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Chapter 9

Practical Chemistry

Class 10 - Dalal Simplified ICSE Chemistry Solutions



Questions

Question 1(2006)

From the list of substances given — Ammonium sulphate, Lead carbonate, Chlorine, Copper nitrate, Ferrous sulphate — State : A substance that turns moist starch iodide paper blue.

Answer

Chlorine

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

Question 2(2006)

State what is observed when excess of ammonia passed through an aqueous solution of lead nitrate.

Answer

Chalky white precipitate of lead hydroxide is formed which is insoluble in excess of ammonia.

Pb(NO3)2 + 2NH4OH ⟶ 2NH4NO3 + Pb(OH)2 ↓ [Chalky white ppt. formed]

Question 3(2006)

Give one test each to distinguish between the following pairs of chemical solutions

(i) Zn(NO3)2 and Ca(NO3)2

(ii) NaNO3 and NaCl

(iii) Iron [III] chloride and copper chloride .

Answer

(i) 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.

(ii) Add conc. sulphuric acid to the given salts, NaCl will react to produce HCl gas, which produces dense white fumes when a glass rod dipped in ammonia soln. is brought near it. If we add copper turnings along with conc. sulphuric acid, NaNO3 will react to give reddish brown nitrogen dioxide. Hence, the two salts can be distinguished.

(iii) When we add NaOH solution to the given solutions, Iron [III] chloride forms a reddish brown ppt. of Fe(OH)3 whereas, copper chloride gives a pale blue ppt of Cu(OH)2.

Question 4(2006)

Give a reason why carbon dioxide and sulphur dioxide cannot be distinguished by using lime water.

Answer

Both, carbon dioxide and sulphur dioxide turns lime water milky due to the formation of CaCO3 and CaSO3, respectively. Hence, lime water cannot be used to distinguish between the two.

Ca(OH)2 + CO2 ⟶ CaCO3 ↓ [white ppt. - insoluble] + H2O

Ca(OH)2 + SO2 ⟶ CaSO3 ↓ [white ppt. - insoluble] + H2O

Question 1(2007)

Salts A, B, C, D and E undergo reactions (i) to (v) respectively. Identify the anion present in each salt.

(i) When AgNO3 solution is added to a soln. of A, a white precipitate, insoluble in dilute nitric acid, is formed.

(ii) Addition of dil. HCl to B produces a gas which turns lead acetate paper black.

(iii) When a freshly prepared solution of FeSO4 is added to a soln. of C and conc. H2SO4 is gently poured from the side of the test-tube, a brown ring is formed.

(iv) When dil. H2SO4 is added to D a gas is produced which turns acidified K2Cr2O7 soln. from orange to green.

(v) Addition of dil. HCl to E produced an effervescence. The gas produced turns limewater milky but does not effect acidified K2Cr2O7 soln.

Answer

(i) Chloride (Cl1-)

(ii) Sulphide (S2-)

(iii) Nitrate (NO31-)

(iv) Sulphite (SO32-)

(v) Carbonate (CO32-)

Question 2(2007)

How will the addition of barium chloride soln. help to distinguish between dil. HCl and dil. H2SO4.

Answer

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

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

Whereas, dil. HCl does not form a white ppt. Hence, the two can be distinguished.

BaCl2 + HCl [dil.] ⟶ No white ppt.

Question 1(2008)

The salt which in solution gives a pale green ppt. with NaOH soln. and a white ppt. with barium chloride solution is :

  1. Iron (III) sulphate
  2. Iron (II) sulphate
  3. Iron (II) chloride
  4. Iron (III) chloride

Answer

Iron (II) sulphate

Pale green ppt. of Fe(OH)2 and white ppt. of barium sulphate are formed.

Question 1(2009)

CO2 and SO2 gas can be distinguished using :

  1. moist blue litmus paper
  2. lime water
  3. acidified K2Cr2O7 paper
  4. 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

Question 2(2009)

Identity the substance 'R' based on the information given below : The pale green solid 'R' turns reddish brown on heating. It's 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 Δ\xrightarrow{\Delta} FeSO4 + 7H2O

2FeSO4 Δ\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.

Question 3(2009)

Give one test each to distinguish between the following pairs of chemical solutions:

(i) ZnSO4 and ZnCl2

(ii) FeCl2 and FeCl3

(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.

Question 1(2010)

Select the correct answer from A, B, C, D and E –

(A) : Nitroso Iron (II) sulphate

(B) : Iron (III) chloride

(C) : Chromium sulphate

(D) : Lead (II) chloride

(E) : Sodium chloride.

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

Answer

Chromium sulphate

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

Question 2(2010)

State your observation – (i) A piece of moist blue litmus paper (ii) paper soaked in potassium permanganate solution - is introduced in each case into a jar 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

Question 3(2010)

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

Answer

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

Question 1 (2011)

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.

Question 1(2012)

Name the gas which turns acidified potassium dichromate clear green.

Answer

Sulphur dioxide gas (SO2)

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

Question 2(2012)

Identify the anion present in the following compounds :

(i) Compound X on heating with copper turnings and concentrated 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, CO32-

(iv) Sulphate ion, SO42-

Question 3(2012)

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 (II) 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

Question 4(2012)

State one observation : A zinc granule is added to copper sulphate solution.

Answer

Zinc displaces copper from copper sulphate and forms zinc sulphate soln. because zinc is more reactive than copper. Hence, the blue colour of copper sulphate solution changes to colourless.

Question 5(2012)

Give balanced equation for the reaction :

Silver nitrate solution and Sodium chloride solution.

Answer

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

Question 1(2013)

Give a chemical test to distinguish between :

(i) NaCl soln. and NaNO3 soln.

(ii) HCl gas and H2S 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

Question 2(2013)

From

A : CO
B : CO2
C : NO2
D : SO3

State which will not produce an acid on reaction with water.

Answer

CO
Reason — On reaction with water, CO2 produces carbonic acid, NO2 forms nitric acid and SO3 forms sulphuric acid whereas CO forms carbon dioxide gas.

CO + H2O ⟶ CO2 + H2

Question 1(2014)

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.

Question 2(2014)

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]

Question 3(2014)

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).

Question 4(2014)

Gas Q turns moist lead acetate paper silvery black. Identify Q. pH of R is 10. What kind of substance is R?

Answer

The gas Q is H2S (Hydrogen sulphide).

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

R is an alkaline substance.

Question 1(2015)

Select the gas that has a characteristic rotten egg smell. [ammonia, ethane, hydrogen chloride, hydrogen sulphide, ethyne]

Answer

Hydrogen sulphide

Question 2(2015)

State one relevant observation : When hydrogen sulphide gas is passed through lead acetate solution.

Answer

A silvery black precipitate of PbS is formed.

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

Question 3(2015)

Identify the anion present in each of the following compounds: A, B, C :

(i) Salt 'A' reacts with conc. H2SO4 producing a gas which fumes in moist air and gives dense fumes with ammonia.

(ii) Salt 'B' reacts with dil. H2SO4 producing a gas which turns lime water milky but has no effect on acidified potassium dichromate solution.

(iii) When barium chloride solution is added to salt solution. 'C' a white precipitate insoluble in dilute hydrochloric acid is obtained.

Answer

(i) Chloride ion (Cl)

(ii) Carbonate ion (CO32–)

(iii) Sulphate ion (SO42–)

Question 4(2015)

Identify the cation present in each of the following compounds — W, X, Y, Z :

(i) To solution 'W', ammonium hydroxide is added in minimum quantity first and then in excess. A dirty white precipitate is formed which dissolves in excess to form a clear solution.

(ii) To solution 'X' ammonium hydroxide is added in minimum quantity first and then in excess. A pale blue precipitate is formed which dissolves in excess to form a clear inky blue solution.

(iii) To solution 'Y' a small amount of sodium hydroxide is added slowly and then in excess. A white insoluble precipitate is formed.

(iv) To salt 'Z' - Ca(OH)2 soln. is added and heated. A pungent smelling gas turning moist red litmus paper blue is obtained.

Answer

(i) Zn2+ (Zinc Ion)

ZnSO4 + 2NH4OH ⟶ (NH4)2SO4 + Zn(OH)2

Zn(OH)2 + (NH4)2SO4 + 2NH4OH [in excess] ⟶ 4H2O + [Zn(NH3)4]SO4

(ii) Cu2+ (Copper (II) Ion)

CuSO4 + 2NH4OH ⟶ (NH4)2SO4 + Cu(OH)2

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

(iii) Ca2+ (Calcium Ion)

CaCl2 + 2NaOH ⟶ 2NaCl + Ca(OH)2

(iv) NH4+ (Ammonium Ion)

2NH4Cl + Ca(OH)2 ⟶ CaCl2 + 2H2O + 2NH3

Question 1(2016)

Identify the cations in each of the following cases :

(i) NaOH solution when added to the solution 'A' - gives a reddish brown precipitate.

(ii) NH4OH solution when added to the solution 'B' - gives a white ppt which does not dissolve in excess.

(iii) NaOH solution when added to the solution 'C' - gives a white ppt which is insoluble in excess.

Answer

(i) Ferric (Fe3+) ion

(ii) Lead (Pb2+) ion

(iii) Calcium (Ca2+) ion

Question 1(2017)

Choose the correct answer from the options – A chloride which forms a precipitate that is soluble in excess of ammonium hydroxide, is :

  1. Calcium chloride
  2. Ferrous chloride
  3. Ferric chloride
  4. Copper chloride.

Answer

Copper chloride.

Question 2(2017)

Identify the substance underlined – Cation that does not form a precipitate with ammonium hydroxide but forms one with sodium hydroxide.

Answer

Calcium [Ca2+] ions

Question 3(2017)

Identify the salts P and Q from the observations given below :

(i) On performing the flame test salt P produces a lilac coloured flame and it's solution gives a white precipitate with silver nitrate solution, which is soluble in ammonium hydroxide solution.

(ii) When dilute HCl is added to a salt Q, a brisk effervescence is produced and the gas turns lime water milky. When NH4OH solution is added to the above mixture [after adding dilute HCl], it produces a white precipitate which is soluble in excess NH4OH solution.

Answer

(i) P is potassium chloride.

Reason — K+ ions produces lilac coloured flame and Cl- ions react with silver nitrate to form silver chloride ppt. (soluble in excess of ammonium hydroxide).

(ii) Q is zinc carbonate.

Reason — CO32- ions produces carbon dioxide with HCl. Zinc chloride forms white ppt. with ammonium hydroxide ( soluble in excess of ammonium hydroxide).

Question 1(2018)

State one relevant observation - Barium chloride solution is slowly added to sodium sulphate solution.

Answer

A white ppt. is obtained which is insoluble in dil. HCl or dil. HNO3

Na2SO4 + BaCl2 ⟶ BaSO4 ↓ [white ppt.] + 2NaCl

BaSO4 is insoluble in dil. hydrochloric acid.

Question 2(2018)

Give a chemical test to distinguish between following pairs of chemicals :

(i) Lead nitrate solution and zinc nitrate solution.

(ii) Sodium chloride solution and sodium nitrate solution

Answer

(i) When NaOH is added to each of the compounds, lead nitrate forms a chalky white precipitate of lead hydroxide [Pb(OH)2] whereas a gelatinous white precipitate of zinc hydroxide [Zn(OH)2] is formed in case of zinc nitrate.

(ii) 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 + NaNO3

NaNO3 + AgNO3 ⟶ no white ppt.

Question 1(2019)

State one observation for the following : Lead nitrate is heated strongly in a test tube.

Answer

White crystalline solid turns buff yellow on heating, gives crackling sound, melts and fuses with the glass. Nitrogen dioxide (reddish brown) and Oxygen (colourless) gases are evolved.

2Pb(NO3)2[lead nitrate (white)]Δ2PbO[litharge - buff yellow]+4NO2[Nitrogen dioxide]+O2[Oxygen]\underset{\text{[lead nitrate (white)]}}{2\text{Pb(NO}_3)_2} \overset{\Delta}{\longrightarrow} \underset{\text{[litharge - buff yellow]}}{2\text{PbO}} + \underset{\text{[Nitrogen dioxide]}}{4\text{NO}_2} + \underset{\text{[Oxygen]}}{\text{O}_2}

Question 2(2019)

Distinguish between the following pairs of compounds using the reagent given in the bracket.

(i) Manganese dioxide and copper [II] oxide [using conc. HCl]

(ii) Ferrous sulphate solution and ferric sulphate solution [using sodium hydroxide solution]

Answer

(i) 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

(ii) When sodium hydroxide is added to the two solns., ferrous sulphate solution gives a dirty green ppt. of Fe(OH)2 whereas, ferric sulphate solution forms a reddish brown ppt. of Fe(OH)3. Hence, the two compounds can be distinguished.

Question 1(2020)

State one relevant observation for the following reaction : Zinc carbonate is heated strongly.

Answer

The original white colour turns yellow on heating. Colourless, odourless carbon dioxide gas is evolved.

ZnCO3ZnO+CO2[Zinc[Zinc oxide][Carboncarbonate][yellow - hot]dioxide][white][white - cold]\begin{matrix} \text{ZnCO}_3 &\longrightarrow & \text{ZnO} & + & \text{CO}_2 \\ \text{[Zinc} & & \text{[Zinc oxide]} & & \text{[Carbon} \\ \text{carbonate]} & & \text{[yellow - hot]} & & \text{dioxide]} \\ \text{[white]} & & \text{[white - cold]} \end{matrix}

Question 2(2020)

State one relevant reason for the following : Hydrated copper sulphate crystals turn white on heating.

Answer

The blue coloured hydrous copper sulphate changes to white anhydrous copper sulphate as the water of crystallization is removed on heating.

CuSO4.5H2O ⟶ CuSO4 + 5H2O

Question 3(2020)

Match the gases given in column I to the identification of the gases mentioned in column II

Column IColumn II
(i) Hydrogen sulphideA : Turns acidified potassium dichromate solution green
(ii) Carbon dioxideB: Turns lime water milky
(iii) Sulphur dioxideC: Turns reddish brown when it reacts with oxygen
   D: Turns moist lead acetate paper silvery black.

Answer

Column IColumn II
(i) Hydrogen sulphideD: Turns moist lead acetate paper silvery black.
(ii) Carbon dioxideB: Turns lime water milky
(iii) Sulphur dioxideA : Turns acidified potassium dichromate solution green

Question 4(2020)

Distinguish between the following pairs of compounds using a reagent as a chemical test:

(i) Calcium nitrate and Zinc nitrate solution

(ii) Magnesium chloride and Magnesium nitrate solution

Answer

(i) When NaOH is added to the given soln., Zinc nitrate [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.

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

MgCl2 + 2AgNO3 ⟶ 2AgCl ↓ [white ppt.] + Mg(NO3)2

Mg(NO3)2 + AgNO3 ⟶ no white ppt.

Question 5(2020)

Identify the salts P, Q, R from the following observations:

(i) Salt P has light bluish green colour. On heating, it produces a black coloured residue. Salt P produces brisk effervescence with dil. HCl and the gas evolved turns lime water milky, but no action with acidified potassium dichromate solution.

(ii) Salt Q is white in colour. On strong heating, it produces buff yellow residue and liberates reddish brown gas. Solution of salt Q produces chalky white insoluble ppt. with excess of ammonium hydroxide.

(iii) Salt R is black in colour. On reacting with conc. HCl, it liberates a pungent greenish yellow gas which turns moist starch iodide paper blue black.

Answer

(i) Copper carbonate

(ii) Lead nitrate

(iii) Manganese dioxide

Additional Questions

Question 1

The following materials are provided – solutions of cobalt chloride, ammonia, potassium permanganate, lime water, starch-iodide, sodium hydroxide, lead acetate, potassium iodide. Also provided are litmus and filter papers, glowing splinters and glass rods. Using the above how would you distinguish between :

(a) a neutral, acidic and a basic gas

(b) oxygen and hydrogen gas

(c) carbon dioxide and sulphur dioxide gas

(d) chlorine and hydrogen chloride gas

(e) hydrogen sulphide and nitrogen dioxide gas

(f) ammonia and carbon dioxide gas

(g) zinc carbonate and potassium nitrate

(h) hydrated copper sulphate and anhydrous copper sulphate

(i) ammonium sulphate and sodium sulphate.

Answer

(a) Litmus paper test is done to distinguish between neutral, acidic and basic gas. Neutral gas does not effect litmus paper. Acidic gas will turn blue litmus paper red and basic gas will turn red litmus blue.

(b) A burning wooden splinter is extinguished in hydrogen whereas oxygen gas rekindles a glowing wooden splinter. Hence, the two gases can be distinguished using a wooden splinter.

(c) There is no effect of carbon dioxide (CO2) gas on potassium permanganate soln. whereas sulphur dioxide (SO2) turns acidified potassium permanganate from pink to clear colourless.

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

Cl2 + H2O ⟶ HOCl + HCl

HOCl ⟶ HCl + [O]

Colouring matter + [O] ⟶ Colourless or bleached product.

Whereas, HCl gas only turns moist blue litmus paper red and does not bleach it.

(e) Nitrogen dioxide (NO2) liberates iodine [violet vapours] with potassium iodide KI soln., and turns potassium iodide paper brown.

2KI + 2NO2 ⟶ 2KNO2 + I2

Hydrogen sulphide (H2S) gas turns potassium permanganate (KMnO4) from pink to colourless.

2KMnO4 + 3H2SO4 + 5H2S ⟶ K2SO4 + 2MnSO4 + 8H2O + 5S

(f) In the presence of ammonia moist red litmus turns blue and carbon dioxide turns moist blue litmus faint red.

(g) If we heat the given salts, zinc carbonate turns yellow, evolving carbon dioxide gas which turns lime water milky and has no effect on potassium permanganate solution.

ZnCO3ΔZnO+CO2[Zinc[Zinc oxide][Carboncarbonate][yellow - hot]dioxide][white][white - cold]\begin{matrix} \text{ZnCO}_3 &\xrightarrow\Delta & \text{ZnO} & + & \text{CO}_2 \\ \text{[Zinc} & & \text{[Zinc oxide]} & & \text{[Carbon} \\ \text{carbonate]} & & \text{[yellow - hot]} & & \text{dioxide]} \\ \text{[white]} & & \text{[white - cold]} \end{matrix}

Whereas, potassium nitrate emits oxygen gas on heating. Oxygen gas rekindles a glowing wooden splinter.

2KNO3 ⟶ 2KNO2 + O2

Hence, the two salts can be distinguished.

(h) Hydrated copper sulphate is bright blue in colour, whereas anhydrous copper sulphate appears as a white powder. Hence, the two can be distinguished by their colour and appearance.

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

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

Na2SO4 + NaOH ⟶ no reaction.

Question 2

Give a chemical test to distinguish between the following:

(i) Sodium carbonate and sodium sulphate

(ii) Potassium chloride and potassium nitrate

(iii) Copper carbonate and copper sulphite

(iv) Lead chloride and lead sulphide

(v) Iron (II) sulphate and iron (III) sulphate

(vi) Calcium sulphate and zinc sulphate

(vii) Lead nitrate and zinc nitrate

(viii) Copper sulphate and calcium sulphate

(ix) Manganese dioxide and copper (II) oxide

(x) dil. HCl, dil. HNO3, dil. H2SO4.

[explain the procedure for the preparation of the solutions for the above tests wherever required]

Answer

(i) When BaCl2 solution is added to sodium carbonate, a white ppt. is formed which is soluble in dil. HCl.

Na2CO3 + BaCl2 ⟶ BaCO3 ↓ [white ppt.] + 2NaCl

BaCO3 + 2HCl ⟶ BaCl2 [soluble] + H2O + CO2

When BaCl2 solution is added to sodium sulphate, a white ppt. is formed which is insoluble in dil. HCl.

Na2SO4 + BaCl2 ⟶ BaSO4 ↓ [white ppt.] + 2NaCl

Hence, the two compound can be distinguished.

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

KCl + AgNO3 ⟶ AgCl + KNO3

KNO3 + AgNO3 ⟶ no white ppt.

(iii) Add dil. H2SO4 to both the solns. and heat. When a colourless, odourless gas is evolved which has no effect on acidified KMnO4 or K2Cr2O7 solns., then the gas is carbon dioxide and the compound is copper carbonate.

When a colourless gas with a suffocating odour is evolved which turns pink acidified KMnO4 to colourless then the gas is sulphur dioxide and the compound is copper sulphite.

(iv) Add dil. H2SO4 to both the solns. and heat. When a colourless gas with a smell of rotten eggs is evolved which turns pink acidified KMnO4 colourless, then the gas is hydrogen sulphide and the compound is lead sulphide.

Now, add conc. H2SO4 to both the solns. and heat. When a gas with a pungent smell is evolved, which gives dense white fumes when a rod dipped in ammonia soln. is brought near it then the gas is HCl and compound is lead chloride.

(v) When sodium hydroxide is added to the two solns., Iron (II) sulphate solution gives a dirty green ppt. of Fe(OH)2 whereas, Iron (III) sulphate solution forms a reddish brown ppt. of Fe(OH)3. Hence, the two compounds can be distinguished.

(vi) When NaOH is added to the given soln., zinc sulphate reacts to form a gelatinous white ppt. which dissolves in excess of NaOH.

ZnSO4 + 2NaOH ⟶ Na2SO4 + Zn(OH)2

Zn(OH)2 + 2NaOH [excess] ⟶ 2H2O + Na2ZnO2

Whereas, calcium sulphate forms a milky white ppt. which is insoluble in excess of NaOH. Hence, the two can be distinguished.

CaSO4 + 2NaOH ⟶ Ca(OH)2 ↓ + Na2SO4

(vii) When NaOH is added to each of the compounds, lead nitrate forms a chalky white precipitate of lead hydroxide [Pb(OH)2]

Pb(NO3)2 + 2NaOH ⟶ 2NaNO3 + Pb(OH)2

Whereas a gelatinous white precipitate of zinc hydroxide [Zn(OH)2] is formed in case of zinc nitrate.

Zn(NO3)2 + 2NaOH ⟶ 2NaNO3 + Zn(OH)2

(viii) When NaOH is added to each of the compounds, copper sulphate forms a pale blue precipitate of copper [II] hydroxide [Cu(OH)2]

CuSO4 + 2NaOH ⟶ Na2SO4 + Cu(OH)2

Whereas a milky white precipitate of calcium hydroxide [Ca(OH)2] is formed in case of calcium sulphate.

CaSO4 + 2NaOH ⟶ Na2SO4 + Ca(OH)2

(ix) 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

(x) When BaCl2 is added to the three acids, dil sulphuric acid reacts with BaCl2 to give a white ppt. of BaSO4 but with dil HCl and dil HNO3 no white ppt. is produced.

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

To distinguish between dil HCl and dil HNO3, we add Silver Nitrate (AgNO3) solution to the two acids. Dil. HCl reacts with AgNO3 to give a curdy white ppt. of Silver chloride (AgCl) but with dil HNO3, no white ppt. is produced.

HCl + AgNO3 ⟶ AgCl + HNO3

HNO3 + AgNO3 ⟶ no white ppt.

Hence, the acids can be distinguished.

Question 3

Identify the cation [positive ion] and anion [negative ion] in - A, B and C. Also identify P, Q, R, S, T, U, V, W.

(a) Substance 'A' is water soluble and gives a curdy white precipitate 'P' with silver nitrate solution. 'P' is soluble in ammonium hydroxide but insoluble in dil. HNO3. Substance 'A' reacts with ammonium hydroxide solution to give a white precipitate 'Q' soluble in excess of NH4OH.

(b) A solution of substance 'B' is added to barium chloride solution. A white ppt. 'R' is formed, insoluble in dil. HCl or HNO3. A dirty green ppt. 'S' is formed on addition of ammonium hydroxide to a solution of 'B' and the precipitate is insoluble in excess of ammonium hydroxide.

(c) Substance 'C' is a coloured, crystalline salt which on heating decomposes leaving a black residue 'T'. On addition of copper turnings and conc. H2SO4 to 'C' a coloured acidic gas 'U' is evolved on heating. A solution of 'C' is added to NaOH soln. until in excess. A pale blue ppt. 'P' is obtained insoluble in excess of NaOH. A solution of 'C' is then added to NH4OH soln. in excess to give an inky blue solution 'V'. A solution of 'C' is warmed and hydrogen sulphide gas is passed through it. A black ppt. 'W' appears.

Answer

(a) A is ZnCl2

Cation and anion in ZnCl2 : Zn2+ and Cl-

ZnCl2 + 2AgNO3 ⟶ 2AgCl ↓ [curdy white ppt.] + Zn(NO3)2

P is AgCl

The precipitate AgCl is soluble in ammonium hydroxide but insoluble in dil. HNO3.

ZnCl2 + 2NH4OH ⟶ 2NH4Cl + Zn(OH)2 ↓ [white ppt.]

2NH4Cl + Zn(OH)2 + 2NH4OH [excess] ⟶ 4H2O + [Zn(NH3)2]Cl2

Q is Zn(OH)2

(b) B is ferrous sulphate (FeSO4)

Cation and anion in FeSO4 : Fe2+ and SO42-

FeSO4 + BaCl2 ⟶ BaSO4 ↓ [white ppt.] + 2NaCl

R is BaSO4

FeSO4 + 2NH4OH ⟶ (NH4)2SO4 + Fe(OH)2

S is Fe(OH)2

(c) C is copper nitrate Cu(NO3)2

Cation and anion in Cu(NO3)2 : Cu2+ and NO31-

Black residue (T) : CuO - copper oxide

2Cu(NO3)2[Copper nitrate (blue)]Δ2CuO[copper oxide - black]+4NO2[Nitrogen dioxide]+O2[Oxygen]\underset{\text{[Copper nitrate (blue)]}}{2\text{Cu(NO}_3)_2} \overset{\Delta}{\longrightarrow} \underset{\text{[copper oxide - black]}}{2\text{CuO}} + \underset{\text{[Nitrogen dioxide]}}{4\text{NO}_2} + \underset{\text{[Oxygen]}}{\text{O}_2}

U is Nitrogen dioxide (NO2)

P is Copper [II] hydroxide Cu(OH)2

Cu(NO3)2 + 2NaOH ⟶ 2NaNO3 + Cu(OH)2

V is [Cu(NH3)4]SO4

Cu(NO3)2 + 2NH4OH ⟶ Cu(OH)2 ↓ + 2NH4NO3

2Cu(OH)2 + 2NH4NO3 + 2NH4OH ⟶ 2Cu(NH3)4NO3 + 4H2O

W is CuS

Cu(NO3)2 + H2S ⟶ CuS + 2HNO3

Unit Test Paper — Chemistry Practicals

Question 1

Match the 'cations' A to F and the solubility of ppt. G or H with the correct colours from 'X' and 'Y'.

'X' on addition of NaOH in excessCationSolubility of ppt. in excess'Y' on addition of NH4OH in excessCationSolubility of ppt. in excess
1. Reddish brown ppt.A: Ca2+G: Soluble6. Dirty green ppt.A: Ca2+G: Soluble
2. Pale blue ppt.B: Zn2+H: Insoluble7. No ppt. formedB: Zn2+H: Insoluble
3. Gelatinous white ppt.C: Fe2+  8. Gelatinous white ppt.C: Fe2+
4. Chalky white ppt.D: Cu2+  9. Pale blue ppt.D: Cu2+
5. Milky white ppt.E: Pb2+  10. Chalky white ppt.E: Pb2+
  F: Fe3+    F: Fe3+

Answer

'X' on addition of NaOH:

CationIn small amt (ppt. formed)solubility of ppt. in excess
A: Ca2+Milky white ppt.Insoluble
B: Zn2+Gelatinous white ppt.Soluble
C: Fe2+Dirty green ppt.Insoluble
D: Cu2+Pale blue ppt.Insoluble
E: Pb2+Chalky white ppt.Soluble
F: Fe3+Reddish brown ppt.Insoluble

'Y' on addition of NH4OH:

CationIn small amt (ppt. formed)solubility of ppt. in excess
A: Ca2+No ppt. formed-
B: Zn2+Gelatinous white ppt.Soluble
C: Fe2+Dirty green ppt.Insoluble
D: Cu2+Pale blue ppt.Soluble
E: Pb2+Chalky white ppt.Insoluble
F: Fe3+Reddish brown ppt.Insoluble

Question 2

Select the correct 'anion' of a salt from the anions given, which matches with description 1 to 5.

A: CO32-, B: NO31-, C: SO42-, D: Cl-, E: S2-

  1. The salt soln. reacts with AgNO3 soln. to give a white ppt. insoluble in dil. HNO3.
  2. The salt soln. reacts with Ba(NO3)2 soln. to give a white ppt. insoluble in dil. HNO3.
  3. The salt soln. reacts with Ba(NO3)2 soln. to give a white ppt. soluble in dil. HNO3 but insoluble in dil. H2SO4.
  4. The salt reacts with dil. H2SO4 on heating evolving a gas which turns KMnO4 soln. pink to colourless.
  5. The salt reacts with conc. H2SO4 on heating evolving a coloured gas which turns potassium iodide paper brown.

Answer

  1. D: Cl-
  2. C: SO42-
  3. A: CO32-
  4. E: S2-
  5. B: NO31-

Question 3

Give balanced equations for the conversions A and B.

  1. Metallic carbonateA Ba(NO3)2White precipitateB dil. HClprecipitate dissolves\text{Metallic carbonate} \quad \raisebox{0.35em}{A} \space \xrightarrow{\text{Ba(NO}_3)_2} \text{White precipitate} \quad \raisebox{0.35em}{B} \space \xrightarrow{\text{dil. HCl}} \text{precipitate dissolves}
  2. Metallic sulphideA Pb(CH3COO)2 soln.black precipitate \text{Metallic sulphide} \quad \raisebox{0.35em}{A} \space \xrightarrow{\text{Pb(CH}_3{\text{COO}})_2 \text{ soln.}} \text{black precipitate }
  3. Metallic saltA BaCl2 soln.Barium sulphiteB dil. HClBarium chloride\text{Metallic salt} \quad \raisebox{0.35em}{A} \space \xrightarrow{\text{BaCl}_2 \text{ soln.}} \text{Barium sulphite} \quad \raisebox{0.35em}{B} \space \xrightarrow{\text{dil. HCl}} \text{Barium chloride}
  4. Metallic chlorideA conc. H2SO4ΔGas evolvedB AgNO3White precipitate\text{Metallic chloride} \quad \raisebox{0.35em}{A} \space \xrightarrow{\text{conc. H}_2\text{SO}_4\Delta} \text{Gas evolved} \quad \raisebox{0.35em}{B} \space \xrightarrow{\text{AgNO}_3} \text{White precipitate}
  5. Metallic saltA BaCl2White precipitate insoluble in dil. HCl\text{Metallic salt} \quad \raisebox{0.35em}{A} \space \xrightarrow{\text{BaCl}_2} \text{White precipitate insoluble in dil. HCl}

Answer

  1. Na2CO3 + Ba(NO3)2 ⟶ BaCO3 ↓ [white ppt.] + 2NaNO3
    BaCO3 + 2HCl ⟶ BaCl2 [soluble] + H2O + CO2

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

  3. Na2SO3 + BaCl2 ⟶ BaSO3 ↓ [white ppt.] + 2NaCl
    BaSO3 + 2HCl ⟶ BaCl2 [soluble] + H2O + SO2

  4. NaCl + H2SO4 [conc.] <200°C\xrightarrow{\lt 200 \degree\text{C}} NaHSO4 + HCl
    HCl + AgNO3 ⟶ AgCl ↓ [white ppt.] + HNO3

  5. Na2SO4 + BaCl2 ⟶ BaSO4 ↓ [white ppt.] + 2NaCl

Question 4

Complete the table given below :

Heat onGas evolvedColour of gasOdour of gasNature of gasSolubility of gas in waterColour of residue if any
1. KNO3            
2. (NH4)2Cr2O7            
3. ZnCO3            
4. Zn + dil. H2SO4            
5. Na2S + dil. H2SO4            
6. Na2SO3 + dil. H2SO4            
7. NaCl + conc. H2SO4            
8. NaNO3 + Cu + conc. H2SO4            
9. MnO2 + conc. HCl            
10. NH4Cl + NaOH            

Answer

Heat onGas evolvedColour of gasOdour of gasNature of gasSolubility of gas in waterColour of residue if any
1. KNO3O2ColourlessOdourlessNeutralSolubleWhite
2. (NH4)2Cr2O7N2ColourlessOdourlessNeutralSolubleGreenish
3. ZnCO3CO2ColourlessOdourlessAcidicSolubleYellow - hot
White - cold
4. Zn + dil. H2SO4H2ColourlessOdourlessNeutralsoluble-
5. Na2S + dil. H2SO4H2SColourlessRotten egg smellAcidicSoluble-
6. Na2SO3 + dil. H2SO4SO2ColourlessSuffocatingAcidicSoluble-
7. NaCl + conc. H2SO4HClColourlessPungentAcidicSoluble-
8. NaNO3 + Cu + conc. H2SO4NO2Reddish brownIrritatingAcidicsoluble-
9. MnO2 + conc. HClCl2Greenish yellowPungentAcidicSoluble-
10. NH4Cl + NaOHNH3ColourlessPungentBasicSoluble-

Question 5

Select the correct word from the words in bracket.

  1. The solution which on heating with CaCO3 evolves CO2 gas. [conc. H2SO4 / dil.H2SO4 / dil. HCl]
  2. The solution which can be used to distinguish an ammonium salt from a sodium salt. [CuCl2 soln. / NH4OH / dil. H2SO4 / AgNO3 soln.]
  3. The pH of blood is around 7.4, of saliva is 6.5 and of acid rain is around 4.5. The solution which is slightly alkaline of the three. [saliva / acid rain / blood]
  4. Decomposition of [NaCl / NaHCO3 / NaNO3] by dil. H2SO4, forms an unstable acid.
  5. A metal which reacts with an alkali to liberate hydrogen. [iron / copper / aluminium]

Answer

  1. dil. H2SO4
  2. CuCl2 soln
  3. blood
  4. NaHCO3
  5. aluminium.
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