Class 10 Science Chapter 3 Question Answers - Metals and Non-metals

Q1: Define the following terms
(i) Mineral
(ii) Ore
(iii) Gangue.
Ans:
(i) The inorganic elements or compounds which occur naturally in the earth’s crust are known as minerals.(ii) The minerals from which a metal can be profitably extracted are called ores.
(iii) The impurity of sand and rocky materials present in the ore is known as gangue.

Q2: 
(a) Due to which property of metals is metallic foils prepared?
(b) Write uses of aluminium foils.
Ans:
(a) Metallic foils are prepared, making use of the malleable property of metals.
(b) Aluminium foils are used for:
(i) Wrapping chocolates and foodstuff.
(ii) To prepare hydrogen.

Q3: Give reasons for the following
(i) Zinc oxide is considered an amphoteric oxide.
(ii) Non-metals in general do not displace hydrogen from dilute acids.
(iii) Metals conduct electricity.
Ans: 
(i) Zinc oxide is considered an amphoteric oxide because it shows both acidic and basic behaviour.
(ii) Non-metals do not react with dilute acids hence do not displace hydrogen from dilute acids.
(iii) That metals conduct electricity because they contain free electrons which can move easily through the metal and conduct electric current.

Q4: Explain the process of electrolytic refining of impure copper (Cu). Describe how this process helps in obtaining pure copper and write the balanced chemical equation for the electrolytic refining of impure copper.
Ans: Electrolytic refining is a process used to purify metals obtained from ore or other sources. In the case of impure copper, this process involves the use of electrolysis to remove impurities and obtain pure copper.Process of Electrolytic Refining: Impure copper is used as the anode, while a thin sheet of pure copper serves as the cathode. Both are immersed in an electrolyte solution containing copper sulfate (CuSO₄) and sulfuric acid (H₂SO₄). When electric current passes through the electrolyte, copper from the anode dissolves into the solution as copper ions (Cu²⁺) and moves towards the cathode. At the cathode, copper ions are reduced and deposited as pure copper.
Balanced Chemical Equation for Electrolytic Refining of Copper:

• At Anode: Cu → Cu²⁺ + 2e⁻
• At Cathode: Cu²⁺ + 2e⁻ → Cu

The overall process ensures that impurities from the anode settle at the bottom as anode mud or dissolve into the electrolyte. The pure copper deposited at the cathode is collected, resulting in the purification of copper.

Q8: What property of hydrogen is observed in the following experiments?
(i) Pop sound is heard when a burning splint is introduced at the mouth of hydrogen-filled jar.
(iii) When black cupric oxide is heated in a stream of hydrogen, reddish colour is obtained.
Ans:
(i) Pop sound is due to the combustible property of hydrogen. Hydrogen burns with oxygen at the mouth of the hydrogen filled jar.
(iii) When black cupric oxide (CuO) is heated in a stream of hydrogen, it undergoes a reduction reaction. The hydrogen acts as a reducing agent and reduces the copper(II) oxide to metallic copper, which has a reddish color:
Q9: Write chemical equations for reactions taking place when
(i) Cinnabar is heated in air.
(ii) Concentrated sulphuric acid and sulphur are heated together. Calcium metal reacts with water.
Ans:
(i) Cinnabar is heated in air
2HgS + 3O₂ (g) → 2HgO (s) +2SO₂
(ii) Calcium metal reacts with water.
Ca(s) + 2H₂O(I) → Ca(OH)₂(aq) + H₂(g).

Q10: Why do some metals like Na, K, Ca, Mg not occur in nature as free elements?
Ans: Metals like Na, K, etc (alkali metals) and Ca, Mg, etc (alkaline earth metals) are very reactive and hence they react with atmospheric oxygen and carbon dioxide and also with other non-metals like sulphur present in the earth’s crust to form compounds like oxides, carbonates, sulphides, sulphates and chlorides. So they do not occur in a free state but are found in the form of the above compounds.

Q12: Explain the term "amphoteric oxides" and provide examples. Describe the reaction of an amphoteric oxide with an acid and a base. Write the balanced chemical equation for the reaction of aluminum oxide (Al₂O₃) with sodium hydroxide (NaOH).
Ans: Amphoteric oxides are oxides that can exhibit both acidic and basic properties. They can react with both acids and bases to form salts and water.Examples of Amphoteric Oxides: Aluminum oxide (Al₂O₃) and zinc oxide (ZnO) are examples of amphoteric oxides.
Reaction with Acid: Amphoteric oxides react with acids to form salts and water. For example, aluminum oxide reacts with hydrochloric acid to produce aluminum chloride and water.
Balanced Chemical Equation for Reaction with Acid:
Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O
Reaction with Base:
Amphoteric oxides also react with bases to form salts and water. For instance, aluminum oxide reacts with sodium hydroxide to produce sodium aluminate and water.
Balanced Chemical Equation for Reaction with Base:
Al₂O₃ + 2NaOH → 2NaAlO₂ + 2H₂O

Q17: Describe an activity to find out the conditions under which iron rusts.

Ans:  Procedure:
(i) Take three test tubes and put clean nails in each of the three tubes. Label them as A, B and C.
(ii) Pour some water in test tube A and cork it.
(iii) In tube B, pour some boiled distilled water along with some turpentine oil and cork it.
(iv) In test tube C, add some anhydrous calcium chloride and cork it.
(v) Look these test tubes properly and keep them undisturbed for a few day

Observation: Only in test tube A, iron nails get rusted since the nails in this test tube are exposed to both air and water.
Conclusion: Both air and water are required for rusting of iron.

Q18: (a) Define corrosion.
(b) What is corrosion of iron called?
(c) How will you recognise the corrosion of silver?
(d) Why corrosion of iron is a serious problem?
(e) How can we prevent corrosion of iron? 

Ans:(a) The process of slowly eating up of metals due to their conversion into oxides, carbonates, sulphides, etc., by the action of atmospheric gases and moisture is called corrosion.
(b) The corrosion of iron is called rusting.
(c) Silver articles become black after sometime when exposed to air. This is due to formation of a coating of black silver sulphide (Ag₂S) on its surface by the action of H₂S gas present in the air.
(d) Corrosion of iron is a serious problem. Every year large amount of money is spent to replace damaged iron articles. Corrosion causes damage to car bodies, bridges and iron railings, ships and to all objects made of metals specially those of iron.
(e) Corrosion of iron is prevented by coating it with a layer of oil. The reason being that the layer of oil does not allow air and water to react the surface of iron. Corrosion of iron can also be prevented by painting, greasing, galvanising, anodising, electroplating or making alloys.

Q19: An ore on treatment with dilute hydrochloric acid produces brisk effervescence. Name the type of ore with one example. What steps will be required to obtain metal from the enriched ore? Also write the chemical equations for the reactions involved in the process.

Ans: The ore on treatment with dilute hydrochloric acid produces brisk effervescence hence, it must be a carbonate ore. Calamine (ZnCO₃) is an important carbonate ore of zinc.
Steps required to obtain metal from the enriched carbonate Are:
(a) Conversion of the carbonate ore into metal oxide : This is done by calcination (for carbonate ores).
Calcination is the process of heating the ore strongly in the absence or limited supply of air. The zinc carbonate on heating decomposes to form zinc oxide as shown :

(b) Reduction of the metal oxide to metal: As zinc is moderately reactive, zinc oxide cannot be reduced by heating alone. Hence, it is reduced to zinc by using a reducing agent such as carbon.

Q20: (i) Write down the electronic configuration
of magnesium and oxygen.
(ii) Give two general properties of the compound formed by combination of magnesium and oxygen.
(iii) Show the formation of this compound by the transfer of electrons.

Ans: (i) Atomic number of magnesium (Mg) = 12
∴ Its electronic configuration = 2, 8, 2
Atomic number of oxygen = 8
Electronic configuration of oxygen = 2, 6

(ii) Magnesium (Mg) reacts with oxygen (O₂) to form magnesium oxide (MgO).
2Mg + O₂ → 2MgO
Properties of MgO are :
(a) It involves ionic bonding.
(b) It has high melting point due to strong electrostatic forces of attraction between Mg²⁺ and O^2- ions.

(iii) In the formation of magnesium oxide, two electrons are transferred from magnesium atom to oxygen atom as represented :