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Study of Compounds — Hydrogen Chloride

Solutions for Chemistry, Class 10, ICSE

Exercise 8 Long Answer Type

13 questions

Question 1

Draw a labelled diagram for the laboratory preparation of hydrogen chloride gas and answer the following.

(a) Name the acid used. Why is this particular acid preferred to other acids?

(b) Give the balanced equation for the reaction.

(d) Phosphorus pentoxide and calcium oxide are good drying agents, but they cannot be used to dry hydrogen chloride gas. Why?

(e) Why is direct absorption of HCl gas in water not feasible?

(f) What arrangement is done to dissolve HCl gas in water.

Exercise 8 Long Answer Type

Answer:

The labelled diagram for the laboratory preparation of hydrogen chloride gas is shown below:

Draw a labelled diagram for the laboratory preparation of hydrogen chloride gas. Hydrogen Chloride, Concise Chemistry Solutions ICSE Class 10

(a) Conc. H₂SO₄ is used for the preparation of hydrogen chloride gas in the laboratory.

As conc. H₂SO₄ is non-volatile and has a high boiling point, therefore, it displaces the volatile hydrogen chloride from the salt sodium chloride. Hence, conc. H₂SO₄ is used as a reactant in the laboratory preparation of HCl from sodium chloride.

(b) $\text{NaCl} + \text{H}_2\text{SO}_4 \xrightarrow{\lt 200 \degree\text{C}} \text{NaHSO}_4 + \text{HCl [g.]}$

Reason — Drying agent used for drying should only remove the moisture and not react with it, hence, conc. sulphuric acid is used as the drying agent.

(d) Phosphorus pentoxide and calcium oxide are good drying agents, but they cannot be used to dry hydrogen chloride gas since they react with it.

2P₂O₅ + 3HCl ⟶ POCl₃ + 3HPO₃

CaO + 2HCl ⟶ CaCl₂ + H₂O

(e) Direct absorption of hydrogen chloride gas in water is not feasible because it causes back suction in the delivery tube.

Hydrogen chloride gas is extremely soluble in water.
If a delivery tube through which HCl gas is passed is directly immersed in water, the rate of absorption of HCl gas is high and hence a partial vacuum is created in the tube.
The pressure outside being higher causes the water to be pushed up into the delivery tube and damages the apparatus. This is called back-suction.

(f) A special funnel arrangement is used to dissolve HCl gas in water as it provides a large surface area for absorption while preventing back-suction. The rim of the funnel is positioned so that it just touches the water in the trough. If back-suction occurs, the water rises up the funnel and the air gap between the rim of the funnel and the water's surface equalizes the pressure inside and outside.

Question 2

The given set up in the figure is for the preparation of an acid

(a) Name the acid prepared by this method.

(b) Name the reactants used.

(d) What is the drying agent used? Why is this drying agent chosen ?

(e) What is the role of inverted funnel in the arrangement?

Exercise 8 Long Answer Type

Answer:

(a) Hydrochloric acid (HCl)

(b) The reactants used are sodium chloride and sulphuric acid.

(c) The empty flask acts as an Anti-Suction device. If back suction takes place then the water gets collected in it and will not reach the generating flask.

(d) The drying agent used is Concentrated Sulphuric acid. It is chosen as drying agent because it does not react with HCl.

(e) The role of the inverted funnel in the arrangement is -

It prevents or minimizes back suction of water.
It provides a large surface area for absorption of HCl gas.

Question 3

How will you prove that Hydrochloric acid contains

(i) hydrogen

(ii) chlorine.

Write equations for the reactions.

Exercise 8 Long Answer Type

Answer:

(i) Using an active metal below magnesium

Fe + 2HCl ⟶ FeCl₂ + H₂↑

(ii) Using an oxidising agent not containing lead.

MnO₂ + 4HCl ⟶ MnCl₂ + 2H₂O + Cl₂↑

Question 4

Give three distinct tests [apart from using an indicator] you would carry out with solution of HCl to illustrate the typical properties of an acid.

Exercise 8 Long Answer Type

Answer:

(i) Action on metals — Hydrochloric acid reacts with metals above hydrogen in the activity series forming metallic chlorides and evolving hydrogen.

Ca + 2HCl ⟶ CaCl₂ + H₂ ↑

(ii) Action on oxides — Hydrochloric acid reacts with oxides to form salt and water only.

CuO + 2HCl ⟶ CuCl₂ + H₂O

(iii) With salts of weaker acids — Hydrochloric acid decomposes salts of weaker acids.

Na₂CO₃ + 2HCl ⟶ 2NaCl + H₂O + CO₂ ↑

Question 5

Convert:

(a) Two soluble metallic nitrates to insoluble metallic chlorides using dil. HCl.

(b) Insoluble iron(II) oxide to a soluble compound.

(d) Metal sulphide to an offensive smelling gas.

Exercise 8 Long Answer Type

Answer:

(a) Pb(NO₃)₂ + 2HCl ⟶ PbCl₂ + 2HNO₃
Hg₂(NO₃)₂ + 2HCl ⟶ Hg₂Cl₂ + 2HNO₃

(b) FeO + 2HCl ⟶ FeCl₂ + H₂O

(d) Na₂S + 2HCl ⟶ 2NaCl + H₂S ↑

Question 6

Study the flow chart and give balanced equations with conditions for the conversions A, B, C, D and E

Exercise 8 Long Answer Type

Answer:

The balanced chemical reactions are:

A : $\text{NaCl} + \text{H}_2\text{SO}_4 \xrightarrow{\lt 200 \degree\text{C}} \text{NaHSO}_4 + \text{HCl [g]}$ ↑

B : $\text{Zn} + 2\text{HCl ( dil.)} \xrightarrow{\Delta} \text{ZnCl}_2 + \text{H}_2$ ↑

C : AgNO₃ + HCl ⟶ AgCl (white ppt.) + HNO₃

D : $\text{MnO}_2 + \underset{\text{Conc.}}{\text{4HCl}} \xrightarrow{\Delta} \text{MnCl}_2 + 2\text{H}_2\text{O} + \text{Cl}_2$ ↑

E : NaHCO₃ + HCl ⟶ NaCl + H₂O + CO₂ ↑

Question 7

In the laboratory preparation of hydrochloric acid, hydrogen chloride gas is dissolved in water.

(a) Draw a diagram to show the arrangement used for the absorption of HCl gas in water.

(b) State why such an arrangement is necessary. Give two reasons for the same.

(A) below 200°C

(B) above 200°C

Exercise 8 Long Answer Type

Answer:

(a) Below diagrams show the special funnel arrangement used for the absorption of HCl gas in water:

Draw a diagram to show the arrangement used for the absorption of HCl gas in water. Study of Hydrogen Chloride, Simplified Chemistry Dalal Solutions ICSE Class 10.

(b) The reasons are :

Prevents or minimizes back-suction of water.
Provides a large surface area for the absorption of the HCl gas.

(A) $\text{NaCl} + \text{H}_2\text{SO}_4 \xrightarrow{\lt 200 \degree\text{C}} \text{NaHSO}_4 + \text{HCl [g]}$ ↑

(B) $\text{2NaCl} + \text{H}_2\text{SO}_4 \xrightarrow{\gt 200 \degree\text{C}} \text{Na}_2\text{SO}_4 + \text{2HCl [g}]$ ↑

Question 8

Study the figure given below and answer the questions that follow :

Study the figure and answer the questions. Identify the gas Y. What property of gas Y does this experiment demonstrate? Name another gas which has the same property and can be demonstrated through this experiment. Study of Hydrogen Chloride, Simplified Chemistry Dalal Solutions ICSE Class 10.

(i) Identify the gas Y.

(ii) What property of gas Y does this experiment demonstrate?

(iii) Name another gas which has the same property and can be demonstrated through this experiment.

Exercise 8 Long Answer Type

Answer:

(i) Dry HCl (Hydrogen chloride) gas is the gas Y

(ii) High solubility of HCl in water

(iii) Ammonia (NH₃) gas also demonstrates high solubility in water.

Question 9

Refer to the diagram given below and write balanced equations with conditions, if any, for the following conversions P to S.

Exercise 8 Long Answer Type

Answer:

P — $\text{NaCl} + \text{H}_2\text{SO}_4 \xrightarrow{\lt 200 \degree\text{C}} \text{NaHSO}_4 + \text{HCl [g]}$ ↑

Q — Fe + 2HCl (dil.) ⟶ FeCl₂ + H₂ [g]

R — NH₄OH + HCl (dil.)⟶ NH₄Cl + H₂O

S — $\text{PbO}_2 + 4\text{HCl} \xrightarrow{\Delta} \text{PbCl}_2 + 2\text{H}_2\text{O} + \text{Cl}_2$ ↑

Question 10

State your observations:

(a) HCl gas is passed through lead nitrate solution and the mixture is heated.

(b) Hydrochloric acid is added to silver nitrate solution.

Exercise 8 Long Answer Type

Answer:

(a) When HCl gas is passed through lead nitrate, white precipitate of lead chloride is formed.

Pb(NO₃)₂ + 2HCl ⟶ PbCl₂ ↓ + 2HNO₃

(b) Hydrochloric acid, when reacted with silver nitrate solution it gives a thick curdy white precipitate of silver chloride. This white precipitate is insoluble in nitric acid.

AgNO₃ + HCl ⟶ AgCl ↓ + HNO₃

(c) On addition of ammonium hydroxide, the resultant of part (b) i.e., thick curdy white precipitate of silver chloride dissolves and forms a complex salt called diammine silver (I) chloride.

AgCl + 2NH₄OH ⟶ [Ag(NH₃)₂Cl)] + 2H₂O

Question 11

Distinguish by using HCl.

(a) Lead nitrate solution and silver nitrate solution.

(b) Potassium sulphite and potassium sulphide.

Exercise 8 Long Answer Type

Answer:

(a) On reaction with HCl, lead nitrate solution gives white precipitate which can be dissolved in hot water.

Pb(NO₃)₂ + 2HCl ⟶ PbCl₂ ↓ + 2HNO₃

Whereas, silver nitrate solution gives thick curdy white precipitate which is insoluble in hot water.

AgNO₃ + HCl ⟶ AgCl ↓ + HNO₃

(b) On reaction with HCl, potassium sulphite gives SO₂ gas with pungent odour

K₂SO₃ + 2HCl ⟶ 2KCl + H₂O + SO₂ ↑

However, potassium sulphide gives H₂S gas with rotten eggs odour.

K₂S + 2HCl ⟶ 2KCl + H₂S ↑

Question 12

The following questions pertain to the laboratory preparation of hydrogen chloride gas:

(a) Write the equation for it's preparation mentioning the conditions required.

(b) Name the drying agent used in the above preparation and give a reason for the choice.

Exercise 8 Long Answer Type

Answer:

(a) The equation for the laboratory preparation of hydrogen chloride gas :

$\text{NaCl} + \text{H}_2\text{SO}_4 \xrightarrow{\lt 200 \degree\text{C}} \text{NaHSO}_4 + \text{HCl [g]}$ ↑

(b) Concentrated sulphuric acid is used as the drying agent used in the above preparation.

Reason — Drying agent used for drying should only remove the moisture and not react with it, hence, conc. sulphuric acid is used as the drying agent. Other drying agents like phosphorous pentoxide (P₂O₅) and quick lime (CaO) cannot be used since they react with hydrogen chloride gas.

(c) Temperature is maintained at nearly 200°C as at higher temperatures above 200°C the glass apparatus may crack, fuel is wasted, sodium sulphate formed, forms a hard crust which sticks to the glass and is difficult to remove.

Question 13

Identify the gas evolved and give the chemical test in each of the following cases.

Dilute hydrochloric acid reacts with:

(i) Iron [II] sulphide.

(ii) Sodium sulphite.

Exercise 8 Long Answer Type

Answer:

(i) H₂S gas is evolved when dilute hydrochloric acid reacts with Iron [II] sulphide.

FeS + 2HCl ⟶ FeCl₂ + H₂S ↑

(ii) SO₂ is evolved when dilute hydrochloric acid reacts with sodium sulphite.

Na₂SO₃ + 2HCl ⟶ 2NaCl + H₂O + SO₂ [g] ↑

Exercise 8 Multiple Choice Type

11 questions

Question 1

Hydrogen chloride molecule is:

Polar covalent
Non polar
Ionic
Co-ordinate

Exercise 8 Multiple Choice Type

Answer:

Polar covalent

Reason — Hydrogen chloride (HCl) is a polar covalent molecule because it is formed by sharing of electrons between hydrogen and chlorine atoms. However, chlorine is more electronegative than hydrogen, so it pulls the shared electrons closer to itself. This creates a partial negative charge on chlorine and a partial positive charge on hydrogen, making the molecule polar.

Question 2

Hydrogen chloride gas being highly soluble in water is dried by

Anhydrous calcium chloride
Phosphorous pentoxide
Quicklime
Conc. sulphuric acid

Exercise 8 Multiple Choice Type

Answer:

Conc. sulphuric acid.

Reason — Drying agent used for drying should only remove the moisture and not react with it, hence, conc. sulphuric acid is used as the drying agent.

Question 3

The aim of the Fountain experiment is to prove that:

HCl turns blue litmus red
HCl is denser than air
HCl is highly soluble in water
HCl fumes in moist air

Exercise 8 Multiple Choice Type

Answer:

HCl is highly soluble in water

Reason — Fountain experiment is performed to show the great solubility of HCl gas in water.

Question 4

HCl dissolves in toluene (C₆H₅CH₃) and the solution:

P — contains hydronium ions.

Q — can produce carbon dioxide on reacting with sodium carbonate.

R — does not show any acidic property.

Which of the following holds true?

Only P
Only Q
Only R
Both P and Q

Exercise 8 Multiple Choice Type

Answer:

Only R

Reason — Toluene is an organic solvent and non-polar in nature. When HCl dissolves in toluene, it does not ionize to form hydronium [H₃O⁺] ions. Since there are no free hydrogen ions, the solution does not show acidic properties and also cannot react with sodium carbonate to release carbon dioxide gas. Therefore, only R is correct — the solution does not show any acidic property. b

Question 5

Assertion (A): HCl is produced by the reaction of hydrogen and chlorine in diffused sunlight.

Reason (R): This reaction is explosive in sunlight.

Both A and R are true and R is the correct explanation of A.
Both A and R are true but R is not the correct explanation of A.
A is true but R is false.
A is false but R is true.

Exercise 8 Multiple Choice Type

Answer:

Both A and R are true and R is the correct explanation of A.

Explanation— HCl is produced, when moist hydrogen gas combines with chlorine in presence of diffused sunlight. Hence, assertion (A) is true.

${\text{H}_2} + {\text{Cl}_2} \xrightarrow[\text{sunlight}]{\text{diffused}} {2\text{HCl}}$

The formation HCl is a explosive reaction in direct sunlight but it is negligible in dark. So, it is carried out in diffused sunlight. Hence, reason (R) is true.

Therefore, Reason (R) thus provides a valid explanation for why this reaction is occurring in diffused sunlight. Hence, Reason (R) is the correct explanation of assertion

Question 6

Assertion (A): The Fountain experiment is used to demonstrate the high solubility of HCl gas.

Reason (R): Red litmus solution turns blue in Fountain experiment.

Both A and R are true and R is the correct explanation of A.
Both A and R are true but R is not the correct explanation of A.
A is true but R is false.
A is false but R is true.

Exercise 8 Multiple Choice Type

Answer:

A is true but R is false.

Explanation— The principle of fountain experiment is to show the great solubility of the HCl gas. Hence the assertion (A) is true.

The blue litmus solution turns red due to the acidic nature of hydrogen chloride gas in the Fountain experiment. Hence reason (R) is false.

Question 7

Assertion (A): HCl gas is collected by downward delivery.

Reason (R): HCl gas is heavier than air.

Both A and R are true and R is the correct explanation of A.
Both A and R are true but R is not the correct explanation of A.
A is true but R is false.
A is false but R is true.

Exercise 8 Multiple Choice Type

Answer:

Both A and R are true and R is the correct explanation of A.

Explanation— Hydrogen chloride gas is collected by the downward delivery (upward displacement of air). Hence, the assertion (A) is true.
HCl is collected by downward delivery because it is 1.28 times heavier than air. Hence, reason (R) is true and it is the correct explanation of assertion (A).

Question 8

Assertion (A): HCl gas fumes in moist air.

Reason (R): HCl gas is highly soluble.

Both A and R are true and R is the correct explanation of A.
Both A and R are true but R is not the correct explanation of A.
A is true but R is false.
A is false but R is true.

Exercise 8 Multiple Choice Type

Answer:

Both A and R are true and R is the correct explanation of A.

Explanation— Hydrogen chloride (HCl) gas fumes in moist air because it is highly soluble in water. In the presence of moisture, HCl gas dissolves in water vapour in the air to form tiny droplets of hydrochloric acid, which appear as white fumes. So, both the assertion and the reason are true, and the reason correctly explains the assertion.

Question 9

Assertion (A): HCl gas dissolves in water as well as organic compounds like toluene.

Reason (R): HCl is a polar covalent compound.

Both A and R are true and R is the correct explanation of A.
Both A and R are true but R is not the correct explanation of A.
A is true but R is false.
A is false but R is true.

Exercise 8 Multiple Choice Type

Answer:

Both A and R are true and R is the correct explanation of A.

Explanation— Hydrogen chloride (HCl) is a polar covalent compound, which means it can dissolve in polar solvents like water due to attraction between opposite charges. Interestingly, it can also physically dissolve in some non-polar organic solvents like toluene, but without ionizing. The reason HCl can dissolve in both is due to its polar covalent nature. Hence, both the Assertion (A) and Reason (R) are true, and Reason (R) correctly explains Assertion (A).

Question 10

Assertion (A): HCl gas is used in the preparation of chlorine and chlorides.

Reason (R): Lead chloride is not produced from HCl.

Both A and R are true and R is the correct explanation of A.
Both A and R are true but R is not the correct explanation of A.
A is true but R is false.
A is false but R is true.

Exercise 8 Multiple Choice Type

Answer:

A is true but R is false.

Explanation— HCl gas dissociates into hydrogen and chlorine, when heated to 500°C and hydrogen chloride reacts with metals that come before hydrogen in the electrochemical series to form corresponding chlorides of those metals. Hence, assertion (A) is true.
When concentrated Hydrochloric acid is oxidised by strong oxidising agent like lead oxide lead chloride is formed. Hence, reason (R) is false.

Pb₃O₄ + 8HCl (conc.) ⟶ 3PbCl₂ + 4H₂O + Cl₂ ↑

Question 11

Assertion (A): HCl has sour taste.

Reason (R): HCl is highly soluble in water.

Both A and R are true and R is the correct explanation of A.
Both A and R are true but R is not the correct explanation of A.
A is true but R is false.
A is false but R is true.

Exercise 8 Multiple Choice Type

Answer:

Both A and R are true but R is not the correct explanation of A.

Explanation— Hydrogen chloride has sour (acidic) taste. Hence, the assertion (A) is true.
HCl is highly soluble in water and it can be proved by performing Fountain experiment. Hence, the reason (R) is true.

However, the high solubility of HCl in water doesn't relate to its taste, Hence, the reason (R) is not the correct explanation of assertion (A).

Exercise 8 Short Answer Type

12 questions

Question 1

A solution of hydrogen chloride in water is prepared.

The following substances are added to separate portions of the solution:

S. No.	Substances added	Gas evolved	Odour
1	Calcium carbonate
2	Magnesium ribbon
3	Manganese(IV) oxide with heating
4	Sodium sulphide

Complete the table by writing the gas evolved in case and it's odour.

Exercise 8 Short Answer Type

Answer:

S. No.	Substances added	Gas evolved	Odour
1	Calcium carbonate	*CO₂*	*odourless*
2	Magnesium ribbon	H₂	*odourless*
3	Manganese(IV) oxide with heating	*Cl₂*	*Pungent smell*
4	Sodium sulphide	*H₂S*	*Rotten egg smell*

Question 2

Complete and balance the following reactions, state whether dilute or conc. acid is used.

(a) NH₄OH + HCl ⟶

(b) NaHSO₃ + HCl ⟶

(d) Pb₃O₄ + HCl ⟶

Exercise 8 Short Answer Type

Answer:

(a) NH₄OH + HCl (dil.)⟶ NH₄Cl + H₂O

(b) NaHSO₃ + HCl (dil.) ⟶ NaCl + H₂O + SO₂

(d) Pb₃O₄ + 8HCl (conc.) ⟶ 3PbCl₂ + 4H₂O + Cl₂ ↑

Question 3

State the composition of aqua regia. State which component is the oxidizing agent in aqua regia.

Exercise 8 Short Answer Type

Answer:

Aqua regia : 1 part of conc. HNO₃ and 3 parts of conc. HCl

Nitric acid present in aqua regia oxidizes HCl to chlorine.

Question 4

How will the action of dilute hydrochloric acid enable you to distinguish between the following?

(a) Sodium carbonate and sodium sulphite

(b) Sodium thiosulphate and sodium sulphite.

Exercise 8 Short Answer Type

Answer:

(a) When Sodium carbonate is treated with dil. HCl, odourless carbon dioxide gas is produced.

Na₂CO₃ + 2HCl ⟶ 2NaCl + H₂O + CO₂ ↑

However, when sodium sulphite is treated with dil.HCl, sulphur dioxide gas with a suffocating odour (burning smell) is produced.

Na₂SO₃ + 2HCl ⟶ 2NaCl + H₂O + SO₂ ↑

(b) When sodium thiosulphate is treated with dil. HCl it produces sulphur dioxide gas and yellow sulphur precipitates.

Na₂S₂O₃ + 2HCl ⟶ 2NaCl + S + H₂O + SO₂ ↑

However, S is not produced when sodium sulphite is treated with dil.HCl.

Na₂SO₃ + 2HCl ⟶ 2NaCl + H₂O + SO₂ ↑

Question 5

MnO₂, PbO₂ and red lead react with conc. HCl acid liberates Cl₂.

What is the common property being shown by these metal oxides?

Exercise 8 Short Answer Type

Answer:

It shows that hydrochloric acid (HCl) is oxidized to chlorine (Cl₂) by strong oxidizing agents such as MnO₂, PbO₂ and red lead.

Question 6

Write an equation for the reactions of hydrochloric acid on :

(a) silver nitrate solution

(b) magnesium foil

(d) zinc carbonate

(e) manganese (IV) oxide

(f) copper oxide

Exercise 8 Short Answer Type

Answer:

(a) Silver nitrate solution
AgNO₃ + HCl ⟶ AgCl (white ppt.) + HNO₃

(b) Magnesium foil
Mg + 2HCl ⟶ MgCl₂ + H₂

(d) Zinc carbonate
ZnCO₃ + 2HCl [dil.] ⟶ ZnCl₂ + H₂O + CO₂ [g.]

(e) Manganese (IV) oxide
$\text{MnO}_2 + \underset{\text{Conc.}}{\text{4HCl}} \xrightarrow{\Delta} \text{MnCl}_2 + 2\text{H}_2\text{O} + \text{Cl}_2$ ↑

(f) Copper oxide
CuO + 2HCl ⟶ CuCl₂ + H₂O.

Question 7

Write the balanced equations for the reaction of dilute hydrochloric acid with each of the following:

(a) Iron

(b) Sodium hydrogen carbonate

(d) magnesium sulphite

Exercise 8 Short Answer Type

Answer:

The balanced equation are :

(a) Iron
Fe + 2HCl (dil.) ⟶ FeCl₂ + H₂ ↑

(b) Sodium hydrogen carbonate
NaHCO₃ + HCl ⟶ NaCl + H₂O + CO₂ ↑

(d) Magnesium sulphite
MgSO₃ + 2HCl ⟶ MgCl₂ + H₂O + SO₂ ↑

Question 8

How would you distinguish between dilute HCl and dilute HNO₃, by addition of only one solution.

Exercise 8 Short Answer Type

Answer:

When silver nitrate soln. is added to dil. HCl, curdy white ppt. of silver chloride is formed whereas, there is no reaction when silver nitrate soln. is added to dil. HNO₃.

AgNO₃ + HCl ⟶ AgCl (white ppt.) + HNO₃

AgNO₃ + HNO₃ ⟶ no reaction

Question 9

State one appropriate observation when :

(a) Copper sulphide is treated with dilute hydrochloric acid.

(b) A few drops of dil. HCl are added to AgNO₃ solution. followed by addition of NH₄OH solution.

(d) A small piece of zinc is added to dilute hydrochloric acid.

(e) Dilute HCl is added to sodium carbonate crystals.

(f) Concentrated HCl is added to manganese dioxide.

Exercise 8 Short Answer Type

Answer:

(a) A colourless gas having smell of rotten eggs is given off. The gas evolved is H₂S
CuS + 2HCl ⟶ CuCl₂ + H₂S ↑

(b) Curdy white precipitate of silver chloride [AgCl] is obtained, which is soluble in excess of NH₄OH.
AgNO₃ + HCl ⟶ AgCl ↓ + HNO₃
AgCl + 2NH₄OH ⟶ [Ag(NH₃)₂Cl)] + 2H₂O

(d) Hydrogen gas is evolved with bubbles and it burns with a pop sound
Zn + 2HCl ⟶ ZnCl₂ + H₂ ↑

(e) Effervescence of CO₂ seen which turns lime water milky.
Na₂CO₃ + 2HCl ⟶ 2NaCl + H₂O + CO₂ ↑

(f) When concentrated hydrochloric acid is added to manganese dioxide (MnO₂), a greenish-yellow gas (chlorine gas) is evolved with effervescence.
MnO₂ + 4HCl (conc.) $\xrightarrow{\Delta}$ MnCl₂ + 2H₂O + Cl₂↑

Question 10

Write balanced chemical equations for the following :

(a) Sodium thiosulphate is reacted with dilute hydrochloric acid.

(b) Calcium bicarbonate reacts with dilute hydrochloric acid.

(d) Action of dilute hydrochloric acid on sodium sulphide.

(e) Action of hydrochloric acid on sodium bicarbonate.

Exercise 8 Short Answer Type

Answer:

(a) Na₂S₂O₃ + 2HCl ⟶ 2NaCl + S + H₂O + SO₂ ↑

(b) Ca(HCO₃)₂ + 2HCl ⟶ CaCl₂ + 2H₂O + 2CO₂ ↑

(d) Na₂S + 2HCl ⟶ 2NaCl + H₂S [g.] ↑

(e) NaHCO₃ + HCl ⟶ NaCl + H₂O + CO₂ ↑

Question 11

Give balanced equations with conditions, if any, for the following conversions

(a) Sodium Chloride ⟶ Hydrogen Chloride

(b) Hydrogen Chloride ⟶ Iron (II) chloride

(d) Hydrogen Chloride ⟶ Lead chloride.

Exercise 8 Short Answer Type

Answer:

(a) $\text{NaCl} + \text{H}_2\text{SO}_4 \xrightarrow{\lt 200 \degree\text{C}} \text{NaHSO}_4 + \text{HCl [g]}$ ↑

(b) Fe + 2HCl (dil.) ⟶ FeCl₂ + H₂ [g]

(d) $\text{PbO}_2 + 4\text{HCl} \xrightarrow{\Delta} \text{PbCl}_2 + 2\text{H}_2\text{O} + \text{Cl}_2$ ↑

Question 12

Explain why

(a) anhydrous HCl is a poor conductor while aqueous HCl is an excellent conductor.

(b) when the stopper of a bottle full of hydrogen chloride gas is opened there are fumes in the air.

(c) a solution of hydrogen chloride in water turns blue litmus red and conducts electricity, while a solution of the same gas in toluene

(i) has no effect on litmus, and

(ii) does not conduct electricity.

(d) thick white fumes are formed when a glass rod dipped in NH₄OH is brought near the mouth of a bottle full of HCl gas.

(e) dry hydrogen chloride gas does not affect a dry strip of blue litmus paper, but it turns red in the presence of a drop of water.

(f) hydrogen chloride gas is not collected over water.

(g) dilute hydrochloric acid cannot be concentrated by boiling beyond 22.2%.

(h) Hydrogen chloride gas cannot be dried over quick lime.

Exercise 8 Short Answer Type

Answer:

(a) Anhydrous HCl is a gas and does not contain any ions, hence it is a poor conductor of electricity. On the other hand, aqueous HCl (HCl dissolved in water) forms ions in solution, and thus becomes an excellent conductor of electricity.

HCl + H₂O ⟶ H₃O⁺ + Cl^-

(b) When hydrogen chloride gas is exposed to air, it gives white fumes, due to the formation of hydrochloric acid on dissolving in atmospheric water vapour.

HCl + H₂O ⟶ H₃O⁺ + Cl^-

These ions are responsible for conducting electricity and turning blue litmus red, due to the presence of hydronium [H₃O⁺] ions which make aqueous solution of HCl acidic in nature.

Toluene is an organic solvent and HCl is a covalent compound. A solution of HCl in toluene contains only molecules and not ions due to which it does not conduct electricity. The absence of hydronium [H₃O⁺] ions make the solution neutral and it does not effect litmus paper.

(d) When a glass rod dipped in ammonium hydroxide (NH₄OH) is brought near the mouth of a bottle full of HCl gas, then it leads to the formation of dense white fumes due to the production of ammonium chloride.

NH₄OH + HCl ⟶ NH₄Cl + H₂O

(e) Dry hydrogen chloride gas does not contain any ions. Due to the absence of hydronium [H₃O⁺] ions, it is neutral and does not affect a dry strip of blue litmus paper. On the other hand, in the presence of a drop of water, HCl dissolves in it and dissociates into hydronium [H₃O⁺] ions and chloride ions [Cl^-]

HCl + H₂O ⟶ H₃O⁺ + Cl^-

The presence of hydronium [H₃O⁺] ions makes the aqueous solution acidic and blue litmus turns red.

(f) Hydrogen chloride gas is not collected over water since it is highly soluble in water.

(g) Hydrochloric acid forms a constant boiling mixture at 110°C, 22.2% by weight. On boiling further, the mixture evolves out the vapours of both acid and water in the same proportion as in the liquid.

Hence, dilute HCl cannot be concentrated beyond 22.2% by boiling.

(h) Quicklime [CaO] is alkaline in nature and it reacts with HCl forming the respective chloride. Hence, it can't be used as a drying agent.

Exercise 8 Very Short Answer Type

4 questions

Question 1

Fill in the blank from the choices in the bracket :

(a) Quicklime is not used to dry HCl gas because CaO is ............... [alkaline/acidic/neutral]

(b) When sodium chloride is heated with concentrated sulphuric acid below 200°C, one of the product formed is ............... (sodium hydrogen sulphate / sodium sulphate / chlorine).

Exercise 8 Very Short Answer Type

Answer:

(a) Quicklime is not used to dry HCl gas because CaO is alkaline.

(b) When sodium chloride is heated with concentrated sulphuric acid below 200°C, one of the product formed is sodium hydrogen sulphate.

Question 2

Name :

(a) a black metallic oxide which reacts with hydrochloric acid to give a coloured solution.

(b) two colourless gases, which when mixed produce a white solid

(d) a chloride which is soluble in excess of ammonium hydroxide.

(e) the chemical in which gold can be dissolved.

(f) the experiment which demonstrates that hydrogen chloride is soluble in water.

(g) the gas produced when chlorine water is exposed to sunlight.

(h) the acid which on mixing with silver nitrate solution produces a white precipitate which is soluble in excess of ammonium hydroxide.

(i) the gas which produces dense white fumes with ammonia gas.

(j) an element which reacts with hydrogen to form compound which is strongly acidic in water.

Exercise 8 Very Short Answer Type

Answer:

(a) Copper oxide (CuO)

(b) Hydrogen chloride and Ammonia

(d) Silver chloride

(e) Aqua Regia

(f) Fountain experiment

(g) Oxygen gas

(h) Dilute hydrochloric acid

(i) Hydrogen chloride

(j) Chlorine

Explanation

(a) Copper oxide (CuO) is black, reacts with HCl to form blue-coloured copper(II) chloride solution.
CuO + 2HCl ⟶ CuCl₂ + H₂O

(b) NH₃ (g) + HCl (g) ⟶ NH₄Cl (white solid)

(d) AgCl dissolves in excess NH₄OH due to formation of [Ag(NH₃)₂]⁺ complex.
AgCl + 2NH₄OH ⟶ [Ag(NH₃)₂]⁺Cl^- + 2H₂O

(e) Aqua regia (1 part of conc. HNO₃ and 3 parts of conc. HCl) dissolves gold.

(f) Fountain experiment vividly shows HCl gas dissolving in water, creating a fountain effect due to pressure drop.

(g) When chlorine water is exposed to sunlight, chlorine reacts with water to form hypochlorous acid. This acid then breaks apart to give nascent oxygen (O) and hydrochloric acid (HCl). The nascent oxygen combines to form Oxygen gas:
Cl₂ + H₂ $\xrightarrow{\text{sunlight}}$ HClO + HCl
HClO $\xrightarrow{\text{sunlight}}$ HCl + [O] (nascent oxygen)
[O] + [O] ⟶ O₂

(h) AgNO₃ + HCl ⟶ AgCl (white ppt.) + HNO₃ which dissolves in excess NH₄OH.

(i) NH₃ [g] + HCl [g] ⟶ NH₄Cl [s]

(j) H₂ + Cl₂ ⟶ 2HCl; HCl is strongly acidic in water.

Question 3

Identify the gas evolved when :

(i) Potassium sulphite is treated with dilute hydrochloric acid.

(ii) Concentrated hydrochloric acid is made to react with manganese dioxide.

Exercise 8 Very Short Answer Type

Answer:

(i) Sulphur dioxide gas

(ii) Chlorine gas
$\text{MnO}_2 + 4\text{HCl} \xrightarrow{\Delta} \text{MnCl}_2 + 2\text{H}_2\text{O} + \text{Cl}_2$ ↑

Question 4

Solution A reacts with an acid B (which gives greenish yellow gas on reacting with oxidising agents like Pb₃O₄) to give white precipitate C insoluble in nitric acid but soluble in ammonium hydroxide. Name A, B and C.

Exercise 8 Very Short Answer Type

Answer:

A → Silver nitrate
B → Hydrochloric acid
C → Silver chloride

Explanation — Solution A is silver nitrate which reacts with acid B i.e., Hydrochloric acid to give a white precipitate C of AgCl which is insoluble in nitric acid but soluble in ammonium hydroxide.

AgNO₃ + HCl ⟶ AgCl ↓ + HNO₃

AgNO₃ + HNO₃ ⟶ no reaction

AgCl + 2NH₄OH ⟶ [Ag(NH₃)₂Cl)] + 2H₂O