Acids, Bases and Salts

Class 10 Science • Important Questions

Exam Focus: Indicators, reactions of acids and bases, neutralisation, hydronium ions, pH, everyday applications of pH, salts, chlor-alkali process and important compounds.

A. Very Short Answer Questions

Question 1

What is an indicator?

An indicator is a substance that shows an observable change, such as colour or odour, depending on whether a medium is acidic or basic.

Question 2

What colour does blue litmus turn in an acidic solution?

Blue litmus turns red in an acidic solution.

Question 3

What ion is responsible for acidic character in aqueous solution?

Hydronium ions, H₃O⁺, or hydrogen ions represented as H⁺(aq), are responsible for acidic character in aqueous solution.

Question 4

What ion is produced by bases in water?

Bases produce hydroxide ions, OH⁻, in aqueous solution.

Question 5

What is the pH of a neutral solution?

A neutral solution has a pH of 7.

B. Chemical Reactions

Question 6

Write the reaction of zinc with hydrochloric acid.

Zn + 2HCl → ZnCl₂ + H₂

Question 7

What products are formed when a metal carbonate reacts with an acid?

Salt, carbon dioxide and water are formed.

Question 8

Write the reaction between sodium carbonate and hydrochloric acid.

Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂

Question 9

Define neutralisation reaction with an equation.

A reaction between an acid and a base producing salt and water is called neutralisation.

HCl + NaOH → NaCl + H₂O

C. pH and Strength

Question 10

Solution A has pH 3 and solution B has pH 6. Which one is more acidic?

Solution A is more acidic because its pH is lower.

Question 11

Why does an acid conduct electricity in aqueous solution?

Acids produce ions in aqueous solution. These ions carry electric charge and allow the solution to conduct electricity.

Question 12

Why does dry HCl gas not change the colour of dry blue litmus?

HCl shows acidic character when it produces ions in the presence of water. Dry HCl gas does not provide the aqueous medium needed for this ionisation.

Question 13

Differentiate between a strong acid and a weak acid.

At the same concentration, a strong acid produces a relatively larger concentration of hydrogen/hydronium ions than a weak acid.

D. Reasoning Questions

Question 14

Why should acid always be added to water during dilution?

Mixing concentrated acid with water releases considerable heat. Adding acid slowly to water with stirring helps control the heat and reduces the danger of sudden splashing.

Question 15

Why are metallic oxides called basic oxides?

Many metallic oxides react with acids to form salt and water, showing basic character.

Question 16

Why can toothpaste help protect teeth from acid-related decay?

Many toothpastes are basic and can help neutralise excess acids in the mouth. Tooth decay is associated with sufficiently low pH in the mouth.

Question 17

Why is baking soda useful for relieving a bee sting?

Bee sting introduces an acidic substance. Baking soda is a mild base and can help neutralise the acid.

E. Salts and Important Compounds

Question 18

What is the chlor-alkali process?

It is the electrolysis of aqueous sodium chloride (brine), producing sodium hydroxide, chlorine and hydrogen.

Question 19

Write the chemical formula of baking soda.

NaHCO₃.

Question 20

Write the chemical formula of washing soda.

Na₂CO₃·10H₂O.

Question 21

What is water of crystallisation?

It is the fixed number of water molecules present in one formula unit of a salt.

Question 22

What is Plaster of Paris?

Plaster of Paris is calcium sulphate hemihydrate, CaSO₄·½H₂O, obtained by heating gypsum.

F. Competency-Based Practice

Question 23

Solution A has pH 6 and solution B has pH 8. Which solution has a higher concentration of hydrogen ions? Identify the nature of both solutions.

Solution A has the higher hydrogen ion concentration because lower pH corresponds to higher hydronium ion concentration. A is acidic and B is basic.

Question 24

A white precipitate is obtained when carbon dioxide is passed through lime water. Identify the precipitate and explain its formation.

The precipitate is calcium carbonate.

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

Question 25

A student mixes concentrated acid with water by adding water directly to the acid. Explain why this procedure is unsafe.

The dilution is highly exothermic. Sudden heat generation can cause the mixture to splash and may cause burns or even damage the glass container.

G. Long Answer Questions

Question 26

Explain the important chemical properties of acids.

Acids can react with metals to produce salt and hydrogen, with metal carbonates and hydrogencarbonates to produce salt, carbon dioxide and water, and with bases in neutralisation reactions to produce salt and water.

Many metallic oxides also react with acids to form salt and water.

Question 27

Explain the preparation and uses of sodium hydroxide, bleaching powder, baking soda and washing soda.

Sodium hydroxide is produced by electrolysis of brine.

Bleaching powder is produced by the action of chlorine on dry slaked lime.

Baking soda is sodium hydrogencarbonate and is used in baking, antacids and certain fire extinguishers.

Washing soda is sodium carbonate decahydrate and is used in several industrial and domestic applications.

Official Practice Resources

For additional curriculum-aligned preparation, refer to official NCERT and CBSE resources.

NCERT Official Chapter PDF → CBSE Assessment Resources →