Acids, Bases and Salts: 17 MCQs with answers

A · $H^+$

Acids produce hydrogen ions ($H^+$) when dissolved in water; bases produce hydroxide ions ($OH^-$).

C · The liquid is acidic

Blue litmus turning red is the standard test for an acid.

C · Baking soda

Baking soda (sodium bicarbonate) is a mild base; the others are acids.

A · acid + base → salt + water

Neutralisation always produces a salt and water from an acid and a base.

A · True

Acids release $H^+$ ions and bases release $OH^-$ ions when dissolved in water — this single fact explains litmus, pH, and neutralisation.

C · Basic

Phenolphthalein is colourless in acid and pink in base, so pink indicates a basic solution.

D · 100 times

The pH scale is logarithmic: a difference of 2 pH units means $10 \times 10 = 100$ times the $H^+$ concentration.

D · It is a base that neutralises excess stomach acid

Antacids are bases; they neutralise excess hydrochloric acid in the stomach.

B · Strong means fully ionised; concentrated means much dissolved

Strong refers to how completely an acid ionises; concentrated refers to how much is dissolved in a given volume.

C · Sodium chloride

$HCl + NaOH \rightarrow NaCl + H_2O$, so the salt is sodium chloride.

B · Lime

Lime is a base; adding it neutralises some soil acid and raises the pH toward neutral.

C · Basic

Methyl orange is red in acid and yellow in base, so yellow means basic.

A · Acetic acid

Acetic acid is an acid, not a salt. The other three are all salts formed when an acid's hydrogen is replaced.

B · Acidic

A strong acid with a weak base gives an acidic salt; the reverse pairing gives a basic salt.

A · Both A and R are true, and R correctly explains A.

Strong and concentrated are independent properties, so a dilute strong acid and a concentrated weak acid are both possible — R is the correct explanation of A.

D · The liquid is a base

Red litmus turning blue and pH around 10 both indicate a basic solution; the evidence is consistent across three tests.

C · pH 7

The reaction between HCl and NaOH is a neutralization reaction that produces water and sodium chloride. Since both solutions are of equal concentration and volume, they completely neutralize each other, resulting in a neutral solution with a pH of 7.