C4 - Acids and Alkalis

What is an acid?

A substance that produces hydrogen ions (H⁺) in aqueous solution.

What does (aq) mean in a chemical formula?

Aqueous solution (dissolved in water).

Give the formula for hydrochloric acid in solution.

HCl(aq) → H⁺ + Cl⁻

Give the formula for sulfuric acid in solution.

H₂SO₄(aq) → 2H⁺ + SO₄²⁻

Give the formula for nitric acid in solution.

HNO₃(aq) → H⁺ + NO₃⁻

What is a base?

A chemical that neutralises an acid to form a salt and water.

What types of compounds are usually bases?

Metal oxides and metal hydroxides.

What is an alkali?

A base that is soluble in water.

Is copper oxide a base or an alkali?

Copper oxide is a base only (not soluble in water).

Is iron(III) hydroxide a base or an alkali?

Iron(III) hydroxide is a base only (not soluble in water).

Is sodium hydroxide a base or an alkali?

Sodium hydroxide is both a base and an alkali (it is soluble in water).

What ions do alkalis produce in aqueous solution?

Hydroxide ions (OH⁻).

Write the equation for sodium hydroxide in aqueous solution.

NaOH(aq) → Na⁺ + OH⁻

What does the pH scale measure?

How acidic or alkaline a solution is.

What is the pH range of acids?

pH 0-6.

What is the pH of a neutral solution?

pH 7.

What is the pH range of alkalis?

pH 8-14.

How can we measure the pH of a solution?

Using a pH probe or universal indicator.

What colour does universal indicator turn in a neutral solution?

Green.

What colour does universal indicator turn in a strongly acidic solution?

Red.

What colour does universal indicator turn in a strongly alkaline solution?

Purple.

What ions do acids produce in solution?

Hydrogen ions (H⁺).

What ions do alkalis produce in solution?

Hydroxide ions (OH⁻).

What happens in a neutralisation reaction?

Hydrogen ions (H⁺) react with hydroxide ions (OH⁻) to form water.

What is the ionic equation for neutralisation?

H⁺ + OH⁻ → H₂O