NCERT SOLUTIONS SCIENCE TENTH STANDARD: 3. Metals and Non-metals

CHAPTER 3.
METALS AND NON-METALS
PAGE No: 40

1. Give an example of a metal which

(i) is a liquid at room temperature

Mercury

(ii) can be easily cut with a knife

Sodium and Potassium

(iii) is the best conductor of heat

Silver and Copper

(iv) is a poor conductor of heat

Lead and Mercury

2. Explain the meaning of malleable and Ductile?

Malleable : The property of metals by which , it can be beaten into thin sheets
The most malleable metals are Gold and Silver

Ductile : The property of metals by which , it can be drawn into thin wires
The most ductile metal is Gold . From one gram of gold a wire of 2 km can be drawn.

PAGE No: 46

1. Why is sodium kept immersed in kerosene oil?

Sodium is a highly reactive metal. It reacts vigorously with oxygen so it cannot be placed open to atmosphere.
If sodium is kept it water it reacts with the dissolved oxygen present in it.
Hence sodium is kept in kerosene oil.

2. Write equations for the reactions of

(i) Iron with steam.

3Fe + 4H₂O à Fe₃O₄ + 4H₂

(ii) Calcium and potassium with water

Ca + 2H₂O à Ca(OH)₂ + H₂

2K + 2H₂O à 2KOH + H₂ + Heat energy

3 Samples of four metals A, B,C and D were taken and added to the following solutions one by one . The result obtained have been tabulated as follows

Metal	Iron (ll) sulphate	Copper (ll) sulphate	Zinc sulphate	Silver nitrate
A	No reaction	Displacement
B	Displacement		No reaction
C	No reaction	No reaction	No reaction	Displacement
D	No reaction	No reaction	No reaction	No reaction

Use the table above to answer the following questions about metals A, B,C and D

(i) Which is the most reactive metal?

B is the most reactive metal.
According to the reactivity series the order of reactivity is Zinc sulphate > Iron (ll) sulphate > Copper (ll) sulphate > Silver nitrate.
No metal has reaction with Zinc sulphate
Second is Iron (ll) sulphate, and metal B displaces it , Hence B is the most reactive metal.

* Metal A does not react with Zinc sulphate as it has no reaction with Iron (ll) sulphate which is below zinc in the reactivity series.

(ii) What would you observe if B is added to a solution of Copper(ll) sulphate?

Metal B displaces copper from its solution of Copper (ll) sulphate. Since metal B displaced iron which is above copper in the reactivity series

(iii)Arrange the metals A,B,C and D in the order of decreasing reactivity

B > A > C > D

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

Hydrogen gas is produced when dilute hydrochloric acid is added to a reactive metal.

Fe + H₂SO₄ à Fe SO₄ + H₂

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

When zinc is added to a solution of iron(ll) sulphate zinc would displace iron from its solution.
This is because zinc is above iron in the reactivity series

Zn + FeSO₄ à Fe + ZnSO₄

PAGE No: 49

1. (i) Write the electron dot structures for sodium, oxygen and magnesium.

(ii)Show the formation of Na₂O and MgO by the transfer of electrons

Na₂O

Na₂O contains Sodium and oxygen as its constituent elements.
The atomic number of sodium is 11 and oxygen is 8.
The electronic configurations are 2, 8, 1 and 2, 6 respectively.
For sodium to attain stability it should either loose one electron or gain seven electrons. Gaining of seven electrons is impossible so it looses one electron and becomes stable

Na - 1e^-à Na⁺

For oxygen to attain stability it should either loose six electron or gain two electrons. Loosing of six electrons is impossible so it gains two electrons and becomes stable

O + 2e^-à O^2-

MgO

MgO contains Magnesium and oxygen as its constituent elements.
The atomic number of magnesium is 12 and oxygen is 8.
The electronic configurations are 2, 8, 2 and 2, 6 respectively.
For magnesium to attain stability it should either loose two electrons or gain six electrons. Gaining of six electrons is impossible so it looses two electrons and becomes stable

Mg - 2e^-à Mg²⁺

For oxygen to attain stability it should either loose six electron or gain two electrons. Loosing of six electrons is impossible so it gains two electrons and becomes stable

O + 2e^-à O^2-

(iii) What are the ions present in these compounds?

Na₂O contains O^2- and Na⁺ ions

MgO contains O^2- and Mg⁺² ions

2. Why do ionic compounds have high melting points?

The strong electrostatic force of attraction between the atoms of a molecule are responsible for the high melting points of ionic compounds.

Large amount of energy is required to overcome this force.

PAGE No: 53

1. Define the following terms

(i) Mineral

The elements or compounds which occurs naturally on the earths crust are known as minerals.

(ii) Ore

Minerals which contain a very high percentage of a particular metal , and the metal can be profitably extracted are known as ores.

(iii) Gangue

Ores mined from the earth are contaminated with large amount of impurities such as soil,sand etc. These impurities are called gangue

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

Gold, Platinum and Silver

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

Reduction is the process used to obtain metal from its oxide ore.

PAGE No: 55

1. Metallic oxides of Zinc , magnesium and copper were heated with the following metals

Metal	Zinc	Magnesium	Copper
Zinc Oxide
Magnesium Oxide
Copper oxide

In which case will you find displacement reactions taking place?

Magnesium displaces zinc from its oxide
Nothing will happen with magnesium oxide
Copper would be displaced by zinc and magnesium from its oxides

2. Which metal do not corrode easily?

Gold and platinum

3. What are alloys?

An alloy is a homogeneous mixture of two or more metals or a metal and a nonmetal.
It is prepared by first melting the primary metal and then dissolving the other elements in it in definite proportion.
It is then cooled to room temperature

Eg. Amalgam, Braze, Bronze, Steel

EXERCISES

PAGE No: 56

1. Which of the following pairs will give displacement reaction?

(a) NaCl solution and copper metal

(b) MgCl₂ solution and aluminium metal

(d) AgNO₃ solution and copper metal

2. Which of the following methods is suitable for preventing an iron frying pan from rusting?

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. This element is likely to be

The element is likely to be calcium

4. 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, wire and a switch.

(a) How could you use them to distinguish between samples of metals and non metals?

If we hit with a hammer the metals will get spread due to the property of malleability. On the other hand non metals get powdered and hence we can distinguish a metal and a non metal.

If we connect the samples in a circuit containing a battery, wire , bulb and a switch, the bulb glows if it is a metal because of the property of conductivity. The bulb does not glow if it is a non metal since it is not a conductor of electricity

(b) Asses the usefulness of these tests in distinguishing between metals and nonmetals.

All non metals are not non conductors, for example graphite, an allotrope of carbon

Hammer test is the reliable one for some extent

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

The metal oxides which can neutralize acids and bases

Since it is neutralization reaction the product obtained are salt and water.

Aluminium oxide

Al₂O₃ + 6HCl à 2AlCl₃ + 3H₂O

Al₂O₃ + 2NaOH à 2NaAlO₂ + H₂O

Zinc oxide

ZnO + 2HCl à ZnCl₂ + H₂O

ZnO + 2NaOH à Na₂ZnO₂ + H₂O

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

All the metals above hydrogen in the reactivity series will displace hydrogen from dilute acids
Eg: Lead, Iron, Zinc, Aluminium, Magnesium , Calcium ,Sodium , Potassium etc

All the metals below hydrogen in the reactivity series will not displace hydrogen from dilute acids

Eg: Copper, Mercury, Silver, Gold etc

8. In the electrolytic refining of metal M , what would you take as the anode, the cathode and the electrolyte.

Impure metal which is to be purified is made as the anode.
A thin strip of pure metal (M) as the cathode.
A solution of the metal salt is used as the electrolyte

9. Pratyush took sulphur powder on a spatula and heated it. He collected the heat evolved by inverting a test tube over it.

(a) What will be the action of gas on
(i) Dry litmus paper

Nothing will happen to both the blue and red litmus paper , as it has no moisture content to get ionized

(ii) Moist litmus paper

With moist litmus paper sulphuric acid is produced.

The colour of moist blue litmus chages to red. And no colour change occur to red moist litmus paper

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

S + O₂ à SO₂

SO₂ + H₂O à H₂SO₃( Sulphurous acid)

10. State two ways to prevent the resting of iron

Galvanizing ,Painting , Grezing

11. What types of oxides are formed when non-metals combine with oxygen?

Non metals reacts with oxygen to form acidic oxides or neutral oxides
Eg: SO₂ ( acidic ) H₂O ( neutral )

12. Give Reasons

(a) Platinum, Gold and silver are used to make jewelry.

They are at the bottom of the reactivity series and they do not have reaction with any elements.
They have a shining surface

(b) Sodium, Potassium and Lithium are stored under oil.

They are highly reactive with oxygen and cause fire . It is lighter than water . Hence it is kept under oil.

(c) Aluminium is a highly reactive metal , yet it is used to make utensils for cooking

When exposed to air the metal changes to oxide, aluminium oxide, this get deposited over the surface of the metal and forms a protective coating on the surface. Aluminium oxide is a non reactive compound. Hence aluminium can be used as cooking utensils.

(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction

Metals can be easily obtained from metal oxides by reduction with carbon or any other reducing agents. So metal ores of carbonate and sulphide are first converted into oxides.

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.

Copper vessel forms a greenish coat of basic copper carbonate.
Lemon and tamarind contain mild acid such as citric acid and tartaric acid respectively.
Here a neutralization reaction takes place and the basic coat of copper carbonate is removed

14. Differentiate between metal and nonmetal on the basis of their chemical properties.

Metals	Non Metals
With Oxygen Basic oxides are formed	With Oxygen Acidic / neutral oxides are formed
Displace hydrogen from water	Do not react with water
Displace hydrogen from dilute acids	Do not react with dilute acids
Ionic chlorides are formed	Covalent chlorides are formed
Very few reacts with hydrogen	Almost all reacts with hydrogen
Ionic metal hydrides	Covalent non metallic 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 to hasty retreat. Can you play the detective to find out the nature of the solution he had used ?

Aqua regia

It is a highly corrosive mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio 3: 1

This is the only solution where gold dissolves.

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

Copper is better conductor of heat than steel which is an alloy of iron.
Copper do not react with hot water but iron does