Study of Compounds — Hydrogen Chloride

Equations Worksheet

Question 1

Answer

Question 2

Answer

Question 3

Answer

Questions

Question 1(2007)

Write a balanced equation for Sodium chloride from sodium carbonate soln. and dilute hydrochloric acid.

Answer

Na₂CO₃ + 2HCl [dil.] ⟶ 2NaCl + H₂O + CO₂ [g.]

Question 2(2007)

Of the two gases, NH₃ and HCl, which is more dense. Name the method of collection of this gas.

Answer

Hydrogen chloride gas is denser than NH₃.
Reason — V.D. of NH₃ = 8.5 and that of HCl = 18.25

HCl gas is collected by upward displacement of air.

Question 3(2007)

Give one example of a reaction between the above two gases which produces a solid.

Answer

NH₃ [g] + HCl [g] ⟶ NH₄Cl (s-solid)

When a gas jar containing HCl gas in inverted over a jar full of ammonia gas, dense white fumes are formed. These fumes consist of particles of solid ammonium chloride suspended in air.

Question 4(2007)

Write equations for the reaction of dil. HCl with each of the following :

(i) iron

(ii) sodium hydrogen carbonate

(iii) iron [II] sulphide

(iv) sodium sulphite

Answer

(i) Fe + 2HCl ⟶ FeCl₂ + H₂

(ii) NaHCO₃ + HCl ⟶ NaCl + H₂O + CO₂

(iii) FeS + 2HCl ⟶ FeCl₂ + H₂S

(iv) Na₂SO₃ + 2HCl ⟶ 2NaCl + H₂O + SO₂ [g]

Question 1(2008)

What property of hydrogen chloride is demonstrated when it is collected by downward delivery [upward displacement]. Why is hydrogen chloride not collected over water.

Answer

Hydrogen chloride is 1.28 times heavier than air, hence it is collected by downward delivery [upward displacement]. Hydrogen chloride is not collected over water since it is highly soluble in water.

Question 2(2008)

Write equations for the reactions :

(i) dil. HCl and sodium thiosulphate.

(ii) dil. HCl and lead nitrate soln.

Answer

(i) Na₂S₂O₃ + 2HCl ⟶ 2NaCl + SO₂ + S + H₂O

(ii) Pb(NO₃)₂ + 2HCl ⟶ PbCl₂ ↓ + 2HNO₃

Question 1(2009)

Name the gas evolved - The gas produced by the action of concentrated sulphuric acid on sodium chloride.

Answer

Hydrogen chloride (HCl)

$\text{NaCl} + \text{H}_2\text{SO}_4 \xrightarrow{\lt 200 \degree\text{C}} \text{NaHSO}_\text{4} + \text{HCl [g]}$

Question 2(2009)

Match each substance A to E listed below with the appropriate description given below :

[A] Sulphur
[B] Silver chloride
[C] Hydrogen chloride
[D] Copper [II] Sulphate
[E] Graphite.

(i) A covalent compound which behaves like an ionic compound in aqueous solution.
(ii) A compound which is insoluble in cold water but soluble in excess of ammonia solution.

Answer

(i) [C] Hydrogen chloride
(ii) [B] Silver chloride

Question 3(2009)

Write a balanced equation for each of the following :

(i) Red lead is warmed with concentrated hydrochloric acid.

(ii) Magnesium metal is treated with dilute hydrochloric acid.

Answer

(i) $\text{Pb}_3\text{O}_4 + 8\text{HCl} \xrightarrow{\Delta} 3\text{PbCl}_2 + 4\text{H}_2\text{O} + \text{Cl}_2$

(ii) Mg + 2HCl ⟶ MgCl₂ + H₂

Question 4(2009)

Correct the statement:

HCl acid is prepared in the lab. by passing hydrogen chloride directly through water.

Answer

HCl acid is prepared in the lab. by passing hydrogen chloride gas in water using a special funnel arrangement.

Question 1(2010)

Select the correct answer from A, B, C and D.

(i) Aqua regia is a mixture of :

A : Dilute hydrochloric and conc. nitric acid
B : Conc. hydrochloric and dilute nitric acid
C : One part of conc. hydrochloric acid and 3 parts of conc. nitric acid.
D : 3 parts of conc. hydrochloric acid and 1 part of conc. nitric acid

Answer

D : 3 parts of conc. hydrochloric acid and 1 part of conc. nitric acid

Question 2(2010)

State your observation when :
A glass rod dipped in NH₄OH soln. is brought near an open bottle containing conc. HCl

Answer

Dense white fumes of ammonium chloride are formed when a glass rod dipped in NH₄OH soln. is brought near an open bottle containing conc. HCl

$\underset{\text{[aq.]}}{\text{NH}_3} + \underset{\text{[vapour]}}{\text{HCl}} \longrightarrow \underset{\text{[dense white fumes]}}{\text{NH}_4\text{Cl}}$

Question 3(2010)

(i) State the salt and the acid, used in the laboratory preparation of hydrogen chloride.

(ii) Give the equation for the preparation.

(iii) State a method to prove that the gas jar used for collection of HCl gas is filled with hydrogen chloride.

(iv) Observing the method of collection of the gas, state what you can tell about the density of hydrogen chloride.

Answer

(i) Salt — Sodium Chloride [NaCl], Acid — Sulphuric acid [H₂SO₄]

(ii) $\text{NaCl} + \text{H}_2\text{SO}_4 \xrightarrow{\lt 200 \degree\text{C}} \text{NaHSO}_\text{4} + \text{HCl}$

(iii) A glass rod dipped in NH₄OH soln. is brought near the mouth of the gas jar 'Y'. If the gas jar is full with HCl gas then dense white fumes of ammonium chloride are formed.

$\underset{\text{[aq.]}}{\text{NH}_3} + \underset{\text{[vapour]}}{\text{HCl}} \longrightarrow \underset{\text{[dense white fumes]}}{\text{NH}_4\text{Cl}}$

(iv) This method indicates that HCl gas is heavier than air.

Question 4(2010)

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

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 5(2010)

Name two gases which can be used in the study of the fountain experiment. State the common property demonstrated by the fountain experiment ?

Answer

Dry hydrogen chloride gas (HCl) and Ammonia (NH₃) gas can be used in the study of the fountain experiment.

High solubility of HCl gas in water is the common property demonstrated by the fountain experiment.

Question 1(2011)

Choose the correct answer:

Hydrogen chloride gas being highly soluble in water is dried by :

1. Anhydrous calcium chloride
2. Phosphorous pentaoxide
3. Quick lime
4. Conc. sulphuric acid.

Answer

Concentrated 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 2(2011)

Write balanced equation of dil. HCl with Calcium bicarbonate.

Answer

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

Question 3(2011)

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

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

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

(iii) Write balanced chemical equations for the laboratory preparation of HCl gas when the reactants are :

    (A) below 200°C

    (B) above 200°C

Answer

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

(ii) The reasons are :

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

(iii) The equations are:

(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 1(2012)

Rewrite the correct statement with the missing word/s : Aqua regia contains one part by volume of nitric acid and three parts by volume of hydrochloric acid.

Answer

Aqua regia contains one part by volume of conc. nitric acid and three parts by volume of conc. hydrochloric acid.

Question 2(2012)

Give reason for the following : Hydrogen chloride gas cannot be dried over quick lime.

Answer

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.

Question 3(2012)

Give a balanced equation for the reaction : Conc. hydrochloric acid and potassium permanganate solution.

Answer

$2\text{KMnO}_4 + 16\text{HCl} \xrightarrow{\Delta} 2\text{KCl} + 2\text{MnCl}_2 + 8\text{H}_2\text{O}+ 5\text{Cl}_2$

Question 4(2012)

Give balanced equations with conditions, if any, for the following conversions A to D.

A : Sodium Chloride ⟶ Hydrogen Chloride

B : Hydrogen Chloride ⟶ Iron (II) chloride

C : Hydrogen Chloride ⟶ Ammonium chloride

D : Hydrogen Chloride ⟶ Lead chloride.

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]

C: NH₄OH + HCl (dil.)⟶ NH₄Cl + H₂O

D: $\text{PbO}_2 + 4\text{HCl} \xrightarrow{\Delta} \text{PbCl}_2 + 2\text{H}_2\text{O} + \text{Cl}_2$

Question 1(2013)

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.

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 2(2013)

State one appropriate observation for :

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

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

Answer

(i) A colourless gas having smell of rotten eggs is given off. The gas evolved is H₂S

CuS + 2HCl ⟶ CuCl₂ + H₂S

(ii) 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

Question 1(2014)

Fill in the blank from the choices in the bracket :

Quicklime is not used to dry HCl gas because ............... [CaO is alkaline, CaO is acidic, CaO is neutral]

Answer

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

Question 2(2014)

Write the balanced equation for:
Action of dilute hydrochloric acid on sodium sulphide.

Answer

Action of dilute hydrochloric acid on sodium sulphide.

Na₂S + 2HCl ⟶ 2NaCl + H₂S [g.]

Question 3(2014)

State your observation:
Dilute HCl is added to sodium carbonate crystals.

Answer

Na₂CO₃ + 2HCl ⟶ 2NaCl + H₂O + CO₂ ↑

Effervescence of CO₂ seen which turns lime water milky

Question 4(2014)

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

(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.

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 1(2015)

Select from the gases — ammonia, ethane, hydrogen chloride, hydrogen sulphide, ethyne — The gas which produces dense white fumes with ammonia gas.

Answer

Hydrogen chloride

NH₃ [g] + HCl [g] ⟶ NH₄Cl (s-solid)

When a gas jar containing HCl gas in inverted over a jar full of ammonia gas, dense white fumes are formed. These fumes consists of particles of solid ammonium chloride suspended in air.

Question 2(2015)

Identify the acid which on mixing with AgNO₃ soln. gives a white precipitate, soluble in excess ammonium hydroxide.

Answer

Dilute hydrochloric acid

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

Question 3(2015)

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

(i) Write the equation for it's preparation mentioning the condition required.

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

(iii) State a safety precaution taken during the preparation of hydrochloric acid.

Answer

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

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

(ii) 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.

(iii) The precautions taken are:

1. The reaction mixture is initially heated very slowly to control the evolution of HCl gas.
2. The lower end of the thistle funnel should dip below the acid in the flask otherwise the HCl gas obtained will escape out from the thistle funnel.

Question 1(2016)

Select the correct answer from A, B, C and D : The aim of the Fountain experiment is to prove that :

(A) HCl turns blue litmus red

(B) HCl is denser than air

(C) HCl is highly soluble in water

(D) HCl fumes in moist air.

Answer

(C) HCl is highly soluble in water

Question 2(2016)

Fill in the blank : ...............[AgCl / PbCl₂], a white precipitate is soluble in excess NH₄OH.

Answer

AgCl, a white precipitate is soluble in excess NH₄OH.

Question 3(2016)

Write balanced chemical equation for : Action of hydrochloric acid on sodium bicarbonate.

Answer

NaHCO₃ + HCl ⟶ NaCl + H₂O + CO₂ ↑

Question 4(2016)

State your observations when dilute hydrochloric acid is added to :

(i) Lead nitrate soln. and the mixture is heated.

(ii) Copper carbonate.

(iii) Sodium thiosulphate.

Answer

(i) White precipitate of PbCl₂ is formed which is soluble in hot water.

Pb(NO₃)₂ + 2HCl ⟶ PbCl₂ ↓ + 2HNO₃

(ii) Effervescence of CO₂ seen which turns lime water milky

CuCO₃ + 2HCl ⟶ CuCl₂ + H₂O + CO₂

(iii) Yellow particles of S precipitate.

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

Question 5(2016)

Identify the gas evolved and give the chemical test when dilute hydrochloric acid reacts with :

(i) Sodium sulphite.

(ii) Iron [II] sulphide.

Answer

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

Na₂SO₃ + 2HCl ⟶ 2NaCl + H₂O + SO₂ [g]

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

FeS + 2HCl ⟶ FeCl₂ + H₂S

Question 1(2017)

Fill in the blanks –

Potassium sulphite on reacting with hydrochloric acid, releases ............... gas. [Cl₂, SO₂, H₂S]

Answer

Potassium sulphite on reacting with hydrochloric acid, releases SO₂ gas.

Question 2(2017)

Identify the substance underlined – A solid formed by the reaction of two gases, one of which is acidic and the other basic in nature.

Answer

Ammonium chloride.

NH₃ [g] + HCl [g] ⟶ NH₄Cl (s-solid)

Question 3(2017)

State one relevant observation – Action of dilute hydrochloric acid on iron [II] sulphide.

Answer

H₂S gas is evolved. It has a foul smell like rotten eggs.

FeS + 2HCl [g] ⟶ FeCl₂ + H₂S

Question 4(2017)

Certain blanks spaces are left in the following table as A & B. Identify each of them.

Answer

A : The products are sodium hydrogen sulphate (NaHSO₄) and HCl gas.

B : HCl gas is collected by the upward displacement of air method.

Question 1(2018)

Write a balanced chemical equation for - Action of dilute hydrochloric acid on magnesium sulphite.

Answer

MgSO₃ + 2HCl ⟶ MgCl₂ + H₂O + SO₂ [g]

Question 2(2018)

State one relevant observation - Lead nitrate solution is mixed with dilute hydrochloric acid and heated.

Answer

White precipitate of PbCl₂ is formed which is soluble in hot water.

Pb(NO₃)₂ + 2HCl ⟶ PbCl₂ + 2HNO₃

Question 3(2018)

Name the gas that is produced during - Action of dilute hydrochloric acid on sodium sulphide.

Answer

H₂S gas is evolved.

Na₂S + 2HCl ⟶ 2NaCl + H₂S [g.]

Question 4(2018)

Fill in the blank with the correct choice given in the bracket - Dry hydrogen chloride gas can be collected by ............... displacement of air. [downward/upward]

Answer

Dry hydrogen chloride gas can be collected by upward displacement of air.

Question 5(2018)

Name the acid used for the preparation of - hydrogen chloride gas in the laboratory. State why this particular acid is preferred to other acids.

Answer

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

Question 6(2018)

Write a balanced chemical equation for - The laboratory preparation of hydrogen chloride gas.

Answer

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

Question 7(2018)

For the preparation of hydrochloric acid in the laboratory —

(i) State why direct absorption of hydrogen chloride gas in water is not feasible.

(ii) State what arrangement is used to dissolve hydrogen chloride gas in water.

Answer

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

1. Hydrogen chloride gas is extremely soluble in water.
2. 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.
3. 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.

(ii) Special funnel arrangement is used for avoiding back suction. It (a) Prevents or minimizes back-suction of water (b) Provides a large surface area for absorption of HCl gas.

1. The rim of the funnel is placed so that it just touches the trough containing water. If back-suction occurs, the water rises up the funnel and the level outside the funnel falls, creating an air gap between the rim of the funnel and the surface of water.
2. The pressure outside and inside equalize and the water which had risen in the funnel falls down again. This process continues till the water in the trough is saturated with hydrogen chloride gas resulting in the formation of hydrochloric acid.
3. Hence, hydrochloric acid is not prepared in the laboratory by passing hydrogen chloride gas directly through water, but prepared using a special funnel arrangement.

Question 1(2019)

Choose the correct answer from the options A, B, C and D given :

The drying agent used to dry HCl gas is :

A : Conc. H₂SO₄
B : ZnO
C : Al₂O₃
D : CaO

Answer

Conc. H₂SO₄

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 2(2019)

Fill in the blanks with the choices given in the bracket:

When sodium chloride is heated with concentrated sulphuric acid below 200°C, one of the products formed is ............... [sodium hydrogen sulphate / sodium sulphate / chlorine]

Answer

When sodium chloride is heated with concentrated sulphuric acid below 200°C, one of the products formed is sodium hydrogen sulphate

Question 3(2019)

State one observation for the following:

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

Answer

Effervescence of H₂ gas can be seen.

Zn + 2HCl ⟶ ZnCl₂ + H₂

Question 1(2020)

State one relevant reason for:
Hydrogen chloride gas fumes in moist air.

Answer

Due to its high solubility, HCl gas fumes in moist air and forms a mist of droplets of HCl acid.

Question 2(2020)

Complete the following by selecting the correct option from the choices given.

(i) The indicator which does not change colour on passage of HCl gas is .............. [methyl orange, moist blue litmus, phenolphthalein].

(ii) The acid which cannot act as an oxidizing agent is ............... [conc. H₂SO₄, conc. HNO₃, conc. HCl]

Answer

(i) The indicator which does not change colour on passage of HCl gas is phenolphthalein.

(ii) The acid which cannot act as an oxidizing agent is conc. HCl

Question 3(2020)

Hydrogen chloride gas is prepared in the laboratory using conc. H₂SO₄ and NaCl. 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 conc. nitric acid.

(iii) How is the gas collected.

(iv) Name the drying agent not used for drying the gas.

Answer

(i) Balanced chemical equation for the reaction are :

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

(ii) 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.
Conc. nitric acid cannot be used in place of conc. H₂SO₄ since it is volatile and may volatize out along with the hydrogen chloride.

(iii) The gas is collected by upward displacement of air method.

(iv) Quicklime (CaO) and phosphorous pentoxide [P₂O₅] are not used as drying agent, since they react with HCl forming their respective chlorides.

Complete the Statements

Question 1

Complete the statements given below pertaining to hydrogen chloride gas or hydrochloric acid:

1. Hydrogen chloride gas is not dried using ............... [conc.H₂SO₄, CaO].
2. Hydrogen chloride gas on heating above 500°C gives hydrogen and chlorine. The reaction is an example of ............... [thermal decomposition, thermal dissociation].
3. Iron reacts with hydrogen chloride gas forming ............. [iron (II) chloride, iron (III) chloride] and hydrogen. The reaction is an example of ............... [double decomposition, synthesis, simple displacement].
4. Hydrogen chloride and water are examples of ............... [polar covalent compounds, non-polar covalent compounds] and a solution of hydrogen chloride in water ............... [contains, does not contain] free ions.
5. Addition of ............... [sodium nitrate, zinc nitrate, silver nitrate] to hydrochloric acid, gives an insoluble precipitate of the respective chloride. This precipitate is ............... [soluble, insoluble] in ammonium hydroxide and ............... [soluble, insoluble] in dilute nitric acid.
6. Addition of ............... [iron (III) sulphide, iron (II) sulphide, iron pyrites] to dilute hydrochloric acid results in liberation of hydrogen sulphide gas.
7. Aqua regia is a mixture of ............... [one, two, three] part/s of concentrated nitric acid and ............... [one, two, three] part/s of concentrated hydrochloric acid by .............. [weight, volume]. In aqua regia, nitric acid ............... [oxidises, reduces] hydrochloric acid to chlorine.
8. Hydrochloric acid can be converted into chlorine by heating with ............... [calcium oxide, lead (II) oxide, lead (IV) oxide] which acts as a/an ............... [oxidising, reducing] agent.

Answer

1. Hydrogen chloride gas is not dried using CaO.
2. Hydrogen chloride gas on heating above 500°C gives hydrogen and chlorine.The reaction is an example of thermal dissociation.
3. Iron reacts with hydrogen chloride gas forming iron (II) chloride and hydrogen. The reaction is an example of simple displacement.
4. Hydrogen chloride and water are examples of polar covalent compounds and a solution of hydrogen chloride in water contains free ions.
5. Addition of silver nitrate to hydrochloric acid, gives an insoluble precipitate of the respective chloride. This precipitate is soluble in ammonium hydroxide and insoluble in dilute nitric acid.
6. Addition of iron (II) sulphide to dilute hydrochloric acid results in liberation of hydrogen sulphide gas.
7. Aqua regia is a mixture of one part/s of concentrated nitric acid and three part/s of concentrated hydrochloric acid by volume. In aqua regia, nitric acid oxidises hydrochloric acid to chlorine.
8. Hydrochloric acid can be converted into chlorine by heating with lead (IV) oxide which acts as an oxidising agent.

Additional Questions

Question 1

Give a reason why:

(a) gastric juices of mammals are acidic

(b) HCl is considered a polar covalent compound.

Answer

(a) HCl is present in gastric juices of mammals, hence the gastric juices of mammals are acidic. It helps in digestion.

(b) Due to difference in electronegativities of H and Cl the bond in HCl is polar covalent.

Question 2

Give the equation for preparation of HCl gas by synthesis. State two conditions involved in the synthesis.

Answer

Moist hydrogen gas combines with chlorine in the presence of diffused sunlight.

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

1. The reaction is explosive in direct sunlight and negligible in the dark. Moisture acts as a catalyst in the above synthesis reaction.
2. Burning jet of hydrogen also burns in chlorine forming hydrogen chloride.

Question 3

Give a balanced equation for preparation of HCl gas in the laboratory from sodium chloride.

Answer

Below is the balanced equation for preparation of HCl gas in the laboratory from sodium chloride:

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

Question 4

In the laboratory preparation of HCl from sodium chloride, state why the following are preferred –

(i) Conc. H₂SO₄ as a reactant

(ii) Temp. below 200°C

(iii) Conc. H₂SO₄ as a drying agent.

Answer

(i) 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

(ii) The fuel is not wasted, the glass apparatus does not crack and sodium sulphate does not form hard crust, which in turn may stick to the glass and will be difficult to remove. Therefore, temperature below 200°C is used.

(iii) 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 5

State with reasons the method of collection of HCl gas in the laboratory.

Answer

Dry HCl gas is collected by the upward displacement of air because it is 1.28 times heavier than air. It is highly soluble in water, hence not collected over water.

Question 6

Compare the density of HCl gas with air and state the solubility of HCl gas in water.

Answer

V.D of HCl = 18.25 and air = 14.4. HCl gas is highly soluble in water.

Question 7

State why HCl gas forms a mist of droplets of HCl acid in moist air.

Answer

Due to high solubility, HCl gas fumes in moist air and forms a mist of droplets of HCl acid.

Question 8

State what the fountain experiment demonstrates with reference to HCl gas.

Answer

The high solubility of HCl gas in water is demonstrated by the Fountain experiment.

Question 9

State the colour change in three different indicators in presence of HCl gas.

Answer

Action on indicators:

Question 10

Give a balanced equation for thermal dissociation of

(i) a gas

(ii) a solid [both containing the chloride ion].

Answer

(i) $2\text{HCl} \xrightleftharpoons{\gt 500 \degree\text{C}} \text{H}_\text{2} + \text{Cl}_\text{2}$

(ii) $\text{NH}_4\text{Cl} \xrightarrow{\Delta} \text{NH}_3 + \text{HCl}$

Question 11

Give the equation and state the observation seen when HCl gas reacts with ammonia.

Answer

NH₃ [g] + HCl [g] ⟶ NH₄Cl (s-solid)

When a gas jar containing HCl gas in inverted over a jar full of ammonia gas dense white fumes are formed. These fumes consists of particles of solid ammonium chloride suspended in air.

Question 12

Convert iron to iron (II) chloride using HCl gas.

Answer

Fe + 2HCl ⟶ FeCl₂ + H₂

Question 13

Explain the arrangement (i) not used (ii) used – for converting HCl gas into HCl acid.

Answer

Hydrochloric acid is prepared by dissolving hydrogen chloride gas in water using a special funnel arrangement.

(i) Direct absorption of HCl gas in water using a delivery tube causes back suction. Hence, it is not used for preparing HCl acid from HCl gas.

1. Hydrogen chloride gas is extremely soluble in water.
2. 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.
3. 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.

(ii) Special funnel arrangement is used for converting HCl gas into HCl acid as it avoids back suction. It:
    (a) Prevents or minimizes back-suction of water.
    (b) Provides a large surface area for absorption of HCl gas.

1. The rim of the funnel is placed so that it just touches the trough containing water. If back-suction occurs, the water rises up the funnel and the level outside the funnel falls, creating an air gap between the rim of the funnel and the surface of water.
2. The pressure outside and inside equalize and the water which had risen in the funnel falls down again. This process continues till the water in the trough is saturated with hydrogen chloride gas resulting in the formation of hydrochloric acid.
3. Hence, hydrochloric acid is not prepared in the laboratory - by passing hydrogen chloride gas directly through water, but prepared using a special funnel arrangement.

Question 14

Explain the term 'constant boiling mixture'.

Answer

A solution which boils without any change in it's composition is known as the constant boiling mixture. A solution of HCl in water forms a constant boiling mixture at 110° C.

Question 15

State why dilute HCl cannot be concentrated beyond a certain concentration by boiling.

Answer

On boiling, 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 a certain concentration by boiling.

Question 16

Name the ions obtained when HCl dissociates in aqueous solution.

Answer

The ions obtained are hydronium ions (H₃O⁺) and chloride ions (Cl^-)

HCl + H₂O ⟶ H₃O⁺ + Cl^-

Question 17

Name the ion responsible for acidic nature of HCl acid.

Answer

The presence of hydrogen ions [H⁺] in HCl imparts acidic properties to an aqueous solution of hydrochloric acid.

Question 18

State which of two — a solution of HCl in water or in toluene is an electrolyte, giving reasons.

Answer

Water being a polar solvent, ionizes the polar covalent HCl molecule into free ions. Hence, the solution of HCl in water exhibits acidic properties and is an electrolyte whereas toluene not being a polar solvent does not dissociate HCl molecule into free ions. Hence, the solution of HCl in toluene does not exhibit acidic properties and is a non electrolyte.

Question 19

Give four different word equations relating to acidic properties of an aq. soln. of HCl gas.

Answer

1. Magnesium + Hydrochloric acid ⟶ Magnesium chloride + Hydrogen
2. Copper oxide + Hydrochloric acid ⟶ Copper chloride + Water
3. Sodium carbonate + Hydrochloric acid ⟶ Sodium chloride + Water + Carbon dioxide gas
4. Magnesium sulphite + Hydrochloric acid ⟶ Magnesium chloride + Water + sulphur dioxide gas

Question 20

Give balanced equations to obtain

(i) H₂

(ii) CO₂

(iii) SO₂

(iv) H₂S

from dil. HCl.

Answer

(i) Mg + 2HCl ⟶ MgCl₂ + H₂

(ii) NaHCO₃ + HCl ⟶ NaCl + H₂O + CO₂ [g]

(iii) Na₂SO₃ + 2HCl ⟶ 2NaCl + H₂O + SO₂ [g]

(iv) FeS + 2HCl ⟶ FeCl₂ + H₂S

Question 21

Convert two soluble metallic nitrates to insoluble metallic chlorides using dil. HCl.

Answer

(i) AgNO₃ + HCl ⟶ AgCl ↓ + HNO₃

(ii) Pb(NO₃)₂ + 2HCl ⟶ PbCl₂ ↓ + 2HNO₃

Question 22

State how you would prove that HCl contains :

(i) hydrogen – using an active metal below magnesium

(ii) chlorine – using an oxidising agent not containing lead.

Answer

(i) Fe + 2HCl ⟶ FeCl₂ + H₂

(ii) MnO₂ + 4HCl ⟶ MnCl₂ + 2H₂O + Cl₂

Question 23

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

Answer

Aqua regia is a mixture of 1 part of conc. HNO₃ and 3 parts of conc. HCl [by vol.]

Nitric acid is the oxidizing agent in aqua regia.

Question 24

Convert hydrochloric acid to nascent chlorine.

Answer

HNO₃ + 3HCl ⟶ 2H₂O + NOCl + 2[Cl] [nascent chlorine]

Question 25

State why aqua regia dissolves gold, which is insoluble in all other acids.

Answer

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

Nitric acid present in aqua regia oxidizes HCl to chlorine.

HNO₃ + 3HCl ⟶ NOCl + 2H₂O + 2[Cl] [nascent chlorine]

This nascent chlorine reacts with noble metals like gold forming the corresponding soluble chloride.

Au + 3[Cl] ⟶ AuCl₃ [Gold (III) Chloride]

Hence, aqua regia dissolves noble metals like gold and platinum which are insoluble in all other acids.

Question 26

Give three tests for hydrochloric acid. Convert silver nitrate to a soluble salt of silver using hydrochloric acid and an alkali.

Answer

(i) When glass rod dipped in ammonia solution (NH₄OH) is brought near vapours of hydrochloric acid, dense white fumes of ammonium chloride are formed.

$\underset{\text{[aq.]}}{\text{NH}_3} + \underset{\text{[vapour]}}{\text{HCl}} \longrightarrow \underset{\text{[dense white fumes]}}{\text{NH}_4\text{Cl}}$

(ii) On addition of silver nitrate soln. to dil. HCl (acidified with dil. HNO₃), curdy white precipitate of silver chloride is obtained.

AgNO₃ + HCl ⟶ AgCl ↓ + HNO₃

(iii) On heating a mixture of manganese dioxide and conc. HCl, Greenish yellow gas (chlorine) is evolved.

MnO₂ + 4HCl ⟶ MnCl₂ ↓ + 2H₂O + Cl₂

Question 27

State two industrial products manufactured from hydrochloric acid, which are also manufactured from nitric and sulphuric acid. Give two general uses of hydrochloric acid.

Answer

Industrial products manufactured from HCl acid are :

1. Dyes
2. Paint

General uses of hydrochloric acid are :

1. Hydrochloric acid dissolves the calcium phosphate present in bones. Hence, it is used in the extraction of glue from bones.
2. Hydrochloric acid dissolves the metallic oxide coating [impurities] on the surface of the metal, thereby cleans the surface. Hence, it is used in pickling of metals before galvanizing.

Unit Test Paper 7A — Hydrogen Chloride

Question 1

Give balanced equations for the conversions A, B, C, D and E given below :

1. $\text{Conc. HCl} \xrightarrow{\text{A}} \text{PbCl}_2 \xleftarrow{\text{B}} \text{dil. HCl}$
2. $\text{NaHCO}_3 \xrightarrow{\text{C}} \text{NaCl} \xrightarrow{\text{D}} \text{NaHSO}_4$
3. $\text{FeCl}_3 \xleftarrow{\text{E}_1} \text{Fe} \xrightarrow{\text{E}_2} \text{FeCl}_2$

Answer

1. A — $4\text{HCl(conc.)} + \text{PbO}_2 \xrightarrow{\Delta} \text{PbCl}_2 + 2\text{H}_2\text{O} + \text{Cl}_2$
   B — $2\text{HCl(dil.)} + \text{Pb(NO}_3)_2 \xrightarrow{\Delta} \text{PbCl}_2 \downarrow + 2\text{HNO}_3$
2. C — NaHCO₃ + HCl ⟶ NaCl + H₂O + CO₂
   D — $\text{NaCl} + \text{H}_2\text{SO}_4 \xrightarrow{\lt 200 \degree\text{C}} \text{NaHSO}_\text{4} + \text{HCl [g]}$
3. E₁ — 2Fe + 3Cl₂ ⟶ 2FeCl₃
   E₂ — Fe + 2HCl [g] ⟶ FeCl₂ + H₂ [g]

Question 2.1

Give reasons for the following :

In the laboratory preparation of HCl acid from NaCl and conc. H₂SO₄, the residual salt formed at temperatures above 200°C forms a hard crust and sticks to the glass.

Answer

At temperatures above 200°C, Sodium sulphate is formed. It forms a hard crust, sticks to the glass and is difficult to remove.

Question 2.2

Give reasons for the following :

Dense white fumes are obtained when a jar of HCl gas is inverted over a jar of ammonia gas.

Answer

When a gas jar containing HCl gas in inverted over a jar full of ammonia gas, dense white fumes are formed. These fumes consists of particles of solid ammonium chloride suspended in air.

NH₃ [g] + HCl [g] ⟶ NH₄Cl (s-solid)

Question 2.3

Give reasons for the following :

In the fountain experiment to demonstrate the high solubility of HCl gas in water, dry HCl gas is filled in the round bottom flask.

Answer

HCl gas present in the flask dissolves in water due to high solubility, creating a partial vacuum in the flask. The outside pressure being higher pushes the blue litmus solution up the jet tube which emerges out at the end of the tube as red fountain. Hence, the inference is that the HCl gas is highly soluble in water and acidic in nature.

Question 2.4

Give reasons for the following :

Iron sheets are cleaned with hydrochloric acid before dipping into molten zinc for galvanizing.

Answer

Hydrochloric acid dissolves the metallic oxide coating [impurities] on the surface of the metal, thereby cleans the metallic surface before galvanizing.

Question 2.5

Give reasons for the following :

Hydrogen chloride gas fumes in moist air but hydrogen sulphide gas does not.

Answer

Due to the high solubility of HCl gas, it fumes in moist air and forms a mist of droplets of HCl acid. On the other hand, Hydrogen Sulphide does not do so as it is slightly soluble in water.

Question 3

Complete the statements given below using the correct word/s

1. An aqueous solution of HCl gas is named ............... [aqua fortis / muriatic acid / oil of vitriol]
2. The salt obtained when rock salt reacts with conc. H₂SO₄ at temperatures below 200°C is a/an ............... [acid/normal] salt.
3. In the preparation of HCl acid from HCl gas, a funnel arrangement provides ............... [less/more] surface area for absorption of the gas.
4. The ions which impart acidic properties to an aqueous solution of hydrogen chloride are ............... [chloride/hydrogen/hydronium]
5. The indicator which does not change colour on passage of hydrogen chloride gas is ............... [moist blue litmus / phenolphthalein / methyl orange].

Answer

1. An aqueous solution of HCl gas is named muriatic acid.
2. The salt obtained when rock salt reacts with conc. H₂SO₄ at temperatures below 200°C is an acid salt.
3. In the preparation of HCl acid from HCl gas, a funnel arrangement provides more surface area for absorption of the gas.
4. The ions which impart acidic properties to an aqueous solution of hydrogen chloride are hydrogen.
5. The indicator which does not change colour on passage of hydrogen chloride gas is phenolphthalein.

Question 4

Choose from the letters A, B, C, D and E, to match the descriptions 1 to 5 given below.

A : NH₄Cl
B : AgCl
C : PbCl₂
D : FeCl₂
E : Ag(NH₃)₂Cl

1. A soluble salt obtained on reaction of a metallic chloride with liquor ammonia.
2. A salt which is insoluble in dilute nitric acid but soluble in ammonium hydroxide.
3. A salt obtained on reaction of an active metal with hydrogen chloride gas.
4. A salt obtained when a basic gas reacts with hydrogen chloride gas.
5. A salt soluble in hot water but not in cold, obtained on heating an oxidising agent with conc. HCl.

Answer

1. A soluble salt obtained on reaction of a metallic chloride with liquor ammonia — E : [Ag(NH₃)₂Cl]
2. A salt which is insoluble in dilute nitric acid but soluble in ammonium hydroxide. — B : AgCl
3. A salt obtained on reaction of an active metal with hydrogen chloride gas. — D : FeCl₂
4. A salt obtained when a basic gas reacts with hydrogen chloride gas. — A : NH₄Cl
5. A salt soluble in hot water but not in cold, obtained on heating an oxidising agent with conc. HCl. — C : PbCl₂

Question 5

Select the correct word or formula from the same given in bracket :

1. The substance reacted with conc. HCl and heated to prove that conc. HCl contains Cl₂. [PbCl₂/PbO₂/PbO]
2. The metal reacted with dil. HCl to prove that dil. HCl contains hydrogen. [Cu/Fe/Ag/Pb]
3. The gas/es which is/are heavier than air and highly soluble in water. [NH₃/HCl/CO₂/H₂S]
4. The acid which is not an oxidizing agent. [Conc. HNO₃ / Conc. HCl / Conc. H₂SO₄]
5. The acid which is not a monobasic acid. [Acetic/Sulphurous/Hydrochloric/Nitric/Formic acid]

Answer

1. The substance reacted with conc. HCl and heated to prove that conc. HCl contains Cl₂. — PbO₂
2. The metal reacted with dil. HCl to prove that dil. HCl contains hydrogen. — Fe
3. The gases which are heavier than air and highly soluble in water. — HCl and NH₃
4. The acid which is not an oxidizing agent. — Conc. HCl
5. The acid which is not a monobasic acid. — Sulphurous acid

Question 6

Select the correct words from the list given below to complete the following word equations :

Metallic oxide, active metal, metallic carbonate, metallic bisulphite, active metal, metallic hydroxide, metallic bicarbonate, metallic sulphate, metallic sulphide.

1. ............... + hydrochloric acid (dil) ⟶ salt + hydrogen
2. ............... + hydrochloric acid (dil) ⟶ salt + water
3. ............... + hydrochloric acid (dil) ⟶ salt + water + carbon dioxide
4. ............... + hydrochloric acid (dil) ⟶ salt + water + sulphur dioxide
5. ............... + hydrochloric acid (dil) ⟶ salt + hydrogen sulphide

Answer

1. Active metal + hydrochloric acid (dil) ⟶ salt + hydrogen
2. Metallic oxide, hydroxide + hydrochloric acid (dil) ⟶ salt + water
3. Metallic carbonate / bicarbonate + hydrochloric acid (dil) ⟶ salt + water + carbon dioxide
4. Metallic bisulphite + hydrochloric acid (dil) ⟶ salt + water + sulphur dioxide
5. Metallic sulphide + hydrochloric acid (dil) ⟶ salt + hydrogen sulphide