NCERT Solutions for Class 10 Science Chapter 3: Metals and Non-metals
Here you will get simple and reliable answers to all in-text questions and end-of-chapter exercises strictly based on the NCERT textbook for NCERT Class 10 Science Chapter 3: Metals and Non-Metals. These questions are also important for SEBA students.
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Notes on Class 10 Science Chapter 3: Metals and Non-Metals
MCQs on Class 10 Science Chapter 3: Metals and Non-Metals
In-text questions: Page number 40
1. Give an example of a metal which
(i) Is a liquid at room temperature?
(ii) Can be easily cut with a knife?
(iii) Is the best conductor of heat?
(iv) Is a poor conductor of heat?
Answer:
(i) Mercury is the metal that is liquid at room temperature.
(ii) Sodium and potassium are the metals that can be cut with a knife.
(iii) Silver is the best conductor of heat.
(iv) Mercury and lead are poor conductors of heat.
2. Explain the meanings of malleable and ductile.
Answer:
Malleable: A metal that can be beaten into thin sheets is called malleable. This property is called malleability. For example, gold and silver are the most malleable metals.
Ductile: A metal that can be drawn into thin wires is called ductile. This property is called ductility. For example, gold is the most ductile metal.
In-text questions: Page number 46
1. Why is sodium kept immersed in kerosene oil?
Answer:
Sodium is a very reactive metal. It reacts vigorously with oxygen and moisture present in the air, and it can catch fire if kept in the open. Kerosene oil keeps the sodium away from air. So, to prevent accidental fires and protect the metal, sodium is kept immersed in kerosene oil.
2. Write equations for the reactions of:
(i) Iron with steam
(ii) Calcium and potassium with water
Answer:
(i) Iron with steam: Iron does not react with cold or hot water. But it reacts with steam to form iron(II,III) oxide (Fe₃O₄) and hydrogen gas.
3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)
(ii) Calcium with water: Calcium reacts with water to form calcium hydroxide and hydrogen gas. Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal.
Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)
Potassium with water: It reacts violently with cold water. The reaction is so exothermic that the hydrogen catches fire immediately.
2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g) + Heat
3. Samples of four metals A, B, C and D were taken and added to the following solution 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.
1. Which is the most reactive metal?
2. What would you observe if B is added to a solution of Copper (II) sulphate?
3. Arrange the metals A, B, C and D in the order of decreasing reactivity.
Answer:
(i) Metal B is the most reactive because it displaces iron from iron(II) sulphate solution.
(ii) When we add B to copper (II) sulphate solution, a displacement reaction takes place. The blue colour of the copper(II) sulphate solution fades, and a reddish-brown deposit of copper will form on metal B.
(iii)
- B displaces iron, but A does not. So B is more reactive than A.
- A displaces copper, but C does not. So A is more reactive than C.
- C displaces silver, but D displaces nothing. So C is more reactive than D.
Hence, the decreasing order of reactivity is B > A > C > D.
Q4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H₂SO₄.
Answer: Hydrogen gas is produced when dilute hydrochloric acid is added to a reactive metal.
Iron is more reactive than hydrogen. So, when it reacts with dilute sulphuric acid, it replaces hydrogen and forms iron (II) sulphate. Hydrogen gas is released in the process.
Fe(s) + H₂SO₄(aq) → FeSO₄(aq) + H₂(g)
Q5. What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place.
Answer:
Zinc is more reactive than iron. So, zinc is added to a solution of iron (II) sulphate, it displaces iron from the solution. The pale green colour of the solution gradually fades due to the formation of colourless zinc sulphate solution and iron metal is deposited on zinc.
Zn(s) + FeSO₄(aq) → ZnSO₄(aq) + Fe(s)
In-text questions set 3 Page number 49
Q1. (i) Write the electron-dot structures for sodium 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) Electron-dot structures:
- Atomic number of Sodium is 11, so it has the electronic configuration 2, 8, 1. It has 1 valence electron
- Atomic number of Oxygen is 8, so it has the electronic configuration 2, 6. It has 6 valence electrons.
(ii) Formation of Na₂O:
Two sodium atoms (2, 8, 1) each lose their 1 valence electron to achieve a stable octet and become sodium ions (Na⁺). One oxygen atom (2, 6) accepts these 2 electrons, 1 from each sodium atom, to complete its octet and becomes an oxide ion (O²⁻). All the ions now have a stable octet. The Na⁺ and O²⁻ ions have opposite charges. They attract each other and are held by strong electrostatic forces of attraction. In this way, they exist as sodium oxide (Na₂O).
2Na (2, 8, 1) → 2Na⁺ (2, 8) + 2e⁻
O (2, 6) + 2e⁻ → O²⁻ (2, 8)
2Na⁺ + O²⁻ → Na₂O
Formation of MgO:
A magnesium atom (2, 8, 2) gives its two outermost electrons to an oxygen atom. It becomes a magnesium ion (Mg²⁺). The oxygen atom gains these two electrons and becomes an oxide ion (O²⁻). Both ions now have a stable octet and they are held together by strong electrostatic forces.
Mg (2, 8, 2) → Mg²⁺ (2, 8) + 2e⁻
O (2, 6) + 2e⁻ → O²⁻ (2, 8)
Mg²⁺ + O²⁻ → MgO
(iii) Ions present
- Sodium oxide (Na₂O) has sodium ions (Na⁺) and oxide ions (O²⁻).
- Magnesium oxide (MgO) has magnesium ions (Mg²⁺) and oxide ions (O²⁻).
Q2. Why do ionic compounds have high melting points?
Answer:
Ionic compounds are made up of positive and negative ions. There are strong electrostatic forces of attraction between these oppositely charged ions. Therefore, a large amount of heat energy is required to break these forces and melt the compound. This is why ionic compounds have high melting points.
In-text questions: Page number 53
Q1. Define the following terms. (i) Mineral (ii) Ore (iii) Gangue
Answer:
(i) Mineral: The elements or compounds, which occur naturally in the earth’s crust are called minerals.
(ii) Ore: A mineral that contains a very high percentage of a particular metal, and the metal can be profitably extracted from it. These minerals are called ores. Thus, all ores are minerals, but all minerals are not ores.
(iii) Gangue: Ores mined from the earth are mixed with large amounts of impurities such as sand, clay and rocky material. These unwanted impurities are called gangue. These impurities must be removed before extracting the metal.
Q2. Name two metals which are found in nature in the free state.
Answer: Gold (Au) and platinum (Pt) are found in nature in the free state.
Q3. What chemical process is used for obtaining a metal from its oxide?
Answer: The reduction process is used to obtain a metal from its oxide. In this process, oxygen is removed from the metal oxide using a suitable reducing agent such as carbon or a more reactive metal.
For example, zinc oxide is reduced to zinc by heating it with carbon:
ZnO(s) + C(s) Heat→ Zn(s) + CO(g)
The highly reactive metals such as sodium, calcium and aluminium can also act as reducing agents because they can displace metals of lower reactivity from their compounds. For example, aluminium reduces iron(III) oxide to molten iron.
Fe₂O₃(s) + 2Al(s) → 2Fe(l) + Al₂O₃(s) + Heat
In-text questions: Page number 55
Q1. Metallic oxides of zinc, magnesium and copper were heated with the following metals :
| Metal | Zinc | Magnesium | Copper | |
| 1. | Zinc oxide | |||
| 2. | Magnesium oxide | |||
| 3. | Copper oxide |
In which cases will you find displacement reactions taking place ?
Answer:
A more reactive metal can displace a less reactive metal from its oxide. Among the three metals, magnesium is the most reactive, zinc is less reactive, and copper is the least reactive. So the order is Mg > Zn > Cu.
The displacement reactions will take place in the following cases:
| Metal oxide | Zinc | Magnesium | Copper |
|---|---|---|---|
| Zinc oxide | – | Displacement | – |
| Magnesium oxide | – | – | – |
| Copper oxide | Displacement | Displacement | – |
Q2. Which metals do not corrode easily?
Answer:
Gold and platinum do not corrode easily because they are very less reactive metals.
Q3. What are alloys?
Answer:
An alloy is a homogeneous mixture of two or more metals, or of a metal and a non-metal. It is prepared by first melting the main metal and then dissolving the other elements in it in definite proportions. The mixture is then cooled to room temperature so that it solidifies.
For example, bronze is an alloy of copper and tin. Steel is an alloy of iron and carbon.
Chapter-end Exercise questions: Page Number 56-57
Q1. Which of the following pairs 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
Copper is more reactive than silver. So, when copper is added to silver nitrate, copper displaces silver from silver nitrate solution, forming copper(II) nitrate and silver.
Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s)
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 of the above
Answer: (c) Applying a coating of zinc
Applying a coating of zinc creates a protective layer that blocks air and moisture from reaching the iron, thereby preventing rusting. Although grease and paint are common ways to prevent rusting, but they are not suitable for a cooking pan.
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: (a) Calcium
Calcium reacts with oxygen to form calcium oxide (CaO), which is an ionic compound. Ionic compounds have a high melting point. It also dissolves in water to form calcium hydroxide.
2Ca + O₂ → 2CaO
CaO + H₂O → Ca(OH)₂
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: (c) Zinc is more reactive than tin.
Zinc is a more reactive metal, so it can react with the organic acids and moisture present in food items and spoil the food. Tin is less reactive, so it does not react easily with food. That is why we use tin to coat food cans.
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)
- Using the hammer: If we beat the sample with a hammer and if it can be beaten into thin sheets without breaking, then it is a metal, as Metals are malleable. If it breaks into pieces, it is a non-metal, because non-metals are brittle.
- Using the circuit: If we set up a circuit using the battery, bulb, wires and switch, and connect the sample in it. If the bulb glows, the sample conducts electricity, so it is a metal, since metals are good conductors of electricity. If the bulb does not glow, it is a non-metal.
(b) These tests are useful in distinguishing between metals and non-metals because they are based on physical properties such as malleability and electrical conductivity. They help distinguish most metals from non-metals without involving chemical reactions. However, these tests are not completely reliable because some non-metals, such as graphite, can conduct electricity.
Q6. What are amphoteric oxides? Give two examples of amphoteric oxides.
Answer:
Metal oxides that react with both acids and bases to produce salt and water are called amphoteric oxides. They show both acidic and basic behaviour.
Examples: Aluminium oxide (Al₂O₃) and zinc oxide (ZnO).
Q7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Answer:
Metals that are more reactive than hydrogen can displace hydrogen from dilute acids. For example, Zinc (Zn) and magnesium (Mg).
Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)
Mg(s) + H₂SO₄(aq) → MgSO₄(aq) + H₂(g)
Metals that are less reactive than hydrogen cannot displace hydrogen. For example, Copper (Cu) and silver (Ag).
Cu(s) + HCl(aq) → No reaction
Q8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Answer:
- Anode: A thick block of impure metal M.
- Cathode: A thin strip or wire of pure metal M.
- Electrolyte: A suitable salt solution of metal M.
On passing the current through the electrolyte, the metal dissolves from the anode and goes into the solution. An equal amount of pure metal deposits on the cathode. The impurities settle at the bottom as anode mud.
Q9. Pratyush heated sulphur powder on a spatula and collected the gas evolved in an inverted test tube.
(a) What will be the action of the gas on (i) dry litmus paper? (ii) moist litmus paper?
(b) Write a balanced chemical equation for the reaction taking place.
Answer:
When sulphur powder burns in air, it forms sulphur dioxide gas.
S(s) + O₂(g) → SO₂(g)
(a)
(i) Sulphur dioxide gas has no effect on dry litmus paper.
(ii) Sulphur dioxide turns moist blue litmus paper red. This happens because the gas dissolves in the water on the paper and forms sulphurous acid, which is acidic.
(b)
S(s) + O₂(g) → SO₂(g)
SO₂(g) + H₂O(l) → H₂SO₃(aq)
Q10. State two ways to prevent the rusting of iron.
Answer:
Rusting happens when iron comes in contact with air and moisture. We can prevent it in these ways:
- Painting: Iron can be prevented from rusting by coating its surface with rust-proof paints.
- Galvanisation: Rusting can also be prevented by galvanisation, by coating the iron with a thin layer of zinc. The galvanised article is protected against rusting even if the zinc coating is broken.
Q11. What type of oxides are formed when non-metals combine with oxygen?
Answer:
When non-metals combine with oxygen, they form either acidic or neutral oxides.
For example, SO₂ and CO₂ are acidic oxides, while CO is a neutral oxide.
For example: Sulphur burns in oxygen to form sulphur dioxide (SO₂). Sulphur dioxide dissolves in water to form sulphurous acid.
S(s) + O₂(g) → SO₂(g)
SO₂(g) + H₂O(l) → H₂SO₃(aq)
Q12. Give reasons:
(a) Platinum, gold and silver are used to make jewellery.
Answer:
Platinum, gold and silver are used to make jewellery because of the following reasons:
- These metals are used to make jewellery because they are very less reactive and highly resistant to corrosion. They are not easily affected by air, water or most chemicals.
- They are very lustrous (shiny), so they look attractive.
- They are malleable and ductile, so they can be easily shaped into ornaments.
(b) Sodium, potassium and lithium are stored under oil.
Answer:
Sodium, potassium and lithium are highly reactive metals. They react vigorously with oxygen and moisture present in the air and can easily catch fire if left in the open. Oil keeps these metals away from air. So, to prevent accidental fires and protect the metal, these metals are stored under oil.
(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
Answer:
Aluminium is highly reactive. It reacts with oxygen in the air and forms a non-reactive layer of aluminium oxide (Al₂O₃) on its surface. This protective layer prevents aluminium from reacting with air and other substances. Aluminium is also a good conductor of heat, and it is light and easy to shape. That is why we use it to make cooking utensils.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
Answer:
It is easier to obtain a metal from its oxide than from its sulphides and carbonates. So, before extraction, the metal sulphides and carbonates must be converted into metal oxides. The sulphide ores are converted into oxides by heating strongly in the presence of excess air. This process is known as roasting. The carbonate ores are changed into oxides by heating strongly in limited air. This process is known as calcination.
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.
Ans: The sour substances such as lemon or tamarind juice contain acids. These acids react with the coating of copper oxide or basic copper carbonate present on the surface of tarnished copper vessels. This removes the tarnish and makes the vessel shiny and reddish-brown again.
Q14. Differentiate between metals and non-metals on the basis of their chemical properties.
Answer:
| Metals | Non-metals |
|---|---|
| Metals are electropositive (and tend to lose electrons to form positive ions) | Non-metals are electronegative (and tend to gain electrons to form negative ions) |
| They react with oxygen to form basic oxides. | They react with oxygen to form acidic or neutral oxides. |
| They react with water to form oxides and hydroxides. Some metals react with cold water, some with hot water and some with steam. | Non-metals do not react with water. |
| They react with dilute acids to form salt and hydrogen gas. | They do not react with dilute acids and do not displace hydrogen. |
| More reactive metals can displace less reactive metals from their salt solutions. | Non-metals do not displace metals from salt solutions. |
| Metals act as reducing agents as they lose electrons. | Non-metals act as oxidising agents as they gain electrons. |
| They form ionic compounds. | They form covalent compounds. |
Q15. A man posed as a goldsmith and dipped a lady’s old gold bangles in a solution. The bangles sparkled like new, but their weight dropped drastically. Can you play the detective to find out the nature of the solution he used?
Answer:
The dishonest goldsmith used a solution called Aqua regia(Latin for “royal water”). Aqua regia is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. It is a highly corrosive and fuming liquid. Gold is a very unreactive metal, but aqua regia can dissolve gold.
When the bangles were dipped, the outer dull layer of gold dissolved into the solution, exposing the shiny inner layer. So the bangles looked new. But some gold had gone into the solution, and that is why their weight dropped.
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, so it does not corrode easily. On the other hand, Iron, the main metal in steel, reacts with steam and can cause corrosion. Copper is also a better conductor of heat than steel, so the water heats up faster. That is why copper is used to make hot water tanks instead of steel.