Study of Acids, Bases and Salts ICSE Class 10 Chemistry

Students of ICSE Class 10 should refer to Study of Acids, Bases and Salts ICSE Class 10 Chemistry board year questions and solutions. below which have come in past board exams. You should always go through questions that have come in previous years. This will help you to understand the pattern of questions in ICSE Class 10 Chemistry and prepare accordingly. This will help you to get better marks in ICSE Class 10 Board Exams

ICSE Class 10 Chemistry Study of Acids, Bases and Salts Board Exam Questions

Students should learn the important questions and answers given below for Chapter Study of Acids, Bases and Salts in Chemistry for ICSE Class 10. These board questions are expected to come in the upcoming exams. Students of ICSE Class 10th should go through the below board exams questions and answers which will help them to get more marks in exams.

Board Exam Questions Study of Acids, Bases and Salts ICSE Class 10 Chemistry

Question: Salts of strong acids and strong bases in water produce (1) ……………solution. Solution of sodium carbonate in water is (2) ………………..in nature, while the solution of ferric chloride is (3) ………………in nature.

Answer

(1) Neutral, (2) basic, (3) acidic.

Question: A solution X turns blue litmus red, so it must contain :
(1) ………ions. Another solution Y turns red litmus blue and therefore, must contain
(2) ………ions. When solutions X and Y are mixed together, the products will be a (3)…… and
(4) ………. If a piece of magnesium was put into solution X. (5) ……… gas would be evolved.

Answer:

(1) hydronium, (2) hydroxide, (3) salt, (4) water, (5) hydrogen.

Question: In making copper sulphate crystals, a black powder called (1) ………… is added to dilute (2) ……… acid and the mixture is warmed. Excess black powder is added to a small volume of acid so as to (3) ……….. The excess insoluble black powder is got rid by (4) ……… The resulting clear solution looks (5) ……….. in colour. This solution is heated to get rid of some of the (6)……….. Slow cooling of the remaining solution (7) …………. of pure copper sulphate.

Answer

(1) Copper oxide, (2) Sulphuric, (3) neutralise the excess of the acid, (4) filtration, (5) blue, (6)
copper sulphide as impurity, (7) gives well-defined crystals.

Question: Deliquescence takes place because of the difference in (1) …………………………of atmospheric (2) ……………..and that of the deliquescent substance. The vapour pressure of atmospheric humidity is (3) ………than that of the deliquescent substance. The substances which take up water on exposure to atmosphere, without forming a solution are known as (4) …………….. substances.

Answer

Ans. (1) vapour pressure, (2) humidity, (3) higher, (4) hygroscopic.

(e) Question.. An acid is a compound which when dissolved in water gives ………………….. ions as the only ……………….. ions.

Answer

hydronium, positive

Question. A ………………….. acid undergoes almost complete dissociation on dissolving in water.

Answer

strong

Question. An example of mineral acid is ……………………

Answer

HCl

Question. Vinegar contains ………………….. acid.

Answer

acetic

Question. Sodium acetate on hydrolysis forms sodium hydroxide and ………………….. .

Answer

acetic acid

Question. The basicity of Acetic Acid is ………….

Answer

Question. Metal A reacts with cold water forming hydrogen and new compound B. The anion combined with A in a substance B is named ………………. .

Answer

hydroxyl ion

Question. The solution of sodium carbonate is alkaline due to ……………………….. .

Answer

hydrolysis

Question. The complete reaction between an acid and a base is called ………………… .

Answer

neutralization

Question. The pH value of a neutral solution is …………………………… .

Answer

Question. As the pH of solution decreases, its acidic strength progressively ………….. .

Answer

increases

Question. As the pH of solution increases, the ………………….. strength of the solution progressively decreases.

Answer

acidic

Question. pH value of lemon juice is ……………… than 7.

Answer

less

Question. Ammonium hydroxide is a ……………. base.

Answer

weak

Question. Methyl orange turns …………………… in acidic solution.

Answer

pink

Question. The formation of a salt from an acid and a base involves the combination of………………. from the acid and the……………….from the………………..to form………………….. molecules.

Answer

H+, OH–, base, water

Question. A salt which absorbs moisture from the air, but does not change in physical state in called ……………….. salt.

Answer

hygroscopic

Question. Ammonium chloride is a ………………….. salt.

Answer

soluble

Question. Sodium hydrogen sulphate is ……………. salt.

Answer

acidic

Question. The salt of the acid HNO2 are called…………………..and those of the acid HNO3 are called ………………… .

Answer

nitrites, nitrates

Question. Sodium sulphite reacts with dilute sulphuric acid to form sodium sulphate …………….. gas and water.

Answer

Sulphur dioxide

Question. Copper (II) chloride reacts with sodium hydroxide to form …………………. copper hydroxide and sodium chloride.

Answer

insoluble

Question. A chemical reaction between hydronium ions of an acid and OH– ions of a base to form unionised water is called ……………………… .

Answer

neutralization

Question. Dissolving of aluminium foil in HCl as well as NaOH shows that it is ……………. in nature.

Answer

amphoteric

Question. An example of a deliquescent salt is ……………………..

Answer

anhydrous (CaCl₂)

Question. Superphosphate is an example of a compound called………… .

Answer

acid salt

Question. The number of H+ ions of an acid which react completely with one molecule of a base is called its …………. .

Answer

acidity

Question. When a metallic oxide is dissolved in water, the solution formed has high concentration of……………ions.

Answer

OH–

Question. The metal which does not react with water or dilute H2SO4 but reacts with concentrated H2SO4 is…………….

Answer

Question. The metal whose oxide, which is amphoteric, is reduced to metal by carbon reduction………….

Answer

Question. The divalent metal whose oxide is reduced to metal by electrolysis of its fused saltis………….

Answer

Question. Higher the pH value of a solution, the more…………it is.

Answer

alkaline

Multiple Choice Questions

Question. A particular solution contains molecules and ions of the solute so it is a :
(a) Weak acid
(b) Strong acid
(c) Strong base
(d) Salt solution

Answer

Question. Select the acid which contains four hydrogen atoms in it :
(a) Formic acid
(b) Sulphuric acid
(c) Nitric acid
(d) Acetic acid

Answer

Question. An organic weak acid is :
(a) Formic acid
(b) Sulphuric acid
(c) Nitric acid
(d) Hydrochloric acid

Answer

Question. The aqueous solution of the following compounds which contains both ions and molecules is :
(a) Sulphuric acid
(b) Hydrochloric acid
(c) Nitric acid
(d) Acetic acid

Answer

Question. An acid which is not a hydro acid is :
(a) H₂S
(b) H₂SO₃
(c) HBr
(d) HCl

Answer

Question. Which one of the following will not produce an acid when made to react with water ?
(a) Carbon monoxide
(b) Carbon dioxide
(c) Nitrogen dioxide
(d) Sulphur trioxide

Answer

Question. The metal oxide which can react with acid as well as alkali is :
(a) Silver oxide
(b) Copper (II) oxide
(c) Aluminium oxide
(d) Calcium oxide

Answer

Question. During ionization metals lose electrons, this change can be called :
(a) Oxidation
(b) Reduction
(c) Redox
(d) Displacement

Answer

Question. The salt which in solution gives a pale green precipitate with sodium hydroxide solution and a white precipitate with barium chloride solution is :
(a) Iron (III) sulphate
(b) Iron (II) sulphate
(c) Iron (II) chloride
(d) Iron (III) chloride

Answer

Question. An example of a complex salt is :
(a) Zinc sulphate
(b) Sodium hydrogensulphate
(c) Iron (II) ammonium sulphate
(d) Tetrammine copper (II) sulphate

Answer

Question. To increase the pH value of neutral solution, we should add :
(a) An acid
(b) An acid salt
(c) An alkali
(d) A salt

Answer

Give One Word/Chemical Term

Question. Name the acids, which are used in food stuffs.

Answer

Citric acid, tartaric acid and acetic acid

Question. Two monobasic acids containing nitrogen.

Answer

Nitric acid and nitrous acid

Question. Two dibasic acids containing sulphur.

Answer

Sulphuric acid and sulphurous acid

Question. Strong acid containing chlorine.

Answer

Hydrochloric acid

Question. Two gases–one of which is basic and which combine to give a solid

Answer

Ammonia and hydrogen chloride

Question. Basic anhydride of calcium hydroxide.

Answer

Calcium oxide

Question. Product obtained when lime water dries up.

Answer

Calcium oxide and carbon dioxide

Question. Three common indicators to indicate presence of acids and alkalies.

Answer

Litmus, methyl orange, phenolphthalein

Question. This gas turns moist lead acetate paper black.

Answer

Hydrogen sulphide

Question. The compound which is responsible for the green colouration when sulphur dioxide is passed through acidified potassium dichromate solution.

Answer

Chromium sulphate

Question. The compound responsible for the brown ring during the brown ring test of nitrate ion.

Answer

Nitroso Iron (II) sulphate

Question. A salt formed by incomplete neutralisation of an acid by a base.

Answer

Acid salt

Question. This salt gives nitrogen dioxide on heating.

Answer

Pb(NO3)2

Question. This compound is an acid salt.

Answer

Methane

Question. On heating, this salt changes from green to black.

Answer

CuCO3

Question. On treating with concentrated sulphuric acid, this salt changes from blue to white.

Answer

CuSO4.5H2O

Question. A compound which is insoluble in cold water, but soluble in hot water.

Answer

Lead (II) chloride

Question. A compound whose aqueous solution is neutral in nature.

Answer

Sodium chloride

Question. Three metals that can form bases when treated with water.

Answer

Sodium, calcium and potassium

Question. Acid anhydride of sulphuric acid.

Answer

Sulphur trioxide

Question. The process in which a substance absorbs moisture from the atmospheric air to become moist, and ultimately dissolves in the absorbed water.

Answer

Deliquescence

Question. A compound which is deliquescent.

Answer

Caustic Soda (NaOH)

Question. Name an acidic hygroscopic substance.

Answer

Sulphuric acid, or oil of vitriol

Question. Name a basic hygroscopic substance.

Answer

Calcium oxide

Question. Name any two efflorescent substances.

Answer

Copper sulphate (Blue vitriol) and Washing soda (Sodium carbonate)

Define/Explain the Following

1. An acid
A compound which on dissolving in water furnishes a proton [Hydrogen ion (H+)] as the only positively charged ion is called acid or it is a compound which dissolves in water to
form hydronium ion, i.e., HCl, H₂SO₄ etc.

2. A base
A base is a compound which combines with the hydronium ion (H₃O⁺) of an acid to form salt and water only, or it is the oxide or hydroxide of a metal which will neutralize the acid.

3. An alkali
An alkali is a compound, which on dissolving in water furnishes OH– ions as only negative ions, e.g., NaOH, KOH etc. The soluble bases are called alkali.

4. Salts
A salt is an ionic compound which when dissolved in water, yields a positive ion other than hydrogen ion (H⁺) and a negative ion other than hydroxyl ion (OH^–).

5. Normal salt
A normal salt is one which does not contain any of ionisable or replaceable hydrogen atoms in its molecule. For example : NaCl, Na₂SO₄, AgCl, FeCl₃ etc.

6. Acid salt
An acid salt contains one or more partially replaceable hydrogen ions (H+) in it. For example : NaHCO₃, KHSO₃, Ca(HCO₃)₂ etc.

7. Basic salt
A basic salt is formed as a result of incomplete neutralisation of a base by an acid. It contains replaceable hydroxyl ions (OH^–). For example : CuCO₃, Cu(OH)₂, PbCO₃, Pb(OH)₂ etc.

Balancing/Writing the Chemical Equations

(a) Write correctly balanced equations for the following reactions :

1. Molten sodium and chlorine.

Answer

1. 2Na + Cl₂ ⎯⎯→ 2NaCl

2. Nitrogen and oxygen, when lightning strikes.

Answer

2. N₂ + O₂ ⎯⎯→ 2NO

3. Iron and dilute sulphuric acid.

Answer

3. Fe + H₂SO₄ ⎯⎯→ FeSO₄ + H₂

4. Decomposition of hypochlorous acid in sunlight.

Answer

5. Decomposition of potassium nitrate.

Answer

5. 2KNO₃ ⎯⎯→ 2KNO₂ + O₂

6. Sodium thiosulphate is reacted with dilute hydrochloric acid.

Answer

6. Na₂S₂O₃ + 2HCl ⎯→ 2NaCl + SO₂ + + S ↓ + H₂O

7. Calcium bicarbonate reacts with dilute hydrochloric acid.

Answer

7. Ca(HCO₃)₂ + 2HCl ⎯→ CaCl₂ + 2H₂O + 2CO₂ ↑

8. Dilute sulphuric acid is poured over sodium sulphate.

Answer

8. Na₂SO₃ + H₂SO₄ (dilute) ⎯→ Na₂SO₄ + H₂O + SO₂ ↑

9. Lead nitrate solution is added to sodium chloride solution.

Answer

9. Pb(NO₃)₂ + 2NaCl ⎯→ PbCl₂ + 2NaNO₃

10. Zinc is heated with sodium hydroxide solution.

Answer

10. Zn + 2NaOH ⎯→ Na₂ZnO₂ + H₂ ↑

11. Lead sulphate from lead nitrate solution and dilute sulphuric acid.

Answer

11. Pb(NO₃)₂ + H₂SO₄ ⎯→ PbSO₄ ↓ + 2HNO₃
Lead Sulphuric Lead Nitric acid
nitrate acid sulphate

12. Copper sulphate from copper and concentrated sulphuric acid.

Answer

Cu + 2H₂SO₄ ⎯→ CuSO₄ + 2H₂O + SO₂
Copper Sulphuric Copper Water Sulphur
acid sulphate dioxide

13. Lead chloride from lead nitrate solution and sodium chloride solution.

Answer

Pb(NO₃)₂ + 2NaCl ⎯→ PbCl₂ + 2NaNO₃
Lead Sodium Lead Sodium
nitrate chloride chloride nitrate

14. Ammonium sulphate from ammonia and dilute sulphuric acid.

Answer

14. 2NH₃ + H₂SO₄ ⎯→ (NH₄)₂SO₄
Ammonia Sulphuric Ammonium
acid sulphate

15. Sodium chloride from sodium carbonate solution and dilute hydrochloric acid.

Answer

15. Na₂CO₃ + 2HCl ⎯→ NaCl + H₂O + CO₂
Sodium Hydrochloric Sodium Water Carbon
carbonate acid chloride dioxide

16. Magnesium and dilute sulphuric acid.

Answer

16. MgO + H₂SO₄ (dil.) ⎯→ MgSO₄ + H₂↑

17. Zinc carbonate and dilute sulphuric acid.

Answer

17. ZnCO₃ + H₂SO₄ ⎯→ ZnSO₄ + H₂O + CO₂ ↑

18. Copper oxide and dilute sulphuric acid.

Answer

18. CuO + H₂SO₄ (dil.) ⎯→ CuSO₄ + H₂O

19. Ferric hydroxide reacts with nitric acid.

Answer

19. Fe(OH)₃ + 3HNO3 ⎯→ Fe(NO₃)₃ + 3H₂O

20. Zinc oxide dissolves in sodium hydroxide.

Answer

20. ZnO + 2NaOH ⎯→ Na₂ZnO₂ + H₂O

(b) Write the equation for the laboratory preparation of the following salts.
1. Iron(II) sulphate from iron.

Answer

2. Copper sulphate from copper.

Answer

3. Lead sulphate from lead nitrate.

Answer

4. Sodium sulphate from sodium carbonate.

Answer

Na2CO₃ + H₂SO₄ ⎯→ Na₂SO₄ + H₂O + CO₂

5. Copper sulphate from copper(II) oxide.

Answer

CuO + H₂SO₄ ⎯→ CuSO₄ + H₂O
Copper(II) oxide Copper
sulphate

6. Iron(III) chloride from iron.

Answer

2Fe + 3Cl₂ ⎯→ 2FeCl₃
Iron Chlorine Ferric chloride

7. Potassium sulphate from potassium hydroxide solution.

Answer

8. Lead chloride from lead carbonate (two equations).

Answer

9. Zinc sulphate from zinc.

Answer

9. Zn + H₂SO₄ ⎯→ ZnSO₄ + H₂ ↑
(dil.)

10. Sodium sulphate from sodium hydroxide.

Answer

10. 2NaOH + H₂SO₄ ⎯→ Na₂SO₄ + 2H₂O
(dil.)

11. Lead(II) chloride from lead nitrate.

Answer

Pb (NO₃)₂ + 2HCl ⎯→ PbCl₂ + 2HNO₃

12. Copper(II) sulphate from copper carbonate.

Answer

CuCO₃ + H₂SO₄ ⎯→ CuSO₄ + H₂O + CO₂
Copper (dil.) Copper(II)
carbonate sulphate

13. Calcium carbonate from calcium chloride.

Answer

CaCl₂ + Na₂CO₃ ⎯→ CaCO₃ + 2NaCl

14. Sodium sulphate from sodium carbonate.

Answer

Na₂CO₃ + H₂SO4 ⎯→ Na₂SO₄ + H₂O + CO₂
Sodium dil. Sodium
carbonate sulphuric acid sulphate

15. Zinc carbonate from zinc nitrate.

Answer

Zn(NO₃)₂ + Na2CO₃ ⎯→ ZnCO₃+ 2NaNO₃
Zinc nitrate Sodium Zinc Sodium
carbonate carbonate nitrate

(c) Study the following conversion schemes :
1. Give the equations for the following conversions A to E.

2. Refer to the flow chart diagram below and give balanced equations with conditions, if any, for the following conversions A to D.

(i) For each of the conversions A to D in the above state briefly how the conversions can be carried out.
(ii) Write equations for the conversions.

4. For each of the conversion in the scheme given below, state briefly in words or by means of chemical equation, how the conversion is carried out ?

5. How are the following conversions carried out ? Give balanced chemical equations only.

Ans.

3.
[A] Lead(II) oxide, when heated with powdered coke, reduced to metallic lead and carbon monoxide is formed.
PbO + C ⎯→ Pb + CO

[B] Lead(II) oxide, when dissolved in the dilute nitric acid, lead nitrate is formed.
PbO + 2HNO₃ ⎯→ Pb(NO₃)₂ + H₂O
Lead nitrate

[C] Lead(II) nitrate is dissolved in water and then sodium hydroxide solution is added, a white precipitate of lead hydroxide is obtained.
Pb(NO₃)₂ + 2NaOH ⎯→ Pb(OH)₂ + 2NaNO₃

[D] Lead(II) nitrate is dissolved in water and then concentrated solution of sodium carbonate is added, a white precipitate of lead (II) carbonate is obtained.
Pb(NO₃)₂ + Na₂CO₃ ⎯→ PbCO₃ + 2NaNO₃

[A] Copper(II) oxide, when heated with coke powder is reduced to metallic copper.
CuO + C ⎯→ Cu + CO
Metallic copper

[B] Copper(II) oxide is dissolved in dilute sulphuric acid to form copper sulphate.
CuO + H₂SO₄ ⎯→ CuSO₄ + H₂O
Copper
sulphate

[C] Copper sulphate is dissolved in water and hydrogen sulphide gas is passed, a black precipitate of copper sulphide is formed.
CuSO₄ + H₂S ⎯→ CuS + H₂SO₄
Black ppt.

[D] Copper(II) oxide is dissolved in dilute hydrochloric acid to form copper chloride. To the solution of copper chloride, when a saturated solution of sodium carbonate is added, a light blue precipitate of copper(II) carbonate is formed.
CuCl₂ + Na₂CO₃ ⎯→ CuCO₃ + 2NaCl

(d) How can the following be converted to the respective chloride, sulphate and nitrate salts ? Give equations :

1. Magnesium, 2. Zinc, 3. Iron, 4. Lead carbonate, 5. Copper oxide, 6. Potassium hydroxide, 7. Copper hydroxide, 8. Ammonium hydroxide.

Ans.

Ans. (i) CaCO₃ + 2HCl ⎯→ CaCl₂ + H₂O + CO₂
(ii) NaHCO3 + HNO₃ ⎯→ NaNO₃ + H₂O + CO₂
(iii) ZnSO₃ + 2HCl ⎯→ ZnCl₂ + H₂O + SO₂
(iv) 2KHSO₃ + H₂SO₄ ⎯→ K₂SO₄ + 2H₂O + 2SO₂

Chemical Tests

Q. How will you distinguish between the following pairs of compounds :
1. Iron(II) chloride and Iron(III) chloride.

Answer

Iron(II) chloride is dissolved in water and then sodium hydroxide is added. A dirty green precipitate is obtained which confirms the presence of iron(II) chloride.
FeCl₂ + 2NaOH ⎯→ Fe(OH)₂ + 2NaCl
Iron(III) chloride is also dissolved in water and then sodium hydroxide solution is added. A reddish brown precipitate is obtained, which confirms the presence of iron(III) chloride.
FeCl₃ + 3NaOH ⎯→ Fe(OH)₃+ 3NaCl

2. Lead nitrate and copper nitrate.

Answer

Lead nitrate is dissolved in water and then sodium hydroxide solution is added, a white precipitate is obtained, which is soluble in excess of sodium hydroxide.
Pb(NO₃)₂+ 2NaOH ⎯→ Pb(OH)₂ + 2NaNO₃
Copper nitrate is dissolved in water and sodium hydroxide solution is added, a light blue precipitate of copper hydroxide is obtained.
Cu(NO₃)₂ + 2NaOH ⎯→ Cu(OH)₂ + 2NaNO₃

3. Zinc oxide and calcium oxide.

Answer

Zinc oxide is dissolved in dilute hydrochloric acid to form zinc chloride and then sodium hydroxide solution is added, a white precipitate is obtained, which is soluble in excess of
sodium hydroxide to form a clear solution.
ZnO + 2HCl ⎯→ ZnCl2 + H2O
ZnCl2 + 2NaOH ⎯→ Zn(OH)2 + 2NaCl
Zn(OH)2 + 2NaOH ⎯→ Na2ZnO2 + 2H2O
Sodium zincate
(A clear solution)

Calcium chloride is obtained by dissolving calcium oxide in dilute hydrochloric acid. To the solution of calcium chloride, sodium hydroxide solution is added, a white precipitate of
calcium hydroxide is obtained, which is insoluble even in the excess of sodium hydroxide.
  CaO + 2HCl ⎯→ CaCl2 + H2O
  CaCl2 + 2NaOH ⎯→ Ca(OH)2 + 2NaCl
  Calcium hydroxide

4. Sodium carbonate and sodium nitrate.

Answer

Sodium carbonate when treated with dilute hydrochloric acid, a vigorous reaction takes place and a colourless, odourless gas carbon dioxide is evolved which turns lime water milky.
Na₂CO₃+ 2HCl ⎯→ 2NaCl + H₂O + CO₂
Sodium nitrate when mixed with copper filings and heated with concentrated sulphuric acid, reddish brown fumes of nitrogen dioxide are evolved.
2NaNO₃ + H₂SO₄⎯→ Na2SO4 + 2HNO₃
Cu + 4HNO₃ ⎯→ Cu(NO₃)₂+ 2NO₂+ 2H₂O

5. Sodium sulphate and sodium sulphite.

Answer

Sodium sulphate is dissolved in water and barium chloride solution is added, an insoluble white precipitate of barium sulphate is obtained.
Na₂SO₄ + BaCl₂ ⎯→ BaSO₄ + 2NaCl
White ppt.
Sodium sulphite is warmed with dilute sulphuric acid, a colourless gas with a pungent and suffocating smell is evolved. When this gas is bubbled through acidified solution of potassium dichromate, it turns its colour from orange to green.
Na₂SO₃ + H₂SO₄ ⎯→ Na₂SO₄ + H₂O + SO₂
K₂Cr₂O₇ + H₂SO₄ + 3SO₂ ⎯→ K₂SO₄ + Cr₂(SO₄)₃ + H₂O

6. How will you distinguish between ammonium hydroxide and sodium hydroxide using copper sulphate solution ?

Answer

When ammonium hydroxide solution is added drop by drop to copper sulphate solution, a pale blue or bluish white precipitate is formed which is soluble in excess of ammonium
hydroxide and a deep blue or inky blue solution is formed with excess of ammonium hydroxide.
CuSO₄ + 2NH₄OH ⎯→ Cu(OH)₂ + (NH₄)2SO₄
Cu(OH)₂ + 4NH₄OH ⎯→ [Cu(NH₃)₄](OH)₂ + 4H₂O
Copper solution forms a blue precipitate with sodium hydroxide solution. It is insoluble in excess of NaOH.
CuSO₄ + 2NaOH ⎯→ Cu(OH)₂ + Na₂SO₄
Copper Sodium Copper Sodium
sulphate hydroxide hydroxide sulphate

Reasoning Based Questions

Q. 1. Hydrochloric acid is considered as a strong acid whereas acetic acid is a weak acid. Why ?

Answer

Hydrochloric acid is considered as a strong acid because it dissociates completely in water.
HCl (aq.) ⇌ H⁺ (aq.) + Cl^– (aq.)
Acetic acid is a weak acid as it dissociates partially when dissolved in water. Most of its molecules remain in molecular form in the solution.
CH₃COOH (aq) ⇌ CH₃COO^– (aq) + H⁺ (aq)

Q. 2. Why dilute sulphuric acid is stronger acid than concentrated sulphuric acid ?

Answer

The presence of water in dilute sulphuric acid increases the hydrogen ion concentration. Hence it is a stronger acid than concentrated sulphuric acid which contains comparatively less water.

Q. 3. Acetic acid is monobasic. Why ?

Answer

Acetic acid is monobasic because it has one ionisable hydrogen ion and combines with one hydroxyl ion of the base to give a single salt and water.
CH₃COOH ⇌ CH₃COO^–+ H⁺
NaOH + CH₃COOH ⎯⎯→ CH₃COONa + H₂O

Q. 4. Carbonic acid is a dibasic acid. Why ?

Answer

Carbonic acid (H₂CO₃) is a dibasic acid because it has two replaceable hydrogen atoms and hence it combines with two hydroxyl groups of the bases to form two kinds of salt and water.
H₂CO₃ ⇌ HCO₃^– + H⁺
HCO₃ ⇌ CO₃^2– + H⁺
The displacement of two hydrogen atoms takes place in two steps.

Q. 5. Sodium hydroxide is a monoacidic base. Why ?

Answer

Sodium hydroxide is a mono-acidic base as it combines with only one hydrogen ion.
NaOH (aq) + HCl (aq) ⎯→ NaCl (aq) + H₂O (l)

Q. 6. An aqueous solution of the salt ammonium chloride is acidic in nature while an aqueous solution of sodium chloride is neutral. Why ?

Answer

Ammonium chloride is a salt of weak base and strong acid, it undergoes salt hydrolysis to produce an acidic solution whereas sodium chloride is a salt of strong acid and strong base, it does not undergo salt hydrolysis hence its solution remains neutral.

Q. 7. An aqueous solution of the zinc sulphate is acidic in nature. Why ?

Answer

When zinc sulphate is dissolved in water, it is hydrolysed to form sulphuric acid and zinc hydroxide. Sulphuric acid is a strong acid, while zinc hydroxide is a weak base, hence, the solution is acidic in nature.
ZnSO₄ + 2H₂O ⎯→ Zn(OH)₂ + H₂SO₄
Weak base Strong acid

Q. 8. An aqueous solution of ammonium acetate is neutral in nature. Why ?

Answer

Ammonium acetate, when dissolved in water is hydrolysed to form ammonium hydroxide and acetic acid. Ammonium hydroxide and acetic acid both are weak alkali and acid respectively, hence the solution is neutral in nature.

Q. 9. An aqueous solution of sodium carbonate is alkaline and that of ammonium chloride is acidic in behaviour. Why ?

Answer

An aqueous solution of sodium carbonate is alkaline and that of ammonium chloride is acidic in behaviour. Why ?
Ans. Both of these salts react with water. Sodium carbonate reacts with water, producing a strong alkali, sodium hydroxide and a weak acid, carbonic acid. Hence, the solution is alkaline :
Na₂CO₃ + H_2 ^⇌ 2NaOH + H₂CO₃
Ammonium chloride reacts with water to produce ammonium hydroxide, a weak alkali and hydrochloric acid, a strong acid. Hence the solution is acidic :
NH₄Cl + H₂ ⇌ NH₄OH + HCl

Q. 10. A universal indicator is more meaningful than an ordinary indicator.

Answer

A universal indicator is better than an ordinary indicator as it not only shows whether the solution is acidic or basic but also gives the pH values (approx.) by giving a wide range of colours corresponding to different pH values.

Short Questions

Q. 1. Solution A is a strong acid, solution B is a weak acid, solution C is a strong alkali.
(i) Which solution contains solute molecules in addition to water molecules.
(ii) Which solution could be a solution of glacial acetic acid ?
(iii) Give an example of a solution which is a weak alkali.

Answer

(i) B (ii) B (iii) Ammonium hydroxide

Q. 2. (i) What is basicity of an acid. Give examples.
(ii) Give the basicity of nitric acid, acetic acid and phosphoric acid.
(iii) State two properties of an acid.
(iv) On what factors the strength of an acid depend ?
(v) Name an acid used : (a) as a flavour and to preserve food, (b) in a drink, (c) to remove ink spots, (d) as an eye wash.

Answer

(i) The number of replaceable hydrogen atoms, present in one molecule of an acid is known as basicity of the acid. For example hydrochloric acid is a monobasic acid, sulphuric acid is a dibasic acid and phosphoric acid is a tribasic acid.
(ii) Nitric acid (HNO₃) ⎯→ Monobasic
Acetic acid (CH₃COOH) ⎯→ Monobasic
Phosphoric acid (H₃PO₄) ⎯→ Tribasic.
(iii) (a) An acid turns methyl orange into pink and blue litmus to red.
(b) An acid with a base forms salt and water only.
NaOH + HCl ⎯→ NaCl + H₂O
(Alkali) (Acid) (Salt) (Water)
(iv) The strength of an acid depends on the following factors :
(a) Reactivity of the acid.
(b) Degree of ionisation to H+ ion.
(v) (a) Citric acid. (b) Carbonic acid.
(c) Oxalic acid. (d) Boric acid.

Q. 3. (i) What is acidity of a base. Give examples.
(ii) State three properties of an alkali.

Answer

(i) The number of hydroxyl ions that one molecule of a base gives on dissociation is known as acidity of a base. e.g., The acidity of sodium hydroxide (NaOH) is one, it is a monoacid, the acidity of Ca(OH)₂ is two, it is a diacid base, Al(OH)₃ is a triacid base.
(ii) An alkali turns :
(a) Red litmus blue (b) Phenolphthalein to pink (c) Methyl orange to yellow.

Q. 4. Name the kind of particles present in :
(i) Sodium hydroxide solution. (ii) Carbonic acid (iii) Sugar solution.

Answer

(i) Sodium ions and hydroxide ions.
(ii) Carbonic acid molecules, carbonate ions and hydronium ions.
(iii) Sugar molecules and water molecules.

Q. 5. Solution A is a sodium hydroxide solution. Solution B is a weak acid. Solution C is dilute sulphuric acid. Which solution will :
(i) Liberate sulphur dioxide from sodium sulphite.
(ii) Give a white precipitate with zinc sulphate solution.
(iii) Contain solute molecules and ions.

Answer

(i) C (ii) A (iii) B

Q. 6. (i) What are indicators ?
(ii) Name three indicators and their colours in different medium.
(iii) What is reaction of neutralization ?
(iv) Give two practical application of neutralization.

Answer

(i) Indicators are complex organic compounds, which are used to distinguish between acidic and alkaline solutions by the abrupt change in their colour, e.g. litmus, methyl orange and phenolpthalein.

Q. 7. (i) Explain pH value of a solution.
(ii) What is the pH of :
(a) Pure water (b) Milk (c) Human blood
(iii) The pH value of three solutions is given below. Which one of them is acidic, neutral and alkaline in nature ?
(a) pH = 7 (b) pH = 10 (c) pH = 3
(iv) What is pH number assigned to a solution ?

Answer

(i) pH value of a solution is the negative logarithm to the base 10 of hydrogen ion concentration expressed in gram-ions per litre.
pH = log10 [H+]
pH value = 7 indicates a neutral solution.
pH value > 7 indicates an alkaline solution.
pH value < 7 indicates an acidic solution.
(ii) The pH of :
(a) Pure water is 7 (b) Milk is 6·6 (c) Human blood is 7·3
(iii) (a) Neutral (b) Alkaline (c) Acidic
(iv) It is a number assigned to express the acidity or alkalinity of a solution which varies from 1b to 14. The pH number less than 7 indicates acidity, while pH number more than 7 indicates alkalinity. The pH of pure water is 7 and it is neutral.

Q. 8. (i) (a) What is the purpose of the pH scale ?
(b) What is the pH of pure water.
(c) A is a soluble acidic oxide, B is a soluble base compared to the pH of pure water, what will be the pH of : (i) a solution of A, (ii) a solution of B.
(ii) Taking sodium carbonate as an example, give the meaning of the following terms :
(a) Water of crystallization (b) Anhydrous (c) Efflorescence.

Answer

(i) (a) To measure the degree of acidity or alkalinity.
(b) The pH of pure water is equal to 7.
(c) (i) The pH is less than 7. (ii) The pH is more than 7.
(ii) (a) Water of crystallization is that definite number of water molecules which a crystal contain when it is crystallizing out from an aqueous solution. e.g., Sodium carbonate crystal contains 10 molecules of water i.e., Na₂CO₃. 10H₂O.
(b) When Na₂CO₃.10H₂O is heated, the water of crystallization is evaporated leaving anhydrous sodium carbonate Na₂CO₃.
(c) The loss of water by a hydrate salt on exposure to air is called efflorescence, e.g.
Na₂CO₃.10H₂O on exposure to air, looses 9 molecules of water of crystallization.
Na₂CO₃. 10H₂O ^Air⎯⎯→Na₂CO₃. H₂O + 9H2O.

Q. 9. A solution has a pH of 7 explain how you would :
(i) (a) Increase its pH, (b) Decrease its pH.
(ii) If a solution changes the colour of litmus red to blue what can you say about its pH ?
(iii) What can you say about the pH of a solution that liberates carbon dioxide from sodium carbonate.

Answer

(i) (a) pH is increased by adding any caustic alkali to solution.
(b) pH is decreased by adding any mineral acid to solution.
(ii) pH of solution is more than 7.
(iii) pH of solution is less than 7.

Q. 10. (i) The pH value is utilised in medicine and agriculture. Explain.
(ii) The pH value of pure water is 7. Compare the pH values of sulphur dioxide solution and ammonia solution with that of pure water.
(iii) How does pH value of a solution and hydrogen ion concentration of solution vary ?

Answer

(i) (a) In medicine : The pH values of urine and blood are used to diagnose various diseases.
(b) In agriculture : The pH of soil is checked to ensure fast growth of crops. For example, citrus fruits need slightly alkaline soil, rice crop needs an acidic soil, sugarcane needs a neutral soil.
(ii) Sulphur dioxide is a non-metal oxide, such oxides are acidic with pH less then 7. Ammonia solution is alkaline with pH more than 7.
(iii) Both varies inversely. It is seen that lower the pH value the greater the H+ ion concentration and higher the pH value the lower the H+ ion concentration.