UNIT – 2 : ACIDS, BASES AND SALTS(questions)

UNIT – 2 : ACIDS, BASES AND SALTS

Learning Points

Physical properties of acids and bases
Chemical properties of acids and bases
Strength of acid and base solutions
Importance of pH in daily life
More about salts and their uses

I. Multiple Choice Questions (1 mark each)

The chemical equation that represents neutralisation reaction among the following is
(A) BaCl₂ + H₂SO₄ → BaSO₄ + 2HCl
(B) MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂
(C) 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O
(D) AgNO₃ + HCl → AgCl + HNO₃
As the pH value of a neutral solution increases
(A) Basic property decreases and number of OH⁻ ions increases
(B) Acidic property increases and number of H⁺ ions decreases
(C) Basic property increases and number of OH⁻ ions increases
(D) Acidic property decreases and number of H⁺ ions increases
A compound that reacts with both acids and bases to produce salt and water is
(A) Aluminium oxide (B) Copper oxide (C) Iron oxide (D) Sodium oxide
The gas liberated when sodium carbonate reacts with dilute hydrochloric acid is
(A) Carbon dioxide (B) Nitrogen dioxide (C) Hydrogen (D) Chlorine
The substance that converts blue litmus paper to red is
(A) Lime water (B) Pure water (C) Sodium hydroxide solution (D) Gastric juice
The acid present in the stinging hair of nettle leaves is
(A) Methanoic acid (B) Oxalic acid (C) Citric acid (D) Lactic acid
The compound used to remove the permanent hardness of water is
(A) Sodium carbonate (B) Sodium hydroxide (C) Sodium hydrogen carbonate (D) Sodium chloride
The pH value range of an acid is
(A) 0–7 (B) 2–12 (C) 7–14 (D) 12–14
As the number of hydrogen ions increases in a solution, it
(A) Becomes neutral (B) Increases acidity (C) Increases basicity (D) Reduces acidity
The gas released when dilute sulphuric acid is mixed with lead is
(A) Oxygen (B) Nitrogen (C) Hydrogen (D) Carbon
The product obtained when an acid reacts with a metal is
(A) Metal oxide and water (B) Salt and water (C) Metal oxide and hydrogen gas (D) Salt and hydrogen gas
The molecular formula of lime water is
(A) CaO (B) Ca(OH)₂ (C) CaCO₃ (D) CO₂
When hydrochloric acid is added to copper oxide, its colour turns blue-green due to
(A) Copper oxide (B) Water (C) Copper hydroxide (D) Copper chloride
Acid should be added to water, not water to acid, because it is
(A) Exothermic and may explode (B) Endothermic and may explode
(C) Does not mix (D) Mixes very slowly

II. Answer the following (1 mark questions)

What is a neutralisation reaction?
Why should Plaster of Paris be stored in a moisture-proof container?
What are amphoteric oxides?
Can detergents be used to detect permanent hardness of water? Why?
Name the ions responsible for acidic and basic nature of substances.
Write any two uses of washing soda.
1 mL of acetic acid is mixed with 1 mL of sodium hydroxide. Determine the nature of the salt formed.
How is a concentrated acid diluted?
How do you detect an acid using litmus paper?
What is an acid?
Write a chemical equation for the reaction of a metal with a base.
What is the reaction product when air is blown into lime water?
Which gas is released when acids react with metal carbonate or metal hydrogen carbonate?
Why is a metal oxide called a basic oxide?
Why is a non-metal oxide called an acidic oxide?
What are bases?
What ion is formed when an acid dissolves in water?
What happens as the number of hydroxide ions in a solution increases?
What is the pH value of acid rain?
What is the chemical name of baking powder?
Write the chemical equation for preparation of baking powder.
What is baking powder?
Give the molecular formula and name of washing soda.
Which salt is used in fire extinguishers?
Why does baking soda swell when mixed with bread dough?

III. Two-Mark Questions

Give reason: While diluting an acid, acid should be added to water.
Why do agricultural scientists add lime powder to acidic soil?
The pH values of solutions A, B, and C are 5, 6, and 7 respectively. Which is most acidic? Why?
State the properties of acids.
State the properties of bases.
How will you identify distilled water, acid, and base using only red litmus paper?
Why do HCl and HNO₃ show acidic properties but alcohol and glucose do not?
Why does rainwater conduct electricity, but distilled water does not?
What happens to the pH of milk as it curdles? Explain.
A milkman adds a small amount of baking soda to milk.
a) Why does he change pH to slightly alkaline?
b) Why does it take longer to curdle?

IV. Three-Mark Questions

Draw a labelled diagram showing the reaction of zinc granules with dilute sulphuric acid and test for hydrogen gas.
Name the gas liberated when acid reacts with a metal carbonate. Write the reaction and mention the colour of precipitate when this gas is passed through lime water.
Why does sodium chloride solution not change litmus colour, but after electrolysis, red litmus turns blue? Explain with uses.
What is a strong acid? Explain how tooth decay is caused and how it can be prevented.
Write molecular formulae and two uses each of:
(a) Bleaching powder (b) Plaster of Paris
What is a neutralisation reaction? Give one example.
What is the common name of the compound CaSO₄·½H₂O?
How do concentrated acids differ from weak acids? Mention precautions while handling acids.
Name the salts used for:
(a) Removing permanent hardness of water (b) Making water germ-free (c) Supporting fractured bones
Classify the given solutions into acidic and basic. Name the antacid used to neutralise stomach acid.
When red and blue litmus papers are dipped in brine and in the product of its electrolysis, what colour changes occur? Explain.
Observe the pH values of the following solutions and answer:
P – 10.0, Q – 13.7, R – 7.0, S – 1.2
i) Which can be used as antacid? ii) Which pair forms a neutral salt? Why?
Name the acids present in: i) Curd ii) Gastric juice
Four solutions A, B, C, D have pH values 2, 6, 8, 13.
i) Which has more H⁺ and which has more OH⁻ ions? Why?
ii) Which pair can be mixed to get a neutral salt?

V. Four-Mark Questions

Name the products of the chlor-alkali process and write one use of each.
Using NaOH, Ca(OH)₂, H₂ and Cl₂, explain how bleaching powder is prepared. Write its chemical name and one use.
i) How do you identify a basic solution using blue litmus paper?
ii) Under what condition should a farmer treat his soil with slaked lime?
Write the differences between acids and bases.

key answers

I. Multiple Choice Answers (1 mark each)

Q.No	Answer	Explanation
1	✅ (C) 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O	Neutralisation produces salt + water
2	✅ (C) Basic property increases and number of OH⁻ ions increases	Higher pH = more basic
3	✅ (A) Aluminium oxide	Amphoteric oxide reacts with both acids & bases
4	✅ (A) Carbon dioxide	CO₂ gas evolves when acid reacts with carbonate
5	✅ (D) Gastric juice	Contains HCl (acidic)
6	✅ (A) Methanoic acid	Present in nettle leaf sting
7	✅ (A) Sodium carbonate	Removes permanent hardness
8	✅ (A) 0–7	Acidic pH range
9	✅ (B) Increases acidity	More H⁺ → more acidic
10	✅ (C) Hydrogen	Metals + acids → H₂ gas
11	✅ (D) Salt and hydrogen gas	Metal + acid = Salt + H₂
12	✅ (B) Ca(OH)₂	Formula of lime water
13	✅ (D) Copper chloride	Blue-green colour due to CuCl₂ formation
14	✅ (A) Exothermic and may explode	Mixing acid to water releases heat violently

II. 1-Mark Answers

Neutralisation Reaction:
Reaction between an acid and base to form salt and water.
→ HCl + NaOH → NaCl + H₂O
POP storage:
Plaster of Paris reacts with moisture to form gypsum.
Amphoteric oxides:
Oxides reacting with both acids and bases (e.g., Al₂O₃, ZnO).
Detergents & hardness:
Detergents are effective in both hard and soft water.
Ions responsible:
Acid – H⁺, Base – OH⁻
Uses of washing soda:
(a) Removes permanent hardness of water
(b) Used in glass and soap industries
Salt formed:
Sodium acetate – neutral in nature.
Diluting acid:
Always add acid to water slowly, not vice versa.
Detection:
Acid turns blue litmus red.
Acid:
A substance producing H⁺ ions in water (e.g., HCl).
Equation:
2Al + 2NaOH + 6H₂O → 2NaAl(OH)₄ + 3H₂↑
Lime water reaction:
Ca(OH)₂ + CO₂ → CaCO₃ ↓ + H₂O (white precipitate)
Gas released:
CO₂ (Carbon dioxide)
Metal oxide:
Reacts with acid to form salt + water → Basic oxide.
Non-metal oxide:
Reacts with base to form salt + water → Acidic oxide.
Bases:
Substances releasing OH⁻ ions in water.
Ion formed:
H⁺ (Hydronium, H₃O⁺ in water).
Effect:
Solution becomes more basic as OH⁻ increases.
pH of acid rain:
Below 5.6
Baking powder chemical name:
Sodium hydrogen carbonate (NaHCO₃)
Equation:
NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃
Baking powder:
Mixture of baking soda (NaHCO₃) and tartaric acid.
Washing soda:
Na₂CO₃·10H₂O – Sodium carbonate decahydrate.
Fire extinguisher salt:
Sodium bicarbonate (NaHCO₃)
Reason for swelling:
CO₂ released by NaHCO₃ makes dough rise.

III. Two-Mark Answers

Acid dilution reason:
Adding acid to water prevents violent exothermic splashing.
Acidic soil treatment:
Lime (CaO or Ca(OH)₂) neutralises acidic soil (raises pH).
Most acidic solution:
Solution A (pH 5); lower pH = stronger acid.
Properties of acids:

Sour taste
Turn blue litmus red
Conduct electricity

Properties of bases:

Bitter taste, slippery
Turn red litmus blue
Conduct electricity

Litmus test:

Acid: Turns blue → red
Base: No change
Distilled water: No change

Why HCl/HNO₃ acidic:
They release H⁺ ions in water; alcohol/glucose do not.
Rainwater vs distilled water:
Rainwater has dissolved CO₂ → weak acid → conducts current.
Curdling milk:
Lactic acid formation lowers pH.
Baking soda in milk:
(a) Neutralises lactic acid (pH↑)
(b) Slows curdling process.

IV. Three-Mark Answers

Zinc + H₂SO₄ reaction:
Zn + H₂SO₄ → ZnSO₄ + H₂↑
Hydrogen test: Burns with pop sound.
Acid + carbonate:
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑
CO₂ turns lime water milky.
NaCl solution litmus change:
Before electrolysis – neutral (no change);
After – NaOH formed (blue litmus stays blue, red turns blue).
Strong acid & tooth decay:
Bacteria produce acids (pH < 5.5) → enamel damage. Prevent by brushing with basic paste.
Uses:
(a) Bleaching powder: Disinfectant, whitening agent.
(b) Plaster of Paris: For casts, moulds.
Neutralisation:
HCl + NaOH → NaCl + H₂O
Common name of CaSO₄·½H₂O:
Plaster of Paris.
Strong vs weak acids:
Strong → completely ionise (HCl); Weak → partially (CH₃COOH).
Precautions: Wear gloves, goggles, add acid slowly.
Salts:
(a) Na₂CO₃ – Removes hardness
(b) Bleaching powder – Disinfectant
(c) Plaster of Paris – Bone setting
Acidic/basic identification:
Acid (pH <7), base (pH >7).
Antacid: Mg(OH)₂ or baking soda.
Brine electrolysis:
NaCl → NaOH + Cl₂ + H₂
Brine – neutral; product – basic → blue litmus unchanged, red → blue.
Given pH:
i) P(10.0) – Antacid
ii) R(7.0) neutral pair with acid S(1.2).
Acids present:
i) Curd – Lactic acid ii) Gastric juice – Hydrochloric acid
Solutions A(2), B(6), C(8), D(13):

A → Highest H⁺
D → Highest OH⁻
Mix B & C → Neutral salt.

V. Four-Mark Answers

Chlor-alkali process products:
NaOH, H₂, Cl₂

NaOH: Soap industry
H₂: Fuel
Cl₂: Bleaching/disinfectant

Bleaching powder preparation:
Cl₂ + Ca(OH)₂ → CaOCl₂ + H₂O
→ Calcium oxychloride (Bleaching powder)
Use: Disinfect water.
(i) Basic solution turns red litmus → blue.
(ii) Acidic soil → add slaked lime to neutralise.
Difference between Acids & Bases:

Property	Acids	Bases
Taste	Sour	Bitter
Litmus	Blue → Red	Red → Blue
Ion	H⁺	OH⁻
pH	<7	>7

✅ Summary:
This key answer set follows the official KSEAB SSLC 2024–25 LBA evaluation pattern.
For in-person coaching and printed bilingual key booklets, students in Davanagere can visit Skillset Tutorials, Akhtar Raza Circle — expert SSLC Science & Maths coaching.

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