Intext Questions Solved

Page 40

Question 1 : Give an example of a metal which

a) is a liquid at room temperature
b) can be easily cut with a knife
c) is the best conductor of heat
d) is a poor conductor of heat

Answer : 

a) Mercury
b) Sodium
c) Silver
d) Mercury

Question 2 : Explain the meanings of malleable and ductile.

Answer :

Malleable . Most of the metals can be beaten into sheets, therefore, they are called malleable, e.g., Al, Cu, Au, Ag are malleable.

Ductile.  Most of the metals can be drawn into wires, therefore, these metals are called ductile, e.g., Cu, Ag, Au, Pt are ductile.

Page 46

Question 1 : Why is sodium kept immersed in kerosene oil?

Answer : It is because sodium metal reacts with air to form sodium oxide which reacts with CO2 to form sodium carbonate. In presence of moisture, it can catch fire.

Question 2 : Write equations for the reactions of 
a) Iron with steam
b) Calcium and potassium with water.

Answer : 

Question 3 : Samples of four metals A, B, C and D were taken and added to 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:
a) Which is the most reactive metal?
b) What would you observe if B is added to a solution of copper (II) sulphate?
c) Arrange the metals, A, B, C and D in the order of decreasing reactivity.

Answer :

a) B is most reactive.
b) Reddish brown copper metal will get deposited and the colour of solution will change.
c) B>A>C>D is order of reactivity.

Question 4 :  Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dil. H2SO4.

Answer : Hydrogen gas is produced.

Fe(s) + H2SO4 (dil.) ———> FeSO4 (aq) + H2 (g)

Question 5 : What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place.

Answer : The solution becomes colourless due to formation of zinc sulphate and greyish black iron metals gets deposited.

Page 49

Question 1 : a) Write the electron-dot structures for sodium, oxygen and magnesium.

b) Show the formation of Na2O and MgO by the transfer of electrons.

c) What are the ions present in these compounds?

Answer : 

Question 2 : Why do ionic compounds have high melting points?

Answer : It is due to strong electrostatic force of attraction between ions due to which high energy is required to separate ionic solids into ions.

Page 53

Question 1 : Define the following terms: a) Mineral, (b) Ore and (c) Gangue.

Answer : a) Mineral : It is rocky material which contains sufficient quantity of minerals so that metal can be extracted profitably.

b) Ore : It is rocky material which contains sufficient quantity of mineral so that metal can be extracted profitably.

c) Gangue : It is rocky material which is present along with the mineral in the ore.

Question 2 : Name two metals which are found in nature in the free state.

Answer :
i) Gold
ii) Silver

Question 3 : What chemical process is used for obtaining a metal from its oxide?

Answer : Reduction.

Page 55

Question 1 : Metallic oxides of zinc, magnesium and copper were heated with the following metals. In which cases will you find displacement reactions taking place?

Answer : In ZnO, no displacement reaction takes place with Zn and Cu, because copper is less reactive than Zn. However, magnesium can displace zinc from zinc oxide.

Mg + ZnO ——-> MgO + Zn

It shows that magnesium is more reactive than zinc.

MgO does not react with Zn, Mg and Cu because Mg is most reactive. Copper oxide undergoes displacement reaction with Zn and Mg as they are more reactive than Cu.

Zn + CuO ——–> ZnO + Cu

Mg + CuO ——-> MgO + Cu

Question 2 : Which metals do not corrode easily?

Answer : Gold, Platinum.

Question 3 : What are alloys?

Answer : They are homogeneous mixture of two or more metals. One of them can be non-metal also.

Text Book Questions Solved

Question 1 : Which of the following pairs will give displacement reactions?
a) NaCl solution with copper metal
b) MgCl2 solution with aluminium metal
c) FeSO4 solution with silver metal
d) AgNO3 solution with copper metal

Answer : d) Cu (s) + 2AgNO3 (aq) ———–> Cu(NO3)2 (aq) + 2Ag

Question 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 : c) Applying a coating of zinc.

Question 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

Answer : a) Calcium.

2Ca + O2 ———> 2CaO

CaO + H2O ————> Ca(OH)2

Question 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 : a) Zinc is costlier than tin.

Question 5 : You are given a hammer, a battery, a blub, wires and a switch.
a) How would 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.

Answer : 

a) Method 1
1. Take an iron metal.
2. Hammer it for long time.
3. Take non-metal like graphite (carbon).
5. Hammer it a little and record your observations.

Observation : Metals change into sheets on hammering whereas non-metals are brittle and they break on hammering.
Conclusion : Metals are malleable whereas non-metals are brittle.

b) Method 2
1. Se the apparatus as shown in the figure below.
2. Take magnesium wire and put it between the clips.
3. Switch on the current and observe the bulb.
4. Now take sulphur powder and put the clips into sulphur poweder.
5. Switch on the current and observe the bulb.

Observation : The bulb glows when the current is switched on in case of magnesium wire. The bulb does not glow in case of sulphur powder.
Conclusion : Metals are good conductor of electricity whereas non-metals are non-conductors of electricity.

These two tests can be used for distinguishing between metals and non-metals. Hammering can be used in most of metals except in case of sodium, potassium, lithium.

Question 6 : What are amphoteric oxides? Give two examples of amphoteric oxides.

Answer : Those oxides which can act as both acidic as well as basic are called amphoteric oxides, e.g., Al2O3, ZnO are amphoteric oxides.

Question 7 : Name two metals which will displace hydrogen from dilute acids, and two metals which will not.

Answer : ‘Zn’ and ‘Al’ will displace hydrogen from dilute acids because they are more reactive than hydrogen. Where Cu and Ag cannot displace hydrogen from dilute acids because they are less reactive than hydrogen.

Question 8 : In the electrolytic refining of a metal ‘M’,  what would you take as the anode, the cathode and the electrolyte?

Answer : Impure metal acts as anode, pure metals acts as cathode. Soluble salt of metal acts as electrolyte.

Question 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 the figure below.

a) What will be the action of gas on
i) dry litmus paper?
ii) moist litmus paper?

b) Write balanced chemical equation for the reaction taking place.

Answer : a) i) There will be no effect of gas on dry litmus paper.
ii) Moist blue litmus paper will turn red.

b) S + O2 ———-> SO2
SO2 + H2O ———-> H2SO3 (Sulphrous acid)

Sulphurous acid turns blue litmus red.

Question 10 : State two ways to prevent the rusting of iron.

Answer : i) Painting : Iron articles are painted so that surface does not come in contact with air and water and it does not get rusted.

ii) Galvanisation : It is process in which iron articles are coated with zinc metal so as to prevent them from rusting. Zinc is more reactive than iron, therefore, it loses electrons more readily and prevents iron from rusting.

Question 11 : What type of oxides are formed when non-metals combine with oxygen?

Answer : Acidic oxides are formed when non-metals combine with oxygen.

Question 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.

Answer : a) It is because they are highly lustrous.
b) They are highly reactive and catch fire in presence of moisture.
c) It is because aluminium forms and oxide layer on its surface which protects it from rusting.
d) It is because it is easier to reduce oxide ore as compared to carbonated and sulphides.

Question 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 : It is because basic copper carbonate formed on copper vessel reacts with acid present in lemon or tamarind juice and gets dissolved and removed.

Question 14 : Differentiate between metals and non-metals on the basis of their chemical properties.

Answer : 

Metals Non-Metals
1. Metals can lose electrons easily forming positive ions. 1. Non-metals can gain electrons easily to form negative ions.
2. Metals form basic oxides. 2. Non-metals form acidic oxides.
3. Metals can displace hydrogen from dilute acids. 3. Non-metals cannot displace hydrogen from dilute acids.
4. Reactive metals can displace hydrogen from water. 4. Non-metals cannot displace hydrogen from water.

Question 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 hastily retreat. Can you play the detective to find the nature of solution he had used?

Answer : The solution was aqua regia. The gold got dissolved in it.

Question 16 : Give reason why copper is used to make hot water tanks and not steel (an alloy of iron).

Answer : Copper is better conductor of heat than steel, therefore, it is used for making hot water tank.