Practical Work

(a) Give only one suitable chemical test to identify the following gases.

(i) Ammonia

(ii) Sulphur dioxide

(iii) Hydrogen chloride

(iv) Chlorine

(v) Carbon dioxide

(vi) Oxygen

(vii) Hydrogen

(b) Select a basic gas mentioned in Q. 1(a). How is the basic nature suspected?

(c) Select acidic gases from the gases mentioned in Q. 1 (a). How is the acidic nature suspected?

(d) The two gases A and B are bleaching agents. A is greenish yellow and bleaches due to it's oxidising property while B a colourless gas bleaches due to reduction. Identify A and B.

(e) Which gas turns blue cobalt chloride paper light pink?

Give one similarity in test between (i) Cl₂ and HCl (ii) SO₂ and CO₂.

Answer

(i) Ammonia — When a glass rod dipped in conc. HCl is brought near the gas, dense white fumes of ammonium chloride are formed.

(ii) Sulphur dioxide — Sulphur dioxide gas turns acidified potassium permanganate from pink to clear colourless and acidified potassium dichromate from orange to clear green.

(iii) Hydrogen chloride — Forms a curdy white ppt. on passage through AgNO₃ solution. The precipitate dissolves in excess of NH₄OH.

(iv) Chlorine — Chlorine turns moist blue litmus red and then bleaches it.

(v) Oxygen — Oxygen gas rekindles a glowing wooden splinter.

(iv) Hydrogen — Hydrogen gas burns with a 'pop' sound in air.

(b) Ammonia is a basic gas. It turns red litmus blue.

(c) Sulphur dioxide, Hydrogen chloride, Chlorine, Carbon dioxide.

(d) A is Chlorine and B is Sulphur dioxide.

(e) Water vapour

(i) Similarity in test of Cl₂ and HCl — Forms a white ppt. on reaction with AgNO₃ solution.

(ii) Similarity in test of SO₂ and CO₂ — Both turn lime water milky.

Name the gases which

(a) extinguishes burning wooden splinter.

(b) turns moist red litmus blue.

(c) do no effect on moist litmus.

(d) affect the acidified K₂Cr₂O₇ paper and also turns lime water dirty milky.

Answer

(a) NH₃, HCl, SO₂, H₂S, CO₂, NO₂, Cl₂.

(b) Ammonia [NH₃]

(c) Water vapour, hydrogen, oxygen

(d) sulphur dioxide [SO₂]

Name:

(a) Two carbonates which do not produce carbon dioxide on heating.

(b) A colourless gas which bleaches

(c) Gases which have sour taste

(d) Greenish yellow gas which also bleaches

(e) Gas with rotten egg smell.

Answer

(a) Sodium carbonate [Na₂CO₃] and potassium carbonate [K₂CO₃]

(b) Sulphur dioxide [SO₂]

(c) Carbon dioxide [CO₂]

(d) Chlorine [Cl₂]

(e) Hydrogen sulphide [H₂S]

From the following list of substances choose those which meet the description given below.

1. Ammonium chloride
2. Ammonium nitrate
3. Chlorine
4. Dilute hydrochloric acid
5. Iron
6. Lead nitrate
7. Manganese (IV) oxide
8. Silver nitrate
9. Sodium nitrate
10. Sodium nitrite
11. Sulphur

Two compounds whose aqueous solutions give white precipitates with dilute hydrochloric acid.

Answer

Silver nitrate and Lead nitrate.

HCl + AgNO₃ ⟶ AgCl + HNO₃
2HCl + Pb(NO₃)₂ ⟶ PbCl₂ + 2HNO₃

Name the anion present in each of the following compounds.

(a) Compound A when warmed with concentrated sulphuric acid gives a gas which fumes in moist air and which gives dense white fumes with ammonia.

(b) When barium chloride solution is added to a solution of compound B, a white precipitate insoluble in dilute hydrochloric acid is formed.

(c) The action of heat on the insoluble compound C produces a gas which turns lime water turbid.

(d) Compound D when warmed with dilute sulphuric acid gives a gas which turns acidified dichromate solution green.

Answer

(a) Cl^-

(b) SO₄^2-

(c) CO₃^2-

(d) SO₃^2-

A given white crystalline salt was tested as follows :

(a) It dissolved in water and the resulting solution of the salt turned blue litmus red.

(b) Addition of barium chloride solution into this solution gave a white precipitate.

(c) A flame test on the salt gave a persistent golden-yellow colourisation.

What conclusion can be drawn for each observation?

Answer

(a) As the salt solution turned blue litmus red hence the salt may be an acid.

(b) As white ppt. is obtained on addition of barium chloride so the salt may contain SO₄^2-, SO₃^2-, CO₃^2-.

(c) Persistent golden yellow colourisation which suggests presence of Na⁺ ion.

(a) Sodium hydroxide solution is added to solution A. A white precipitate is formed which is insoluble in excess sodium hydroxide solution. Name the metal ion present in solution A.

(b) When ammonium hydroxide is added to solution B, a pale blue precipitate is formed. This pale blue precipitate dissolves in excess ammonium hydroxide giving an inky blue solution. Name the cation present in solution B.

(c) When an ammonium salt is warmed with sodium hydroxide solution, ammonia gas is evolved. State three ways in which you could identify this gas.

Answer

(a) Ca²⁺

(b) Cu⁺

(c) The three ways to identify ammonia gas are:

1. Ammonia gas turns moist red litmus turns blue.
2. If a glass rod dipped in concentrated HCl is brought near the gas, dense white fumes of ammonium chloride are formed.
3. The gas turns colourless Nessler's reagent i.e. K₂HgI₄ potassium mercuric iodide brown.

Complete the following table and write your observations.

Answer

Use the information given in (a) to (h) to identify the substances P to W selecting your answers from the given list.

(a) P is a white solid. When heated produces white fumes (sublime).

(b) P and R on warming produce an alkaline gas.

(c) On adding water to T, heat is evolved and R is formed.

(d) Q burns brightly in air to form T.

(e) When S is heated, it gives off brown fumes and leaves a black residue of U.

(f) A solution of S is formed by warming U with dilute nitric acid.

(g) V is a gaseous non-metallic element that reacts with hydrogen to form W.

(h) A solution of W will neutralise the solution of R.

Answer

(P) Ammonium chloride

(Q) Calcium

(R) Calcium hydroxide

(S) Lead (II) Nitrate

(T) Calcium Oxide

(U) Lead (II) Oxide

(V) Chlorine

(W) Hydrogen chloride

Copy and complete the following table which refers to the action of heat on some carbonates :

Answer

Distinguish by a chemical test :

(a) Sodium carbonate and sodium sulphite

(b) Sodium chloride and sodium sulphide

(c) Sodium hydroxide solution and ammonium hydroxide solution.

(d) Ammonium sulphate and sodium sulphate.

(e) Sulphuric acid from nitric acid and hydrochloric acid.

Answer

(a) When dil. sulphuric acid is added to sodium carbonate and heated, colourless, odourless gas is evolved which turns lime water milky and has no effect on KMnO₄ or K₂Cr₂O₇ solutions.

When dil. sulphuric acid is added to sodium sulphite and heated, colourless gas with suffocating odour is evolved which turns lime water milky. It turns acidified K₂Cr₂O₇ from orange to clear green and pink coloured KMnO₄ to clear colourless.

Hence, the two compounds can be distinguished.

(b) When dil. sulphuric acid is added to sodium sulphide and heated, hydrogen sulphide gas is evolved which has the smell of rotten eggs and turns lead acetate paper black.
Whereas, when conc. sulphuric acid is added to sodium chloride and heated, HCl gas is evolved which gives dense white fumes when a glass rod dipped in ammonia is brought near it.

(c) When ammonium hydroxide is reacted with a solution of copper sulphate, a pale blue ppt. of copper hydroxide is formed which dissolves in excess of ammonium hydroxide forming a deep blue solution of a soluble complex salt [Cu(NH₃)₄]SO₄ [tetramine copper [II] sulphate] .

CuSO₄ + 2NH₄OH ⟶ (NH₄)₂SO₄ + Cu(OH)₂ ↓

Cu(OH)₂ + (NH₄)₂SO₄ + 2NH₄OH ⟶ [Cu(NH₃)₄]SO₄ + 4H₂O

Whereas, when copper sulphate is added to sodium hydroxide solution, pale blue ppt. of copper hydroxide is obtained which is insoluble in excess of sodium hydroxide.

CuSO₄ + 2NaOH ⟶ Na₂SO₄ + Cu(OH)₂ ↓

(d) When ammonium sulphate is heated with NaOH, ammonia gas is produced which turns red litmus blue whereas, sodium sulphate does not react with sodium hydroxide.

(NH₄)₂SO₄ + 2NaOH ⟶ Na₂SO₄ + 2H₂O + 2NH₃

Na₂SO₄ + NaOH ⟶ no reaction.

(e) Barium chloride reacts with dil H₂SO₄ to form a white ppt. of barium sulphate.

BaCl₂ + H₂SO₄ [dil.] ⟶ 2HCl + BaSO₄ ↓ [white ppt.]

Whereas, HCl and nitric acid does not form a white ppt.

BaCl₂ + HCl ⟶ No white ppt.

BaCl₂ + HNO₃ ⟶ No white ppt

Sodium hydroxide solution is added first in a small quantity, then in excess to the aqueous salt solutions of copper (II) sulphate, zinc nitrate, lead nitrate, calcium chloride and iron (III) sulphate. Copy the following table and write the colour of the precipitate in (i) to (v) and the nature of the precipitate (soluble or insoluble) in (vi) to (x).

Answer

State your observations when:

(a) lead nitrate solution and sodium chloride solution are mixed.

(b) zinc chloride solution, zinc nitrate solution and zinc sulphate solutions are added individually to

(i) barium chloride solution,

(ii) lead nitrate solution.

(c) Decomposition of bicarbonates by dil. H₂SO₄

2NaHCO₃ + H₂SO₄ ⟶ Na₂SO₄ + 2H₂O + 2CO₂

2KHCO₃ + H₂SO₄ ⟶ K₂SO₄ + 2H₂O + 2CO₂

Answer

(a) When lead nitrate solution is mixed with sodium chloride solution, a white precipitate of lead chloride is seen and the soluble salt sodium nitrate is formed.

2NaCl + Pb(NO₃)₂ ⟶ 2Na(NO₃)₂ + PbCl₂↓

Precipitate of lead chloride and sodium nitrate are formed.

(b)

(c) Carbon dioxide gas is evolved with brisk effervescence which turns blue litmus red and extinguishes a burning wooden splinter.

The questions (i) to (v) refer to the following salt solutions listed A to F.

A. Copper nitrate

B. Iron (II) sulphate

C. Iron (III) chloride

D. Lead nitrate

E. Magnesium sulphate

F. Zinc chloride

(i) Which two solutions will give a white precipitate when treated with dilute hydrochloric acid followed by barium chloride solution?

(ii) Which two solutions will give a white precipitate when treated with dilute nitric acid followed by silver nitrate solution?

(iii) Which solution will give a white precipitate, when either dilute hydrochloric acid or dilute sulphuric acid is added to it?

(iv) Which solution becomes a deep/inky blue colour when excess of ammonium hydroxide is added to it?

(v) Which solution gives a white precipitate with excess ammonium hydroxide solution?

Answer

(i) Iron (II) Sulphate and Magnesium sulphate

(ii) Iron (III) chloride and Zinc Chloride

(iii) Lead nitrate

(iv) Copper nitrate.

(v) Lead nitrate.

Mention the colour change when following indicators are added:

Answer

Salts A, B, C, D and E undergo reactions (i) to (v) respectively. Identify the anion present in these salts on the basis of these reactions.

(a) When silver nitrate solution is added to a solution of A, a white precipitate, insoluble in dilute nitric acid, is formed.

(b) Addition of dilute hydrochloric acid to B produces a gas which turns lead acetate paper black.

(c) When a freshly prepared solution of ferrous sulphate is added to a solution of C and concentrated sulphuric acid is gently poured from the side of the test-tube, a brown ring is formed.

(d) When dilute sulphuric acid is added to D, a gas is produced which turns acidified potassium dichromate solution from orange to green.

(e) Addition of dilute hydrochloric acid to E produces an effervescence. The gas produced turns lime water milky but does not affect acidified potassium dichromate solution.

Answer

(a) Chloride ion (Cl^-)

(b) Sulphide ion (S^2-)

(c) Nitrate (NO₃^-)

(d) Sulphite ion (SO₃^2-)

(e) Carbonate ion (CO₃^2-)

(a) The salt which in solution gives a pale green precipitate with sodium hydroxide solution and a white precipitate with barium chloride solution is :

(i) Iron (III) sulphate

(ii) Iron (II) sulphate

(iii) Iron (II) chloride

(iv) Iron (III) chloride

(b) Identify the following substances :

(i) An alkaline gas A which gives dense white fumes with hydrogen chloride.

(ii) Gas C has an offensive smell like rotten eggs.

(iii) Gas D is a colourless gas which can be used as a bleaching agent.

Answer

(a) Iron (II) sulphate

(b) A → Ammonia
     C → Hydrogen sulphide
     D → Sulphur dioxide

Carbon dioxide and sulphur dioxide gas can be distinguished by using

(i) moist blue litmus paper

(ii) lime water

(iii) acidified potassium dichromate paper

(iv) none of the above.

Answer

acidified K₂Cr₂O₇ (potassium dichromate) paper

Reason

There is no effect of CO₂ gas on potassium dichromate whereas SO₂ turns acidified potassium dichromate from orange to clear green.

K₂Cr₂O₇ + H₂SO₄ + 3SO₂ ⟶ K₂SO₄ + Cr₂(SO₄)₃ + H₂O

Identify the substance 'R' based on the information given below :

The pale green solid 'R' turns reddish brown on heating. Its aqueous solution gives a white precipitate with barium chloride solution. The precipitate is insoluble in mineral acids.

Answer

The substance 'R' is Ferrous sulphate (FeSO₄.7H₂O).

Reason

When heated strongly, the hydrous pale green ferrous sulphate (FeSO₄.7H₂O), loses it's water of crystallization and decomposes to form brown ferric oxide Fe₂O₃ along with sulphur dioxide (SO₂) and sulphur trioxide (SO₃).

FeSO₄.7H₂O $\xrightarrow{\Delta}$ FeSO₄ + 7H₂O

2FeSO₄ $\xrightarrow{\Delta}$ Fe₂O₃ + SO₂ + SO₃

Ferrous sulphate on reaction with barium chloride soln., forms a white ppt. of barium sulphate (BaSO₄) which is insoluble in mineral acids.

Give one chemical test to distinguish between the following pairs of compounds.

(i) Zinc sulphate solution and zinc chloride solution

(ii) Iron (II) chloride soln. and iron (III) chloride soln.

(iii) Calcium nitrate soln. and calcium chloride soln.

Answer

(i) When BaCl₂ soln. is added to ZnSO₄, a white ppt. of BaSO₄ is formed, whereas, no ppt. is formed in case of ZnCl₂. Hence, the two solns. can be distinguished.

BaCl₂ + ZnSO₄ ⟶ BaSO₄ ↓ [white ppt.] + ZnCl₂

BaCl₂ + ZnCl₂ ⟶ No white ppt.

(ii) When NaOH soln. is added to the given solns., FeCl₂ reacts to form a dirty green ppt. of Fe(OH)₂ whereas, FeCl₃ reacts to form a reddish brown ppt. of Fe(OH)₃.

(iii) Add silver nitrate soln. to the given solns., calcium chloride reacts to form a white ppt. which is soluble in NH₄OH and insoluble in dil. HNO₃. The other soln. is calcium nitrate.

CaCl₂ + 2AgNO₃ ⟶ 2AgCl ↓ [white ppt.] + Ca(NO₃)₂

Ca(NO₃)₂ + AgNO₃ ⟶ no white ppt.

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

A. Nitroso iron (II) sulphate

B. Iron (III) chloride

C. Chromium sulphate

D. Lead (II) chloride.

(i) The compound which is responsible for the green colour formed when SO₂ is bubbled through acidified potassium dichromate solution.

(ii) Compound responsible for brown ring.

Answer

(i) Chromium sulphate

K₂Cr₂O₇ + H₂SO₄ + 3SO₂ ⟶ K₂SO₄ + Cr₂(SO₄)₃ + H₂O

(ii) Nitroso iron (II) sulphate

State your observation :

(i) a piece of moist blue litmus paper (ii) paper soaked in potassium permanganate solution — is introduced in each case into ajar of sulphur dioxide.

Answer

(i) Moist blue litmus turns red.

(ii) Sulphur dioxide turns potassium permanganate from pink to clear colourless.

2KMnO₄ + 2H₂O + 5SO₂ ⟶ K₂SO₄ + 2MnSO₄ + 2H₂SO₄

Write the equation for the reaction of magnesium sulphate solution with barium chloride solution.

Answer

MgSO₄ + BaCl₂ ⟶ BaSO₄ ↓ [white ppt.] + MgCl₂

Choose from the list of substances — Acetylene gas, aqua fortis, coke, brass, barium chloride, bronze, platinum.

An aqueous salt solution used for testing sulphate radical.

Answer

Barium chloride.

Name — the gas which turns acidified potassium dichromate solution green.

Answer

Sulphur dioxide gas (SO₂)

Identify the anion present in the following compounds :

(i) Compound X on heating with copper turnings and conc. sulphuric acid liberates a reddish brown gas.

(ii) When a solution of compound Y is treated with silver nitrate solution a white precipitate is obtained which is soluble in excess of ammonium hydroxide solution.

(iii) Compound Z which on reacting with dilute sulphuric acid liberates a gas which turns lime water milky, but the gas has no effect on acidified potassium dichromate solution.

(iv) Compound L on reacting with barium chloride solution gives a white precipitate insoluble in dilute hydrochloric acid or dilute nitric acid.

Answer

(i) Nitrate ion, NO₃^-

(ii) Chloride ion, Cl^-

(iii) Carbonate ion, CO₃^2-

(iv) Sulphate ion, SO₄^2-

State one chemical test between each of the following pairs :

(i) Sodium carbonate and sodium sulphite.

(ii) Ferrous nitrate and lead nitrate.

(iii) Manganese dioxide and copper (Il) oxide.

Answer

(i) When dil. sulphuric acid is added to sodium carbonate and heated, colourless, odourless gas is evolved which turns lime water milky and has no effect on KMnO₄ or K₂Cr₂O₇ solutions.

When dil. sulphuric acid is added to sodium sulphite and heated, colourless gas with suffocating odour is evolved which turns lime water milky. It turns acidified K₂Cr₂O₇ from orange to clear green and pink coloured KMnO₄ to clear colourless.

Hence, the two compounds can be distinguished.

(ii) When NaOH is added to each of the compounds, a dirty green precipitate of Iron [II] hydroxide [Fe(OH)₂] is formed in case of Ferrous nitrate whereas a chalky white precipitate of lead hydroxide [Pb(OH)₂] is formed in case of lead nitrate. Iron [II] Hydroxide [Fe(OH)₂] is insoluble in excess of NaOH, whereas Lead Hydroxide [Pb(OH)₂] is soluble in excess of NaOH. Hence, the two compounds can be distinguished.

(iii) When each of the compound is heated with conc. hydrochloric acid, greenish yellow (chlorine) gas is evolved in case of manganese dioxide and filtrate is brownish in colour whereas, no chlorine gas is evolved in case of copper (II) oxide and filtrate is bluish in colour.

MnO₂ + 4HCl ⟶ MnCl₂ + 2H₂O + Cl₂

CuO + 2HCl ⟶ CuCl₂ + H₂O

Give a chemical test to distinguish between :

(i) Sodium chloride soln. and sodium nitrate soln.

(ii) Hydrogen chloride gas and hydrogen sulphide gas.

(iii) Calcium nitrate soln. and zinc nitrate soln.

(iv) Carbon dioxide gas and sulphur dioxide gas.

Answer

(i) Add silver nitrate soln. to the given solns., sodium chloride reacts to form a white ppt. which is soluble in NH₄OH and insoluble in dil. HNO₃. The other soln. is sodium nitrate.

NaCl + AgNO₃ ⟶ AgCl ↓ [white ppt.] + NaNO₃

NaNO₃ + AgNO₃ ⟶ no white ppt.

(ii) Hydrogen sulphide gas turns moist lead acetate paper silvery black or black whereas, no change is observed in case of HCl gas.

Pb(CH₃COO)₂ [colourless] + H₂S ⟶ PbS [black] + 2CH₃COOH

(iii) When NaOH is added to the given soln., Zn(NO₃)₂ reacts to form a gelatinous white ppt. which dissolves in excess of NaOH whereas, Ca(NO₃)₂ forms a milky white ppt. which is insoluble in excess of NaOH. Hence, the two can be distinguished.

(iv) Carbon dioxide gas has no effect on acidified potassium permanganate (KMnO₄) and acidified potassium dichromate (K₂Cr₂O₇) solution whereas sulphur dioxide gas turns acidified potassium permanganate from pink to clear colourless and acidified potassium dichromate from orange to clear green.

2KMnO₄ + 2H₂O + 5SO₂ ⟶ K₂SO₄ + 2MnSO₄ + 2H₂SO₄

K₂Cr₂O₇ + H₂SO₄ + 3SO₂ ⟶ K₂SO₄ + Cr₂(SO₄)₃ + H₂O

Distinguish between : Sodium nitrate and sodium sulphite [using dilute sulphuric acid].

Answer

Sodium nitrate will not react with dilute sulphuric acid.

Sodium sulphite reacts with dil. sulphuric acid and colourless gas with suffocating odour is evolved which turns lime water milky.

State your observation : When moist starch iodide paper is introduced into chlorine gas.

Answer

Chlorine gas turns moist starch iodide paper blue black.

Cl₂ + 2KI ⟶ 2KCl + I₂
[Starch + I₂ ⟶ blue black colour]

The flame test with a salt P gave a brick red flame. What is the cation in P.

Answer

Cation in P is Ca²⁺ (calcium ion).

A gas Q turns moist lead acetate paper silvery black. Identify the gas Q.

Answer

The gas Q is H₂S (Hydrogen sulphide).

Pb(CH₃COO)₂ [colourless] + H₂S ⟶ PbS [black] + 2CH₃COOH

pH of liquid R is 10. What kind of substance is R ?

Answer

R is an alkaline substance.