Acids, Bases and Salts — Class 10 MCQs with Answers

Acids, Bases and Salts — important questions & MCQs with answers (Class 10 Science (Chemistry))

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

1. Q1 of 6Easy

   The pH of a neutral solution is:

   A0B7C10D14
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   Answer: 7

   Explanation: On the 0–14 pH scale, 7 is neutral. <7 acidic, >7 basic.

2. Q2 of 6Easy

   Acid + active metal usually produces:

   ASalt + hydrogen gasBSalt + waterCSalt + oxygenDOnly water
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   Answer: Salt + hydrogen gas

   Explanation: Metal + acid → salt + hydrogen gas, e.g. Zn + 2 HCl → ZnCl₂ + H₂↑; oxygen or plain water are not the typical products of this reaction.

3. Q3 of 6Medium

   Onion paste is an example of:

   ApH paperBOlfactory indicatorCLitmusDUniversal indicator
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   Answer: Olfactory indicator

   Explanation: Onion paste loses its odour in basic solutions — an olfactory indicator signals acids or bases by a change in smell.

4. Q4 of 6Medium

   Assertion (A): Dry HCl gas does not change the colour of dry blue litmus paper. Reason (R): Hydrogen ions in HCl are produced only in the presence of water.

   ABoth A and R are true and R is the correct explanation of ABBoth A and R are true but R is not the correct explanation of ACA is true but R is falseDA is false but R is true
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   Answer: Both A and R are true and R is the correct explanation of A

   Explanation: Both are true. H⁺ ions cannot separate from HCl molecules without water, and without H⁺ ions dry HCl gas shows no acidic behaviour.

5. Q5 of 6Hard

   Which is an amphoteric oxide?

   ANa₂OBAl₂O₃CMgODCO₂
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   Answer: Al₂O₃

   Explanation: An amphoteric oxide reacts with both acids and bases; Al₂O₃ does this, unlike the purely basic oxides Na₂O and MgO or the purely acidic oxide CO₂.

6. Q6 of 6Hard

   Assertion (A): If 10 mL of an NaOH solution is completely neutralised by 8 mL of an HCl solution, then 20 mL of the same NaOH solution needs 8 mL of the same HCl solution. Reason (R): In neutralisation, H⁺(aq) ions from the acid combine with OH⁻(aq) ions from the base to form water.

   ABoth A and R are true and R is the correct explanation of ABBoth A and R are true but R is not the correct explanation of ACA is true but R is falseDA is false but R is true
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   Answer: A is false but R is true

   Explanation: A is false: twice the volume of NaOH has twice the OH⁻ ions, so it needs 8 × 2 = 16 mL of the HCl solution. R is true.

Acids, Bases and Salts notes: key concepts (Class 10 Science (Chemistry))

Acids give hydrogen ions in water and bases give hydroxide ions, and the pH scale measures how many. This chapter covers indicators, neutralisation, the reactions of acids and bases, and the preparation and uses of important salts.

Acid

A substance that produces hydrogen ions (H⁺) in aqueous solution, tastes sour and turns blue litmus red.

Base and alkali

A base produces hydroxide ions (OH⁻) and turns red litmus blue; an alkali is simply a base that dissolves in water.

Indicator

A substance that changes colour with acidity — litmus, methyl orange and phenolphthalein are the common ones.

Olfactory indicator

A substance whose SMELL changes in acid or base, such as onion or vanilla essence, used to test solutions without sight.

Neutralisation

The reaction of an acid with a base to give salt and water only, in which the acidic and basic properties cancel.

Reaction of acids with metals

Acids react with active metals to release hydrogen gas, identified by the pop sound with a burning splint.

Reaction with carbonates

Acids react with carbonates and hydrogencarbonates to give carbon dioxide, which turns lime water milky.

pH scale

A scale from 0 to 14 measuring hydrogen-ion concentration: below 7 acidic, exactly 7 neutral, above 7 basic.

Strong and weak acids

Strong acids ionise completely in water and weak acids only partially, so strength differs from concentration.

pH in everyday life

Tooth decay below pH 5.5, acid rain below pH 5.6, and the use of antacids and lime to correct excess acidity.

Water of crystallisation

Fixed water molecules within a salt's crystal structure, as in copper sulphate pentahydrate, CuSO₄·5H₂O.

Common salt and its products

Sodium chloride is the raw material for sodium hydroxide, bleaching powder, baking soda and washing soda.

Bleaching powder, baking soda and washing soda

Ca(OCl)Cl for bleaching and disinfecting, NaHCO₃ in baking and antacids, and Na₂CO₃·10H₂O for softening hard water.

Plaster of Paris

CaSO₄·½H₂O, made by heating gypsum to 373 K; it sets hard with water and is used for plaster casts.