1. Why are solutions acidic or alkaline? How do we measure acids?
7.1 Acids and alkalis
27 April 2017
Why are solutions acidic or alkaline?
How do we measure acids?
Acids
Alkalis

2. 7.1 Acids and alkalis
27 April 2017
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.
Hydrofluoric acid is so corrosive it will dissolve glass. The fluorine ions attack the silicon atoms in the glass!

3. 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)

4. 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.

5. 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.

6. 7.1 Acids and alkalis
27 April 2017
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.
Hydrofluoric acid is so corrosive it will dissolve glass. The fluorine ions attack the silicon atoms in the glass!