NCERT Solutions Class 10 Science
The NCERT Solutions in English Language for Class 10 Science Chapter – 3 (Metals and Non-Metals) has been provided here to help the students in solving the questions from this exercise.
Chapter – 3 (Metals and Non-Metals)
Questions
1. Give 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 the poorest conductor of heat.
Answer –
(a) is a liquid at room temperature – Mercury
(b) can be easily cut with a knife – Sodium
(c) is the best conductor of heat – Silver
(d) is the poorest conductor of heat. – Lead.
2. Explain the meaning of malleable and ductile.
Answer –
Malleable : Substances that can be beaten into thin sheets are called malleable. For example, most of the metals are malleable.
Ductile : Substances that can be drawn into thin wires are called ductile. For example, most of the metals are ductile.
Questions
1. Why is sodium kept immersed in kerosene oil ?
Answer – Sodium and potassium are very reactive metals and and combine explosively with air as well as water. Hence, they catch fire if kept in open. Therefore, to prevent accidental fires and accidents, sodium is stored immersed in kerosene oil.
2. Write the equations for the reactions of
(a) iron with steam
(b) calcium with water
(c) potassium with water.
Answer:
(a) 3Fe(s) + 4H2O (steam) → Fe3O4(s) + 4H2(g)
(b) Ca(s) + 2H2O(aq) ———–> Ca(OH)2(s) +H2(g)
(c) 2K(s) + 2H2O(aq) ———–> 2KOH(aq) + H2(g)
3. Samples of four metals A, B, C and D were taken and were added to the following solutions one by one. The results obtained have been tabulated as follows :
| Metal | Iron(II) sulphate | Copper(II) 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 given above to answer the following questions :
(a) Which is the most reactive metal ?
(b) What would you observe when B is added to solution of copper(II) sulphate ?
(c) Arrange the metals A, B, C and D in order of increasing reactivity. (CBSE 2011)
Answer – Based on the activity series, the relative position of the metals in which involved in solutions is : Zn > Fe > Cu > Ag. On the basis of the results given in the table .
- Metal A is more reactive than copper and less reactive than iron.
- Metal B is more reactive than iron and less reactive than zinc. –
- Metal C is only more reactive than silver and less reactive than other metals.
- Metal D is the least reactive in nature.
In the light of above information, we can conclude that
(a) Metal B is the most reactive.
(b) Since B is more reactive than iron, it is also more reactive than copper. This means that it would displace copper from copper(II) sulphate solution. The blue colour of solution will slowly fade.
(c) The decreasing order of reactivity of metals is: B > A > C > D.
4. Which gas is produced when a reactive metal reacts with dilute hydrochloric acid ? Write the chemical reaction when iron reacts with dilute H2SO4.
Answer – Hydrogen gas (H2) is produced when a reactive metal reacts with dilute hydrochloric acid. Iron and dilute H2SO4 react as follows :
Fe(s) + H2SO4(aq) ⟶ FeSO4(aq) + H2(g)
Hydrogen gas is evolved in this reaction also.
5. What would you observe when zinc is added to a solution of iron (II) sulphate ? Write the chemical reaction that takes place. (CBSE 2010)
Answer – The green colour of the solution would slowly disappear. Zinc would gradually dissolve and iron would get precipitated at the bottom of the beaker.
Zn(s) + FeSO4(aq) ⟶ ZnSO4(aq) + Fe(s)
Questions
1. (i) Write electron-dot structures for sodium, magnesium and oxygen.
(ii) Show the formation of Na2O and MgO by the transfer of electrons.
(iii) What are the ions present in these compounds ?
Answer –
(i)
(ii) Formation of sodium oxide (Na2O)
Formation of magnesium oxide (MgO)
(iii) For answer, consult structures given above.
2. Why do ionic compounds have high melting points?
Answer – Ionic compounds have strong electrostatic forces of attraction between the ions. Therefore, it requires a lot of energy to overcome these forces. That is why ionic compounds have high melting points.
Questions
1. Define the following terms :
(i) Minerals
(ii) Ores
(iii) Gangue.
Answer –
(i) Minerals : These are the combined states of metals and non-metals present in earth’s curst.
(ii) Ores – The minerals from which metals can be conveniently and profitably extracted, are called ores.
(iii) Gangue – It represents the earthy impurities such as mud, sand and clay associated with the ore.
2. Name two metals which are formed in nature in free state.
Answer – The metals are gold (Au) and platinum (Pt).
3. Which chemical process is used for obtaining a metal from its oxide ?
Answer – The chemical process is known as reduction.
Questions
1. Metallic oxides of zinc, magnesium and copper were heated with the following metals. In which cases, will you find displacement reactions taking place ?
| Metal | Zinc | Magnesium | Copper |
| Zinc Oxide | |||
| Magnesium Oxide | |||
| Copper Oxide |
Relative positions of these metals in the activity series are : Mg, Zn, Cu : In the light of this :
Answer –
| Metal | Zinc | Magnesium | Copper |
| Zinc Oxide | No Reaction | Displacement | No Reaction |
| Magnesium Oxide | No Reaction | No Reaction | No Reaction |
| Copper Oxide | Displacement | Displacement | No Reaction |
2. Which metals do not corrode easily ?
Answer – Metals such as gold (Au) and platinum (Pt) present at the bottom of the activity series do not corrode easily.
3. What are alloys ?
Answer – Alloys are the homogeneous mixture of two or more metals or even metals and non-metals.
Exercise
1. Which of the following 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.
Answer – (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 the above.
Answer – (c) Applying a coating of zinc
3. An element reacts with oxygen to give a compound with high melting point. This compound is also water soluble. The element is likely to be :
(a) Calcium
(b) Carbon
(c) Silicon
(d) Iron
Answer – (a) Calcium
4. Food cans are coated with tin and not with zinc because
(a) Zinc is costlier than tin
(b) Zinc has higher melting point than tin
(c) Zinc is more reactive than tin
(d) Zinc is less reactive than tin.
Answer – (c) Zinc is more reactive than tin
5. You are given a hammer, a battery, a bulb, wires and a switch :
(a) Flow could you use them to distinguish between samples of metals and non metals ?
Answer – 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) Assess the usefulness of these tests to distinguish between metals and non metals.
Answer – 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 examples of two amphoteric oxides.
Answer – Those oxides that behave as both acidic and basic oxides are called amphoteric oxides. Examples: aluminium oxide , zinc oxide.
7. Name two metals which can displace hydrogen from dilute acids and two metals which can not do so.
Answer – Sodium and calcium can displace hydrogen from dilute acids Copper and silver can not displace hydrogen from dilute acids.
8. In the electrolytic refining of metal M, name anode, cathode and electrolyte.
Answer –
Anode : Rod of the impure metal
Cathode : Rod of pure metal
Electrolyte : Aqueous solution of 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 the figure.
(a) What will be the action of gas on
(i) dry litmus paper ?
Answer – SO2(g) has no action of dry litmus paper.
(ii) moist litmus paper ?
Answer – 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) Write a balanced chemical equation for the reaction taking place.
Answer – The gas evolved upon heating sulphur powder on a spatula is sulphur dioxide
10. State two ways to prevent the rusting of iron.
Answer – Two ways to prevent the rusting of iron are:
1. By applying a coating of grease or paint on the surface of iron.
2. By depositing a layer of zinc on the surface of iron. The process is called galvanisation.
11. What types of oxides are formed when non-metals combine with oxygen ?
Answer – Non-metals combine with oxygen to form acidic oxides.
For example:
12. Give reasons for the following :
(a) Platinum, gold and silver are used to make jewellery.
Answer – Platinum, gold, and silver are used to make jewellery because they are very lustrous. Also, they are very less reactive and do not corrode easily.
(b) Sodium, potassium and lithium are stored under oil.
Answer – Reaction of sodium, potassium and lithium with oxygen is so violent that they catch fire. To prevent accidental fire, they are stored under kerosene oil.
(c) Aluminium is a highly reactive metal but still used for making cooking utensils.
Answer – This is because aluminum is a good conductor of heat. Aluminum forms a layer of aluminum oxide at high temperature which is prevent the further corrosion.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
Answer – It is easier to reduce oxide than the carbonates and sulphide to the 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 vessels.
Answer – Copper, on keeping in air reacts with atmospheric carbon dioxide to form a green layer of copper carbonate. Copper carbonate reacts with citric acid present in lemon or tartaric acid present in tamarind to form soluble copper citrate or copper tartarate. The vessels are thus cleaned using water.
14. Differentiate between metal and non-metal on the basis of their chemical properties.
Answer – Metals and non-metals can be differentiated on the basis of following chemical properties.
15. A man went door to door posing as a goldsmith. He promised to bring back the glitter on dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparked like new but their weight was reduced drastically. The lady got upset and after a futile argument, the man beat a hasty retreat. Can you predict the nature of the solution used by the impositer ?
Answer – Aqua regia, which is a mixture of 3 parts concentrated HCl and part of concentrated nitric acid dissolves gold. The man put the gold bangles in this solution. The outer dirty layer of gold bangles dissolved in aqua regia bring out the shining bangles.
As the outer layer of bangles dissolved in aqua regia, the weight was reduced drastically.
16. Give reason as to why copper is used to make hot water tanks and not steel (an alloy of iron).
Answer – Electrical conductivity of a metal is decreased when it is alloyed with another metal or non-metal. Thus, the electrical conductivity of steel is much less than that of pure. That is why copper is used to make hot water tanks and not steel.
