NCERT Solutions for Class 10 Science Chapter 3 Metals And Non Metals

Q1 )

Which of the following pairs will give displacement reactions?

• (a) NaCl solution and copper metal
• (b) \( MgCl_2 \) solution and aluminium metal
• (c) \(FeSO_4 \) solution and silver metal
• (d)\( AgNO_3 \) solution and copper metal.

Answer :

To solve this question, we should first remember the definition of displacement reaction which states that those reactions where a more reactive element displaces/removes a less reactive element is called displacement reaction. Now let's look at each option one by one.


(a) NaCl solution and copper metal - In order for this reaction to complete copper(Cu) must replace Na(sodium) but this is not possible as copper is less reactive than sodium(see reactivity series)


(b)\( MgCl_2 \) solution and aluminium metal - Here, aluminium(Al) must replace magnesium(Mg) but it is not possible as aluminium(Al) is less reactive than magnesium(Mg)


(c)\(FeSO_4 \) solution and silver metal -Here, Ag(Silver) must replace Fe(Iron) but it is not possible


(d) \( AgNO_3 \) solution and copper metal - Yes, this reaction is possible as copper(Cu) is more reactive than silver(Ag) so, cu(copper) metal will easily displace Ag and reaction will be


\( AgNO_3 + Cu \Rightarrow Cu(NO_3)_2 +Ag \)

Q2 )

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 the above

Answer :

The most suitable way of preventing an iron frying pan from rusting is applying a coating of zinc. This process is also called galvanisation.

Applying grease(a) and applying paint(b) are also one of the ways to prevent iron frying pan from rusting but it is not the most best possible way as grease and paint can be eroded/removed while heating or cleaning iron frying pan but on the other hand coating of zinc will be sustained for a longer duration.

Q3 )

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 :

The Element is likely to be Calcium (Option a)

Calcium react with oxygen and gives calcium oxide which has a high melting point of 2,572 celsius and it is also soluble in water

Let us look at other options :
Option b - carbon reacts with oxygen to give carbon dioxide which is a gas. So, this option is wrong.
Option c - silicon reacts with oxygen to form silicon oxide which is insoluble in water .So, the option is wrong
Option d - iron reacts with oxygen to form iron(iii) oxide which is insoluble in water.So,the option is wrong

Q4 )

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 zinc because zinc is more reactive than tin. So, option c is correct.

We should not use zinc in food cans as they are more reactive and might react with food items present in containers and make them unhealthy and not good for eating.

Q5 )

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.

Answer :

(a)
If the substance can be hammered to convert into sheets then it is metal if it is broken into pieces then it is non-metal. Set up the arrangement using bulb, battery, wire and switch as shown in figure. Place the substance between Point A and B if the bulb starts glowing then the substance is a Metal otherwise it is non-metal because metals are good conductor of electricity.
(b)
Generally above methods can be used to identify metals and non-metals. But there are some exceptions also for example Sodium is metal which is not malleable in fact it is brittle. Graphite allotrope of non-metal carbon is a good conductor of electricity.

Q6 )

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

Answer :

Those oxides that behave as both acidic and basic oxides are called amphoteric oxides. Examples: aluminium oxide (Al2O3), zinc oxide (ZnO)

Q7 )

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

Answer :

Iron and aluminium will displace hydrogen from dilute acids as they more reactive then hydrogen. Mercury and copper cannot displace hydrogen from dilute acids as they are less reactive than hydrogen.

Q8 )

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

Answer :

: During electrolytic refining, impure metal is made anode and a thin strip of pure metal M is made cathode and the electrolyte used is the soluble salt of Metal M which is to be refined.
For example -if impure copper needs to be refine then set up is in the way

Q9 )

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 ?
• (d)Write a balanced chemical equation for the reaction taking place.

Answer :

(a)
(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.

(b)
$$ S(s) + O_{2}(g) \rightarrow SO_{2}(g) $$

Q10 ) State two ways to prevent the rusting of iron.

Answer :

Two ways to prevent the rusting of iron are:

Oiling, greasing, or painting: 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. Hence, rusting is prevented.

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.

Q11 )

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

Answer :

When non-metals are combined with oxygen then neutral or acidic oxides are formed. Examples of acidic oxides are NO2, SO2 and examples of neutral oxides are NO, CO etc.

Q12 )

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 :

Q13 ) 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 :

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 neutralises the basis copper carbonate and dissolves the layer. That is why, tarnished copper vessels are cleaned with lemon or tamarind juice to give the surface of the copper vessel its characteristic lustre.

Q14 ) Differentiate between metal and non-metal on the basis of their chemical properties

Answer :

Q15 ) 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 :

Aqua regia is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ration 3:1.It can dissolve gold. It is a corrosive fuming liquid. That's why it is used to clean gold and platinum too. And after cleaning gold along with impurities, it will shine but its weight become slightly less.

Q16 ) 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 (an alloy of iron), then iron would react vigorously with the steam formed from hot water. $$ 3Fe + 4H_{2}O \rightarrow Fe_{3}O_{4}+H_{2}O $$
That is why copper is used to make hot water tanks, and not steel.