7.1 Acids and alkalisWhy are solutions acidic or

alkaline?How do we measure acids?

5 May 2023

Acids Alkalis

7.1 Acids and alkalis• Acids are solutions which produce H+

ions when added to water.• Bases are substances which neutralise

acids.• Alkalis are soluble bases. They

produce OH- ions in water.• The pH scale shows how acidic or

alkaline a solution is.

5 May 2023

Hydrofluoric acid is so corrosive it will dissolve glass. The fluorine ions attack the silicon atoms in the glass!

What are acids and bases?• Acids dissolve in water to produce

Hydrogen (H+) ions. Hydrochloric Acid has the formula HCl.

HCl(g) water H+ (aq) + Cl- (aq)

What do the terms (g), (s) and (aq) mean?• Alkalis dissolve in water to produce

Hydroxide (OH-) ions. Sodium Hydroxide has the formula NaOH.

NaOH(s) water Na+ (aq) + OH- (aq)

Measuring Acidity• Indicators are chemicals which change colour

when added to acids or alkalis. E.g. Litmus, beetroot juice.

• pH goes from 0 = strong acid to 14 = strong alkali. Universal indicator shows the whole range.

Which is the most alkaline?

• Test a number of substances using universal indicator to find the strongest alkaline.

• Record your results in a table with the pH level.

P197 Summary questions.

7.1 Acids and alkalis• Acids are solutions which produce H+

ions when added to water.• Bases are substances which neutralise

acids.• Alkalis are soluble bases. They

produce OH- ions in water.• The pH scale shows how acidic or

alkaline a solution is.

5 May 2023

Hydrofluoric acid is so corrosive it will dissolve glass. The fluorine ions attack the silicon atoms in the glass!