Acids and Bases

What is an acid?

A molecule that dissociates in water to form hydrogen ions (H⁺).

What is an alkali?

A base that dissolves in water to produce hydroxide ions (OH⁻).

What ion do acids produce in aqueous solution?

H⁺ (hydrogen ions).

What ion do alkalis produce in aqueous solution?

OH⁻ (hydroxide ions).

Effect of acids on litmus paper?

Turn blue litmus red.

Effect of alkalis on litmus paper?

Turn red litmus blue.

What does the pH scale measure?

Hydrogen ion concentration.

pH < 7 means?

Acidic.

pH = 7 means?

Neutral.

pH > 7 means?

Alkaline.

What is a strong acid?

One that dissociates completely in water to form H⁺ ions.

What is a weak acid?

One that dissociates partially in water to form H⁺ ions.

What is a strong alkali?

One that dissociates completely in water to form OH⁻ ions.

What is a weak alkali?

One that dissociates partially in water to form OH⁻ ions.

What is neutralisation?

A reaction between H⁺ ions and OH⁻ ions to form water.

What is a salt?

Product of neutralisation of an acid and a base.

What makes up a salt?

Cation (from base) + Anion (from acid)

What do acids react with metals to form?

Salt + hydrogen gas.

What do acids react with carbonates to form?

Salt + carbon dioxide + water.

What do acids react with bases to form?

Salt + water.

What do alkalis react with ammonium salts to form?

Salt + ammonia + water.

Why is water important for acids?

Acids only dissociate and form H⁺ ions in water.

What is an acidic oxide?

Non-metal oxide that neutralises a base.

What is a basic oxide?

Metal oxide that neutralises an acid.

What is a neutral oxide?

Oxide showing neither acidic nor basic properties.

What is an amphoteric oxide?

Metal oxide that reacts with both acids and bases.

How is excess soil acidity treated?

By adding calcium carbonate (liming).

What ions are produced by alkalis in water?

OH⁻ ions.

Write the ionic equation for neutralisation.

H⁺ + OH⁻ → H₂O

A solution has pH 3. Acidic, neutral, or alkaline?

Acidic.

What happens when an acid reacts with a carbonate?

Salt + carbon dioxide + water are formed.

What type of oxide is Al₂O₃?

Amphoteric oxide.

What is produced when an alkali reacts with ammonium salts?

Salt + ammonia gas + water.

What is neutralisation in words?

The reaction between hydrogen ions and hydroxide ions to form water.