A non-metal A, which is the largest constituent of air, reacts with hydrogen in a 1:3 ratio in the presence of a catalyst to form a gas B. On heating B with oxygen, it produces an oxide C. When this oxide is passed into water in the presence of air, it produces an acid D that acts as a strong oxidising agent. Identify A, B, C and D, and state the group of the periodic table to which A belongs.
Identification:
A — Nitrogen (\(N_2\))
B — Ammonia (\(NH_3\))
C — Nitric oxide (\(NO\))
D — Nitric acid (\(HNO_3\))
Stepwise reactions:
Formation of ammonia:
\[ N_2 + 3H_2 \rightarrow 2NH_3 \]
Formation of nitric oxide:
\[ 4NH_3 + 5O_2 \xrightarrow{heat} 4NO + 6H_2O \]
Formation of nitric acid:
\[ 2NO + O_2 \rightarrow 2NO_2 \]
\[ 4NO_2 + 2H_2O + O_2 \rightarrow 4HNO_3 \]
Group of A: Nitrogen belongs to Group 15.
Describe the steps involved in the extraction of metals of low and medium reactivity from their respective sulphide ores.
Extraction from sulphide ore of low reactivity metals:
Roasting:
The sulphide ore is heated in the presence of air to convert it into oxide.
\[ 2MS + 3O_2 \rightarrow 2MO + 2SO_2 \]
Reduction:
The metal oxide is reduced to metal.
\[ MO + C \rightarrow M + CO \]
Refining:
The crude metal obtained is purified.
Extraction from sulphide ore of medium reactivity metals:
Roasting:
Ore is heated in excess air to remove sulphur.
Reduction:
The oxide formed after roasting is reduced to metal.
Refining:
The metal obtained is purified by electrolytic or other methods.
Explain each of the following:
Reactivity of aluminium decreases if it is dipped in \(HNO_3\).
Carbon cannot reduce the oxides of sodium or magnesium.
Sodium chloride does not conduct electricity in the solid state, but conducts in aqueous or molten state.
Iron articles are galvanised.
Metals like Na, K, Ca and Mg are never found in free state.
Aluminium in \(HNO_3\):
Aluminium reacts with nitric acid to form a protective oxide layer of \(Al_2O_3\), preventing further reaction. This decreases its reactivity.
Carbon cannot reduce Na or Mg oxides:
Metals like Na and Mg are more reactive than carbon. Their oxides are very stable, so carbon cannot reduce them.
Conductivity of NaCl:
In solid NaCl, ions are fixed in a rigid lattice and cannot move, so electricity is not conducted. In molten or aqueous NaCl, ions can move freely, enabling conduction.
Galvanisation:
Iron is galvanised by coating with zinc to prevent corrosion and rusting.
Highly reactive metals:
Na, K, Ca and Mg react quickly with air, water or other elements and therefore occur only as compounds in nature.
Given below are the steps involved in the extraction of copper from its ore. Write the reactions involved and draw a labelled diagram for electrolytic refining of copper.
(a) Roasting of copper(I) sulphide
(b) Reduction of copper(I) oxide with copper(I) sulphide
(c) Electrolytic refining
(a) Roasting of copper(I) sulphide:
\[ 2Cu_2S(s) + 3O_2(g) \xrightarrow{heat} 2Cu_2O(s) + 2SO_2(g) \]
(b) Reduction of copper(I) oxide with copper(I) sulphide:
\[ 2Cu_2O + Cu_2S \xrightarrow{heat} 6Cu + SO_2 \]
This is known as auto-reduction.
(c) Electrolytic refining:
At cathode:
\[ Cu^{2+}(aq) + 2e^- \rightarrow Cu(s) \]
At anode:
\[ Cu(s) \rightarrow Cu^{2+}(aq) + 2e^- \]
Diagram:
(A labelled diagram showing anode, cathode, electrolyte (acidified copper sulphate), and impurities such as anode mud.)
Three metals X, Y and Z react differently with water. X reacts with cold water, Y with hot water, and Z with steam only. Identify X, Y and Z and arrange them in order of increasing reactivity.
Identification:
X — Sodium, Potassium (alkali metals)
Y — Magnesium or Calcium (alkaline earth metals)
Z — Iron
Order of increasing reactivity:
\[ Fe < Mg < Na \]
Alkali metals react most vigorously with water, alkaline earth metals react moderately, and iron reacts only with steam.
An element A burns with a golden flame in air. It reacts with another element B (atomic number 17) to give product C. An aqueous solution of C on electrolysis gives a compound D and liberates hydrogen. Identify A, B, C and D, and write all reactions involved.
Identification:
A — Sodium (Na)
B — Chlorine (\(Cl_2\))
C — Sodium chloride (\(NaCl\))
D — Sodium hydroxide (\(NaOH\))
Reactions involved:
Formation of sodium chloride:
\[ 2Na + Cl_2 \rightarrow 2NaCl \]
Electrolysis of aqueous sodium chloride:
\[ 2NaCl(aq) + 2H_2O(l) \rightarrow 2NaOH(aq) + Cl_2(g) + H_2(g) \]
Two ores A and B were taken. On heating, ore A gives \(CO_2\), whereas ore B gives \(SO_2\). What steps will you take to convert both ores into metals?
Since ore A gives \(CO_2\), it is a carbonate ore (\(MCO_3\)).
Step 1: Calcination:
\[ MCO_3 \xrightarrow{heat} MO + CO_2 \]
Step 2: Reduction:
\[ MO + C \rightarrow M + CO \]
Since ore B gives \(SO_2\), it is a sulphide ore (\(MS\)).
Step 1: Roasting:
\[ 2MS + 3O_2 \rightarrow 2MO + 2SO_2 \]
Step 2: Reduction:
\[ MO + C \rightarrow M + CO \]