Chapter 4.4 – Acids Bases and Salts | Chapter Solution Class 9

Multiple Choice Questions (MCQ)

[Each of Mark-1]

Question 1

Which one is not an Arrhenius acid?

1. HCl
2. HF
3. HNO₃
4. C₂H₂

Answer

C₂H₂

Explanation

C₂H₂ is not an Arrhenius acid because it does not produce H⁺ ions in water. The other three acids ionize in water to produce H⁺ ions.

Question 2

An acid is a compound

1. having hydrogen atom
2. having lone pair of electron
3. that can donate proton
4. that can accept proton

Answer

that can donate a proton

Explanation

An acid is a compound that can donate a proton to another molecule or accept an electron pair, typically having a hydrogen atom.

Question 3

A base is that

1. has oxygen atom
2. can accept proton
3. can donate proton
4. is sour in taste

Answer

can accept proton

Explanation

A base is a compound that can accept a proton, typically having an oxygen atom, and has a bitter taste.

Question 4

Which is amphiprotic?

1. HCN
2. NH₃
3. NaOH
4. H₂O

Answer

H₂O

Explanation

Amphiprotic refers to a substance that can act as both an acid and a base, meaning it can donate or accept protons.

Question 5

Which one is not a strong acid?

1. HNO₃
2. HCl
3. H₂SO₄
4. CH₃COOH

Answer

CH₃COOH

Explanation

CH₃COOH is not a strong acid. HNO₃, HCl, and H₂SO₄ are strong acids that ionize completely in water.

Question 6

Baking soda consists of

1. Na₂CO₃
2. H₂CO₃
3. NaHCO₃
4. CH₃COOH

Answer

NaHCO₃

Explanation

Baking soda consists of NaHCO₃, which is sodium bicarbonate. When heated or reacted with acid, it releases CO₂ gas.

Question 7

Baking powder is a mixture of NaHCO₃ and

1. Vinegar
2. CH₃COOH
3. Oxalic acid
4. tartaric acid

Answer

tartaric acid

Explanation

Baking powder is a mixture of NaHCO₃ and tartaric acid or a similar acid, which releases CO₂ gas when heated.

Question 8

Which one is salt?

1. HCl
2. NH₃
3. NaCl
4. H₂O

Answer

NaCl

Explanation

NaCl (sodium chloride) is a salt, formed from the reaction between an acid and a base. HCl is an acid, NH₃ is a base, and H₂O is a neutral compound.

Question 9

 Which one is a normal salt ?

1. Na₂SO₄
2. NaHSO₄
3. NaHCO₃
4. Pb(OH)Cl

Answer

Na₂SO₄

Explanation

Na₂SO₄ (sodium sulfate) is a normal salt because it is derived from a strong base (NaOH) and a strong acid (H₂SO₄) and does not have acidic or basic properties. The other compounds are either acidic or basic salts. NaHSO₄ (sodium bisulfate) and NaHCO₃ (sodium bicarbonate) are acidic salts because they are derived from a weak base (NaHCO₃) and a strong acid (H₂SO₄) or a weak acid (H₂CO₃) and a strong base (NaOH), respectively. Pb(OH)Cl (lead(II) hydroxychloride) is a basic salt because it is derived from a strong base (NaOH) and a weak acid (HCl).

Question 10

Which one is an acid salt ?

1. NaHSO₄
2. NaCl
3. Na₂SO₄
4. Cu(OH)NO₃

Answer

NaHSO₄

Explanation

NaHSO₄ (sodium bisulfate) is an acid salt as it is formed from the partial neutralization of sulfuric acid (H₂SO₄) with sodium hydroxide (NaOH), resulting in an ion that has acidic properties. NaCl and Na₂SO₄ are normal salts while Cu(OH)NO₃ is a basic salt.

Question 11

Which one is a basic salt?

1. Na₂SO₄
2. Na₂HPO₄
3. NaCl
4. Pb(OH)Cl

Answer

Pb(OH)Cl

Explanation

Pb(OH)Cl (lead(II) hydroxychloride) is a basic salt as it is derived from a strong base (NaOH) and a weak acid (HCl), resulting in an ion that has basic properties. Na2SO4 and NaCl are normal salts while Na2HPO4 is an acidic salt.

Question 12

Which one is a double salt?

1. Ca(OCl)Cl (bleaching powder)
2. NaKCO₃
3. [Cu(NH₃)₄]SO₄
4. FeSO₄.(NH4)2SO4-6H2O (Mohr’s salt)

Answer

FeSO₄.(NH₄)2SO₄.6H₂O (Mohr’s salt)

Explanation

FeSO₄.(NH₄)2SO₄.6H₂O (Mohr’s salt) is a double salt that forms a blue-green crystalline compound. NaKCO₃ is a mixture of two different salts, while Ca(OCl)Cl (bleaching powder) and [Cu(NH₃)₄]SO₄ are not double salts.

Question 13

pH is defined as

1. [H₃O⁺]
2. log [H₃O⁺]
3. – log [H₃O⁺]
4. – [H₃O⁺]

Answer

-log[H₃O⁺]

Explanation

pH is defined as -log[H₃O⁺], where [H₃O⁺] is the concentration of hydronium ions in a solution. It is a measure of the acidity or basicity of a solution, with lower pH values indicating higher acidity and higher pH values indicating higher basicity.

Question 14

In neutral water at 25°C, [H⁺] in mol/L is

1. 10⁷
2. 10.7
3. 10^-7
4. 1.0

Answer

10^-7

Explanation

In neutral water at 25°C, [H+] (the concentration of hydronium ions) is 10^-7 mol/L. This means that the concentration of hydroxide ions is also 10^-7 mol/L, resulting in a neutral pH of 7.

Question 15

For an aqueous solution at 25°C, pH + pOH is

1. 10
2. 7
3. 12
4. 14

Answer

14

Explanation

For an aqueous solution at 25°C, pH + pOH = 14. This is because pH is defined as -log[H+] and pOH is defined as -log[OH^–], and the product of [H⁺] and [OH^–] in water is always 10^-14 at 25°C. Therefore, pH + pOH = -log[H⁺] + (-log[OH^–]) = -log([H⁺][OH^–]) = -log(10^-14) = 14.

Question 16

pH of pure boiling water is

1. 7
2. < 7
3. 12
4. 14

Answer

7

Explanation

The pH of pure boiling water is approximately 7 at standard pressure and temperature. However, it can be slightly acidic or basic due to dissolved gases or impurities.

Question 17

An acid-base indicator is an organic dye which is chemically

1. a weak acid
2. a weak base
3. either a weak acid or a weak base
4. a strong acid or a base

Answer

either a weak acid or a weak base

Explanation

An acid-base indicator is an organic dye that is chemically either a weak acid or a weak base. It changes color depending on the pH of the solution it is in, due to the ionization of the acidic or basic functional group in the molecule.

Question 18

Acid turns a blue litmus paper to

1. red
2. deep violet
3. green
4. colourless

Answer

red

Explanation

An acid turns a blue litmus paper red. Litmus paper is a pH indicator that changes colour depending on the pH of the solution it is in, with red indicating acidity and blue indicating basicity.

Question 19

Phenolphthalein is a suitable indicator for titration between

1. weak acid and weak base
2. weak base-strong acid
3. strong acid-strong base
4. both strong acid-strong base and weak acid-strong base

Answer

both strong acid-strong base and weak acid-strong base

Explanation

Phenolphthalein is a suitable indicator for titration between a weak acid and a strong base or a weak base and a strong acid. It changes color in the pH range of 8.2-10.0, which is suitable for these types of titrations. It is not suitable for titrations between strong acids and strong bases.

Question 20

By acid rain, the pH of the water body

1. is reduced
2. is increased
3. remains the same
4. none

Answer

reduced

Explanation

By acid rain, the pH of the water body is reduced. Acid rain is rainwater that has a pH of less than 5.6 due to the presence of sulfur dioxide and nitrogen oxides, which react with water in the atmosphere to form sulfuric acid and nitric acid. When this acidic rainwater enters lakes, rivers, and other water bodies, it can lower their pH and make them more acidic, which can harm aquatic plants and animals.

Answer in one word or in one sentence

[Each of Mark-1]

Question

1. What is an acid?
2. What is a base ?
3. What is a salt ?
4. What is a strong acid (or base) ?
5. Define pH.
6. What is the pH value of neutral water at 25°C.
7. What is a neutralization reaction?
8. Give example of each: (i) strong acid, (ii) strong base (iii) weak acid (iv) weak base.
9. What is an indicator?
10. Are two solutions, 1.0 M HCI and 1.0 M CH₃COOH, equally strong?
11. Do the solutions 1.0 M HCI and 1.0 M CH₃COOH have same pH?
12. What is ‘titration’?
13. On addition of 2 drops of methyl orange, what colour a NaOH solution will develop?
14. How many acidic protons are there in each : (i) CH₃COOH, (ii) H₂SO₄ (iii) Na₂CO₃ (iv) NaHCO₃ (v) H₂CO₃
15. What is an amphoteric salt?

Answer

1. Acid is a compound that donates a proton.
2. A base is a compound that accepts a proton.
3. Salt is a compound formed from the reaction of an acid and a base.
4. A strong acid (or base) is a substance that completely ionizes in water.
5. pH is a measure of the acidity or basicity of a solution.
6. pH value of neutral water at 25°C is 7.
7. A neutralization reaction is a chemical reaction between an acid and a base that forms salt and water.
8. Examples: (i) HCl (ii) NaOH (iii) CH₃COOH (iv) NH₃
9. An indicator is a substance that changes colour depending on the pH of a solution.
10. No, they are not equally strong.
11. No, they do not have the same pH.
12. Titration is a method of determining the concentration of a solution by reacting it with a solution of known concentration.
13. NaOH solution will develop a yellow colour with the addition of methyl orange.
14. (i) 1 (ii) 2 (iii) 0 (iv) 1 (v) 2
15. Amphoteric salt is a salt that can act as both an acid and a base.

Short answer type questions

[Each of Mark-2]

Question 1

Explain how a salt is produced by partial replacement of hydrogen from H₂S. Is the salt is an acidic salt on a basic salt ?

Answer

When the hydrogen atoms in H₂S are partially replaced with a metal cation, a salt is formed. This salt is generally an acidic salt due to the acidic nature of H₂S.

Question 2

Balance the following equation:

1. Na₂O₂ + H₂O→ NaOH + O₂;
2. Cl₂+ NaOH → NaCl + NaClO₃ + H₂O;
3. Cu + HNO₃ → Cu(NO₃)₂ + NO₂ + H₂O.

Answer

1. Na₂O₂ + 2H₂O→ 2NaOH + O₂;
2. Cl₂+ 2NaOH → NaCl + NaClO₃ + H₂O;
3. 3Cu + 8HNO₃ → 3Cu(NO₃)₂ + 2NO₂ + 4H₂O.

Question 3

What is neutralization? Give example.

Answer

Neutralization is a chemical reaction between an acid and a base that produces a salt and water. An example is the reaction between hydrochloric acid and sodium hydroxide to form sodium chloride and water.

Question 4

Give example of a neutral oxide and an acidic oxide made from the same element.

Answer

Carbon monoxide (CO) is a neutral oxide because it does not react with water to form an acid or a base.

Carbon dioxide (CO₂), on the other hand, is an acidic oxide because it reacts with water to form carbonic acid.

Question 5

How would you distinguish between solutions of sodium carbonate and solution of sodium bicarbonate by using indicator ?

Answer

A solution of sodium carbonate will turn phenolphthalein pink, indicating a basic solution. A solution of sodium bicarbonate will turn methyl orange yellow, indicating a slightly acidic solution.

Question 6

An acid forms one acid salt and one normal salt. What is the basicity of the acid?

Answer

The basicity of the acid is 2. An acid that forms one acid salt and one normal salt donates two hydrogen ions per molecule. Therefore, its basicity is 2.

Question 7

1. NaCl + Water + X (indicator) → Orange colour; X = ?;
2. Na₂CO₃ + Water + Y (indicator) → Reddish violet ; Y = ?

Answer

X = phenolphthalein; Y = methyl orange.

Question 8

State why potassium bicarbonate is called an acidic salt? Give another example of this type.

Answer

Potassium bicarbonate is called an acidic salt because it is formed by the partial neutralization of an acid (carbonic acid) with a weak base (potassium hydroxide), resulting in an ion that has acidic properties. Another example of this type is sodium dihydrogen phosphate (NaH₂PO₄).

Question 9

Mention at least two points to distinguish between an acid and a base. 

Answer

1. Acids donate protons while bases accept protons.
2. Acids turn blue litmus paper red while bases turn red litmus paper blue.

Question 10

Aqueous solution of CO₂ is acidic or basic or neutral ? How would you show that?

Answer

Aqueous solution of CO₂ is weakly acidic. This can be shown by adding an indicator such as bromothymol blue, which will turn yellow in an acidic solution, to the CO₂ solution and observing the colour change.

Question 11

1. Which acid produces brown fumes on heating ?;
2. Which gas is evolved by the reaction of common salt with concentrated H₂SO₄ ?

Answer

The acid that produces brown fumes on heating is nitric acid (HNO₃). This is due to the decomposition of the acid into nitrogen dioxide (NO₂) gas, which has a brown colour.

The gas evolved by the reaction of common salt (NaCl) with concentrated H₂SO₄ is hydrogen chloride (HCl) gas. This is due to the reaction between sodium chloride and sulfuric acid to form hydrogen chloride gas and sodium bisulfate (NaHSO₄) salt.

Question 12

What is aqua regia ? Mention one use of it.

Answer

Aqua regia is a 1:3 mixture of concentrated nitric and hydrochloric acids that can dissolve noble metals such as gold and platinum. It is used for metal analysis and in the purification of metals.

Question 13

How many gram of HCl will be required to completely neutralize 80 g of NaOH ? (H. = 1, O 16, Na 23, Cl = 35.5)

Answer

The balanced chemical equation for the reaction between HCl and NaOH is:

HCl + NaOH → NaCl + H2O

The molar mass of NaOH is 40 g/mol. Therefore, 80 g of NaOH is equal to 2 moles of NaOH.

The equation shows that 1 mole of HCl reacts with 1 mole of NaOH. Therefore, 2 moles of HCl are required to neutralize 2 moles of NaOH.

The molar mass of HCl is 36.5 g/mol. Therefore, 2 moles of HCl is equal to 73 g of HCl.

Hence, 73 g of HCl will be required to completely neutralize 80 g of NaOH.

Question 14

Write with balanced chemical equation what happens in the reaction of iron with dilute hydrochloric acid.

Answer

The reaction of iron (Fe) with dilute hydrochloric acid (HCl) produces iron chloride (FeCl2) and hydrogen gas (H2).

Fe + 2HCl → FeCl₂ + H₂

Question 15

Using barium chloride solution, how will you identify which bottle contains H₂SO₄ out of three bottles containing HCl, H₂SO₄ and HNO₃, respectively?

Answer

To identify which bottle contains H₂SO₄ using barium chloride solution, we can follow these steps:

1. Add a few drops of barium chloride solution to a small amount of each acid in separate test tubes.
2. If H₂SO₄ is present, a white precipitate of barium sulfate (BaSO₄) will form in the test tube containing H₂SO₄.
3. The test tube containing HCl or HNO₃ will not show any reaction with the barium chloride solution.

Therefore, the bottle containing H₂SO₄ can be identified by the formation of a white precipitate of barium sulfate in the test tube containing the acid.

Long answer type questions

[Each of Mark-3]

Question 1

H₂S cannot be dried by using concentrated H₂SO₄-explain why with balanced equations.

Answer

H₂S cannot be dried by using concentrated H₂SO₄ because H₂SO₄ reacts with H₂S to form sulfur and water, which can lead to the formation of a highly explosive mixture of sulfur dioxide and hydrogen sulfide. The balanced chemical equation for this reaction is:

H₂SO₄ + H₂S → 2H₂O + S

As seen in the equation, the reaction between H₂SO₄ and H₂S leads to the formation of water and elemental sulfur. Therefore, H₂SO₄ cannot be used to dry H2S gas as it will not remove moisture and can lead to the formation of a hazardous mixture.

Question 2

A glass rod moistened with con. HCl is introduced in a full of gas. White fumes are produced. Identify the gas in the jar. What is the compound giving fume? Give equation.

Answer

The white fumes produced when a glass rod moistened with concentrated HCl is introduced into a jar of gas are due to the formation of hydrochloric acid (HCl) gas. The gas in the jar could be ammonia (NH₃), which reacts with HCl gas to form a white smoke of ammonium chloride (NH₄Cl) salt. The balanced chemical equation for this reaction is:

NH₃ + HCl → NH₄Cl

Therefore, the compound giving white fumes is ammonium chloride (NH4Cl), which is formed by the reaction between ammonia (NH₃) and hydrochloric acid (HCl).

Question 3

State the Arrhenius concept related to acid and base.

Answer

The Arrhenius concept of acids and bases defines an acid as a substance that dissociates in water to produce hydrogen ions (H⁺) and a base as a substance that dissociates in water to produce hydroxide ions (OH^–). According to this concept, an acid is a substance that increases the concentration of H⁺ ions in aqueous solution, while a base is a substance that increases the concentration of OH^– ions in an aqueous solution.

Question 4

Why is Na₂O called a basic oxide but ZnO is called an amphoteric oxide ? Give equations.

Answer

Na2O is called a basic oxide because it reacts with water to form a strong base, sodium hydroxide (NaOH), which increases the pH of the solution. The balanced chemical equation for the reaction between Na₂O and water is:

Na₂O + H₂O → 2NaOH

On the other hand, ZnO is called an amphoteric oxide because it can react as both an acid and a base. It can react with both acids and bases to form salts, and it can also react with water to form both an acidic and basic solution. The balanced chemical equations for the reactions of ZnO with an acid and a base are:

ZnO + 2HCl → ZnCl₂ + H₂O

ZnO + 2NaOH → Na₂ZnO₂ + H₂O

Question 5

What colour will be produced when methyl orange is added to dilute NaOH solution? What colour will be produced at the neutralization point if this solution is neutralized with dilute HCl?

Answer

When methyl orange is added to dilute NaOH solution, the solution will turn yellow.

At the neutralization point when the NaOH solution is neutralized with dilute HCl, the solution will change its color from yellow to orange. This is because methyl orange changes color at a pH range of 3.1 to 4.4, with a transition from yellow to orange. The point at which the solution changes from yellow to orange indicates that the solution has been neutralized, and the pH is around 7, which is the pH of neutral water.

Question 6

A bottle contains dilute HCl solution, a second bottle contains an aqueous solution of caustic soda and a third bottle contains an aqueous solution of NaCl. With the help of a blue litmus paper only, how would you identify the contents of the three bottles?

Answer

To identify the contents of the three bottles using a blue litmus paper only, the following steps can be followed:

1. Take a blue litmus paper and dip it into the solution in the first bottle.
2. If the solution in the first bottle is HCl, the blue litmus paper will turn red due to the acidic nature of HCl.
3. Take another blue litmus paper and dip it into the solution in the second bottle.
4. If the solution in the second bottle is an aqueous solution of caustic soda (NaOH), the blue litmus paper will turn blue due to the basic nature of NaOH.
5. Take a third blue litmus paper and dip it into the solution in the third bottle.
6. If the solution in the third bottle is an aqueous solution of NaCl, the blue litmus paper will remain blue as NaCl is a neutral salt and does not affect the pH of the solution.

Therefore, by using a blue litmus paper, we can identify the contents of the three bottles as follows: Bottle 1 contains HCl, bottle 2 contains an aqueous solution of caustic soda (NaOH), and bottle 3 contains an aqueous solution of NaCl.

Question 7

Write with a balanced chemical equation what happens when: (i) concentrated nitric acid is heated with copper turnings. (ii) aluminium powder is boiled with a concentrated aqueous solution of sodium hydroxide.

Answer

(i) When concentrated nitric acid is heated with copper turnings, nitrogen dioxide (NO2) gas is evolved along with the formation of copper nitrate (Cu(NO3)2) and water (H2O). The balanced chemical equation for the reaction is:

8HNO₃ + 3Cu → 3Cu(NO₃)₂ + 4H₂O + 2NO₂

(ii) When aluminium powder is boiled with a concentrated aqueous solution of sodium hydroxide, hydrogen gas (H₂) evolves along with the formation of sodium aluminate (NaAlO₂) and water (H₂O). The balanced chemical equation for the reaction is:

2Al + 2NaOH + 6H₂O → 2NaAl(O2H)₄ + 3H₂

The reaction produces a lot of heat and hydrogen gas is evolved with effervescence.