are formed when non-metals combine with oxygen?
Ans. When non-metals combine with oxygen they form acidic oxides. E.g. SO2, CO2, NO2. [In some cases it also form neutral oxide e.g., H2O, CO]
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 highly reactive metal, yet it Is used to make utensils for coking.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
Ans. (a) Au, Ag and Pt are highly lustrous, malleable and ductile, so. they are used in making jewellery.
(b) Na, K and Li are highly reactive matals, they react with oxygen present in air at room temperature and catches �fire in presence 8foistu�re. They don�t react with oil (kerosene), hence stored in oil.
(c) Aluminium form a very protective layer of Aluminium (Al2O3) oxide on its surface which protects it from corrosion (or reaction with any food item).
(d) Reduction of metal oxides to metal is cheaper and easier than the reduction of carbonate and sulphide ores. So carbonate and sulphide ores are first converted to metal oxide and then further reduced to form metals.
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 vessel?
Ans. Copper metal corrodes to form copper carbonate and get tarnished. On cleaning with lemon or tamarind juice, the acid present in: them dissolves the copper carbonate thereby cleaning the vessel.
14. Differentiate between metal and non-metal on the basis of their chemical properties.
|1. Metals loose electrons .to form positive ions.||Non-metals gain electrons to form negative -ions.|
|2. Metals fon basic oxides.||Nonmetals form acidic oxides.|
|3. Metals scan displace hydrogen from acids.||Non-metals cannot displace hydrogen from acids.|
|4. All metals do not combine with hydrogen to form hydrides (except reactive metals like Na, K, Ca).||All non-metals combine with hydrogen to form hydrides.|
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. The solution is aqua regia (1 part of conc. HNO3 acid and 3 part of conc. HCl acid) is used by the goldsmith, which dissolves gold.
16. Give reason why copper is used to make hot water tanks and not steel (an alloy of iron).
Ans. Copper is a good conductor of heat as compared to steel.