[3 Mark Question Answer]

Question 13 Marks

State one relevant observation for each of the following :
(i) A small piece of zinc is added to dilute hydrochloric acid.
(ii) Dilute hydrochloric acid is added to silver nitrate solution.
(iii) Hydrogen chloride gas fumes in moist air.

Answer

(i) The reaction starts with effervescence and evolution of a colourless gas hydrogen.
(ii) A curdy white precipitate of silver chloride is formed.
(iii) Hydrogen chloride gas dissolves in water vapour to from tiny droplets of hydrochloric acid.

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Question 23 Marks

State one relevant observation for each of the following :
(i) When dilute hydrochloric acid is added to sodium carbonate crystals.
(ii) Action of dilute hydrochloric acid on iron (II) sulphide.
(iii) Lead nitrate solution is mixed with dilute hydrochloric acid and heated.

Answer

(i) Lot of effervescence takes place with evolution of a colourless gas, i.e., carbon dioxide. The reaction mixture gets warm and crystals of sodium carbonate dissolve to form a colourless solution.
(ii) A foul smelling gas like rotten eggs is given off.
(iii) A thick white precipitate of lead chloride is formed.

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Question 33 Marks

(a) Name the acid used for the preparation of hydrogen chloride gas in the laboratory. Why is this particular acid preferred to other acids?
(b) For the preparation of hydrochloric acid in the laboratory :
(i) Why is direct absorption of hydrogen chloride gas in water not feasible?
(ii) What arrangement is done to dissolve hydrogen chloride gas in water?

Answer

(a) Conc. sulphuric acid.
Because it is non-volatile and has a high boiling point. So it displaces the volatile hydrogen chloride gas from the salt sodium chloride.
(b) (i) Because, if hydrogen chloride gas is directly absorbed in water, it leads to back suction and due to back suction the water enters the hot flask and breaks it.
(ii) An inverted funnel is attached to the delivery tube with the help of a rubber tubing. The rim of the funnel is placed in a beaker of water such that rim is 2 mm below the surface of water.

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Question 43 Marks

Write balanced chemical equations for the reaction of dilute hydrochloric acid with each of the following:
(i) iron (ii) sodium hydrogen carbonate (iii) iron(II) sulphide

Answer

(i) Fe(s) + 2HCl (aq) → FeCl₂(aq) + H₂(g)
(ii) NaHCO₃(s) + HCl(aq) → NaCl(aq) + H₂O(l) + CO₂(g)
(iii) FeS(s) + 2HCl(aq) → FeCl₂(aq) + H₂S(g)

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Question 53 Marks

What is aqua regia? How does it help in dissolving gold or platinum? Support your answer with chemical equations.

Answer

A mixture of 1 part (by weight) of conc. nitric acid and 3 parts (by weight) of conc. hydrochloric acid is called aqua regia.
Conc. HCl and conc. HNO₃ react to form nascent chlorine which reacts with gold or platinum to form their respective soluble chlorides.
HNO₃ + 3HCl (conc.) → 2H₂O + NOCI + 2(CI)
Au + 3(CI) → AuCl₃; Pt + 4(CI) → PtCl₄

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Question 63 Marks

(a) Hydrogen is burnt in a greenish-yellow gas A then another gas B is formed. The gas B gives dense white fumes with ammonia liquor. Name the gases A and B.
(b) Write chemical equations in support of your answer in (a).

Answer

(a) A is chlorine gas.
B is hydrogen chloride gas.
(b) H₂ + Cl₂ → 2HCl
NH₄OH + HCl → NH₄Cl + H₂O

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Question 73 Marks

How will you obtain the following from dil. HCl acid? Give equations.
(i) hydrogen (ii) carbon dioxide (iii) sulphur dioxide

Answer

(i) When zinc metal is treated with dilute HCl, it liberates hydrogen gas,
Zn + 2HCl (dil.) → ZnCl₂ + H₂
(ii) When sodium carbonate is treated with dilute HCl, it liberates carbon dioxide gas.
Na₂CO₃ + 2HCl (dil.) → 2NaCl + CO₂ + H₂O
(iii) When sodium sulphite is treated with dilute HCl, it liberates sulphur dioxide gas.
Na₂SO₃ + 2HCl (dil.) → 2NaCl + SO₂ + H₂O

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Question 83 Marks

Hydrogen chloride gas is prepared in the laboratory using concentrated sulphuric acid and sodium chloride. Answer the questions that follow based on this reaction :
(i) Give the balanced chemical equation for the reaction with suitable condition(s) if any.
(ii) Why is concentrated sulphuric acid used instead of concentrated nitric acid?
(iii) How is the gas collected?

Answer

(i) NaCl (s) $+ H _2 SO _4$ (aq) $\xrightarrow{<200^{\circ} C } NaHSO _4$ (aq) + HCl (g)
(ii) Conc. sulphuric acid is used since it is non-volatile and has a high boiling point. So it displaces the volatile hydrogen chloride from the salt sodium chloride.
(iii) Dry hydrogen chloride gas is collected by the upward displacement of air.

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Question 93 Marks

When concentrated hydrochloric acid is treated with potassium permanganate crystals a greenish yellow gas is given out.
(i) Name the gas evolved.
(ii) Write a fully balanced chemical equation for the reaction.
(iii) Is hydrochloric acid acting as oxidising agent or reducing agent?

Answer

(i) The gas evolved is chlorine gas.
(ii) 2KMnO₄ + 16HCl → 2KCl + 2MnCl₂ + 8H₂O + 5CI₂
(iii) Hydrochloric acid acts as a reducing agent.

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Question 103 Marks

In the laboratory preparation of hydrochloric acid, HCl gas is dissolved in water.
(a) Draw a diagram to show the arrangement used for the absorption of HCl in water.
(b) Why is such an arrangement necessary? Give two reasons.
(c) Write the chemical equations for the laboratory preparation of HCl gas when the reactants are:
(i) below 200° С (ii) above 200° С

Answer

(a)

(b) (i) It prevents the back suction of the gas
(ii) It helps in concentration of hydrochloric acid as it provides large surface area for the absorption of HCl gas
(c) (i) $NaCl + H _2 SO _4 \xrightarrow{<200^{\circ} C } NaHSO _4+ HCl$
(ii) $NaHSO _4+ NaCl \xrightarrow{>200^{\circ} C } Na _2 SO _4+ HCl$

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Question 113 Marks

To a solution of hydrogen chloride, the following substances are added separately in small portions. Copy and complete the table given below.

No.	Substance added	Gas evolved	Odour
(i)	Sodium sulphite	________	________
(ii)	Calcium carbonate	________	________
(iii)	Magnesium ribbon	________	________

Answer

No.	Substance added	Gas evolved	Odour
(i)	Sodium sulphite	Sulphur dioxide	Suffocating gas which causes coughing
(ii)	Calcium carbonate	Carbon dioxide	Faint acidic smell
(iii)	Magnesium ribbon	Hydrogen gas	Odourless

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Question 123 Marks

Give balanced chemical equation for the following :
(i) Sodium thiosulphate and dilute HCl.
(ii) Calcium hydrogen carbonate and dilute HCI.
(iii) Concentrated hydrochloric acid and potassium permanganate crystals.

Answer

(i) Na₂S₂O₃ + 2HCl → 2NaCl + H₂O + SO₂ + S
(ii) Ca(HCO₃)₂ + 2HCl → CaCl₂ + 2H₂O + 2CO₂
(iii) 2KMnO₄ + 16HCl(conc.) → 2KCl + 2MnCl₂ + 8H₂O + 5Cl₂

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Chemistry [3 Mark Question Answer]

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