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Science Answer the questions.[Che-3M]

Metals and Non-Metals · CBSE STD 10 (CBSE - English Medium). 15 questions.

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Answer the questions.[Che-3M]

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15 questions · timed · auto-graded

Question 13 Marks
Why should the metal sulphides and carbonates be converted to metal oxides in the process of extraction of metal from them?
Answer

It is quite easy to obtain a metal from metal oxide by carrying its reduction with a suitable reducing agent. However, metal sulphides and carbonates are converted to the oxide form and then reduced.

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Question 23 Marks
When a metal X is treated with cold water, it gives a basic salt Y with molecular formula XOH (Molecular mass = 40) and liberates a gas Z which easily catches fire. Identify X, Y and Z and also write the reaction involved.
Answer
The atomic mass of metal X = 56 – Mass of OH group = 56 — 17 = 39u. This shows that the metal ‘X’ is potassium (K) and the basic salt ‘Y’ is potassium hydroxide (KOH). It is formed by reacting potassium with cold water. Hydrogen gas ‘Z’ evolved in the reaction catches fire.
2K(s) + 2H2O(aq) → 2KOH(aq) + H2(g)
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Question 33 Marks
Two ores A and B were taken. On heating ore A gives CO2 whereas, ore B gives SO2. What steps will you take to convert them into metals?
Answer
Since the ore ‘A’ of the metal gives CO2 upon heating, it is some metal carbonate (MCO3). It can be converted to the metallic form as follows:

Calcination:

$\text{MCO}_3\text{(s)}\xrightarrow{\text{heat}}\text{MO(s)}+\text{CO}_2\text{(g)}$

Smelting:

$\text{MO}\text{(s)} +\text{C(s)}\xrightarrow{\text{heat}}\text{M(s)}+\text{CO}\text{(g)}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{(coke)}$

Since the ore ‘Y’ of the metal gives SO2 upon heating, it can be some metal sulphide (MS). It can be converted to the metallic form as follows:

Roasting:

$2\text{MS}\text{(s)}+3\text{O}_2\text{(g)}\rightarrow2\text{MO(s)}+2\text{SO}_2\text{(g)}$

Reduction:

$\text{MO}\text{(s)}+\text{C}\text{(s)}\rightarrow\text{M(s)}+\text{CO}\text{(g)}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{(coke)}$

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Question 43 Marks
Of the three metals X, Y and Z. X reacts with cold water, Y with hot water and Z with steam only. Identify X, Y and Z and also arrange them in order of increasing reactivity.
Answer
X is sodium, Y is magnesium and Z is iron.
2Na + 2H2O → 2NaOH + H2
Mg + 2H2O → Mg(OH)2 + H2
3Fe + 4H2O → Fe3O4 + 4H2
Their sequence in reactivity series is as follows:
Fe < Mg < Na.
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Question 53 Marks
Iqbal treated a lustrous, divalent element M with sodium hydroxide. He observed the formation of bubbles in reaction mixture. He made the same observations when this element was treated with hydrochloric acid. Suggest how can he identify the produced gas. Write chemical equations for both the reactions.
Answer
The divalent element M is a metal. It reacts with both sodium hydroxide (alkali) and dilute hydrochloric acid to evolve hydrogen gas.
M(s) + 2NaOH(aq) → Na2MO2(aq) + H2(g)
M(s) + 2HCl(aq) → MCl2(aq) + H2(g)
The gas burns with a pop sound when a burning match stick is brought near it.
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Question 63 Marks
Generally, when metals are treated with mineral acids, hydrogen gas is liberated but when metals (except Mn and Mg), treated with HNO3, hydrogen is not liberated, why?
Answer
It is because HNO3 is an oxidising agent and it gets reduced to NO if it is dilute and NO2 if HNOs is concentrated, it oxidises H2 to H2O.
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Question 73 Marks
During extraction of metals, electolytic refining is used to obtain pure metals.
  1. Which material will be used as anode and cathode for refining of silver metal by this process?
  2. Suggest a suitable electrolyte also.
  3. In this electrolytic cell, where do we get pure silver after passing electric current?
Answer
  1. Pure silver rod will be used as cathode and impure silver rod will be used as anode.
  2. Ag NO3 (aq) can be used as electrolyte.
  3. Pure silver will be formed at cathode.

At anode: Ag → Ag++ e-

At cathode: Ag++ e- → Ag

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Question 83 Marks
Compound X and aluminium are used to join railway tracks.
  1. Identify the compound X.
  2. Name the reaction.
  3. Write down its reaction.
Answer
Railway trakcs as we all know, are made up of iron. This means that the compound A is an oxide of iron (Fe2CO3). It is reduced by aluminium by thermit reaction with aluminium.
Fe2O3(s) + 2Al(s) → Al2O3(s) + 2Fe(s) + heat.
The reaction is highly exothermic and as a result, iron is in molten state and can weld the broken railway tracks. The process is also called aluminothermie reduction or thermit process.
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Question 93 Marks
A solution of CuSO4 was kept in an iron pot. After few days the iron pot was found to have a number of holes in it. Explain the reason in terms of reactivity. Write the equation of the reaction involved.
Answer
Iron is more reactive than copper. Due to this, iron displaced copper from copper sulphate to form iron sulphate. A portion of the iron pot got dissolved in this process and caused holes in it. Following equation is involved in this reaction.
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
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Question 103 Marks
A non-metal X exists in two different forms Y and Z. Y is the hardest natural substance, whereas Z is a good conductor of electricity. Identify X, Y and Z.
Answer

‘X’ is carbon ‘Y’ is diamond ‘Z’ is graphite.

‘Y’ (diamond) is hardest natural substance.

‘Z’ (graphite) is good conductor of electricity.

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Question 113 Marks
A non-metal A is an important constituent of our food and forms two oxides B and C. Oxide B is toxic whereas C causes global warming.
  1. Identify A, B and C.
  2. To which Group of Periodic Table does A belong?
Answer

The non-metal A is carbon. It is an important constituent of our food in different forms. For example, glucose (C6H12O6) contains carbon. In fact, all food materials are organic compounds and these contain carbon as essential constituent. The two oxides of carbon are, carbon monoxide (B) and carbon dioxide (C). Carbon dioxide causes global warming.

  1. A = Carbon (C),

B = Carbon monoxide (CO),

C = Carbon dioxide (CO2)

  1. Carbon is the first member of group 14 in the Long form of Periodic Table.
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Question 123 Marks
An element A reacts with water to form a compound B which is used in white washing. The compound B on heating forms an oxide C which on treatment with water gives back B. Identify A, B and C and give the reactions involved.
Answer
Since the compound ‘B’ is used for white wash, it is calcium hydroxide and the element ‘A’ is calcium. Upon heating ‘B’ forms calcium oxide ‘C’. It reacts with water to give calcium hydroxide ‘B’ again.

$\text{Ca(s) + 2H}_2\text{O(aq)}\rightarrow\text{Ca(OH)}_2\text{(s) + H}_2\text{(g)}\\ \ \ \text{(A)}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{(B)}$

$\text{Ca(OH)}_2\text{(s)}\xrightarrow{\text{heat}}\text{CaO(s) + H}_2\text{O(g)}\\\ \ \text{(B})$

$\text{CaO(s) + H}_2\text{O(aq)}\rightarrow\text{Ca(OH)}_2\text{(s)}$

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Question 133 Marks
An element A burns with golden flame in air. It reacts with another element B, atomic number 17 to give a product C. An aqueous solution of product C on electrolysis gives a compound D and liberates hydrogen. Identify A, B, C and D. Also write down the equations for the reactions involved.
Answer
Element ‘A’ that burns with golden flame is sodium (Na). Element ‘B’ with atomic number 17 is chlorine (Cl). 
Sodium and chlorine react to form sodium chloride (NaCl) which is an ionic compound.

2Na(s) + Cl2(g) → 2NaCl(s)

The aqueous solution of sodium chloride, also called as brine when goes through electrolysis, forms sodium hydroxide (NaOH), hydrogen and chlorine gas.

$2\text{NaCl(aq) + 2H}_2\text{O(l)}\xrightarrow{\text{Electrolysis}}2\text{NaOH(aq) + Cl}_2+\text{H}_2\text{(g)}$

Hence, A = Sodium (Na), B = Chlorine (Cl), C = Sodium chloride (NaCl), D = Sodium hydroxide (NaOH).

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Question 143 Marks
A metal that exists as a liquid at room temperature is obtained by heating its sulphide in the presence of air. Identify the metal and its ore and give the reaction involved.
Answer
This metal is mercury because mercury exists as liquid at room temperature. Mercury ore is called cinnabar (HgS). When cinnabar is heated in presence of air, following reaction takes place:
2Hgs + 3O2 → 2HgO + 2SO2
Mercury oxide is further heated to obtain mercury:
2HgO → 2Hg + O2
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Question 153 Marks
A metal A, which is used in thermite process, when heated with oxygen gives an oxide B, which is amphoteric in nature. Identify A and B. Write down the reactions of oxide B with HCl and NaOH.
Answer
Aluminium (Al) is used in thermite process so metal A is Aluminium. The reaction of Al with oxygen forms aluminium oxide Al2O3 which is amphoteric in nature as it can exhibit acidic as well as basic nature.
4Al(s) + 3O2(g) → 2Al2O3(s)
Hence, A = Aluminium and B = Aluminium oxide
Reactions of aluminium oxide with HCl and NaOH are as given below;
Al2O3(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2O(l)
Al2O3(s) + 2NaOH(aq) → 2NaAlO2(aq) + H2O(l)
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