1. Brønsted-Lowry theory of acids and bases An acid is a H + donorHCl A base is a H + acceptorNH 3 H + Cl - + NH 3 Cl - + NH 4 + H + is transferred Note:We often say “Proton”

2. acids and bases in solution HCl H + (aq) + Cl - (aq) HCl + H 2 OH 3 O + (aq) + Cl - (aq) Oxonium Ion

3. Alkalis vs bases NaOH Na + (aq) + OH - (aq) A base is a H + acceptor An alkali is a base that dissolves in water to form hydroxide ions. All alkalis are bases; not all bases are alkalis! CO 3 2- (aq) + H 2 O (l) HCO 3 3- aq) + OH - (aq)

4. Questions: Chemical Ideas page 194 Question 2 d,g,h & 3 b,c (extension: complete remaining parts of 2 &3)

5. Acid-base pairs An acid exists in solution in equilibrium: Overall we call this a conjugate acid-base pair Conjugate acidConjugate base HA (aq) H + (aq) + A - (aq)

6. Acid-base pairs Water can act as an acid OR a base: H 2 O (aq) H + (aq) + OH - (aq) H 3 O + (aq) H + (aq) + H 2 O (aq) Proton donor Proton acceptor We say water is amphoteric

7. Questions: Chemical Ideas page 194 Question 4b & 5b (extension: complete remaining parts of 4 & 5)

8. Strength of acids and bases A weak acid donates protons less easily, however the conjugate base accepts protons more easily than a strong acid HCl (aq) H + (aq) + Cl - (aq) C 2 H 5 OH (aq) H + (aq) + C 2 H 5 O - (aq) A strong acid donates protons easily.

9. Acid-base Indicators Acid base indicators are coloured organic substances that are weak acids. For example: Litmus acid HIn (aq) H + (aq) + In - (aq) base When you add an acid

10. Acid-base Indicators Acid base indicators are coloured organic substances that are weak acids. For example: Litmus acid HIn (aq) H + (aq) + In - (aq) base When you add a base: HIn (aq) + OH- H 2 O (l) + In - (aq)