Acids and Bases

Question 1

When dissolved in water, an acid produces:

Accepted Answer

hydrogen ions, H⁺ — An acid is a source of hydrogen ions (H⁺) in aqueous solution.

Question 2

An alkali is a soluble base that produces:

Accepted Answer

hydroxide ions, OH⁻ — Alkalis dissolve in water to give hydroxide ions (OH⁻).

Question 3

The pH of an acidic solution is:

Accepted Answer

less than 7 — Acids have pH below 7; the more acidic, the lower the pH.

Question 4

An acid turns blue litmus paper:

Accepted Answer

red — Litmus is red in acid and blue in alkali, so blue litmus turns red.

Question 5

Which products form when a dilute acid reacts with a reactive metal?

Accepted Answer

salt + hydrogen — acid + metal → salt + hydrogen; the hydrogen gas can be tested with a lit splint (squeaky pop).

Question 6

Which products form when an acid reacts with a carbonate?

Accepted Answer

salt + water + carbon dioxide — acid + carbonate → salt + water + carbon dioxide; the CO₂ turns limewater milky.

Question 7

Neutralisation of an acid by an alkali always produces:

Accepted Answer

a salt and water — H⁺ + OH⁻ → H₂O, so neutralisation forms a salt and water.

Question 8

A strong acid differs from a weak acid because a strong acid is:

Accepted Answer

fully ionised in water — A strong acid ionises completely in water, whereas a weak acid ionises only partly.

Question 9

Universal indicator in a strong acid shows the colour:

Accepted Answer

red — Universal indicator is red at low pH (strong acid) and purple at high pH (strong alkali).

Question 10

A base can best be described as a substance that:

Accepted Answer

neutralises an acid — A base reacts with and neutralises an acid; if soluble it is called an alkali.