1. CI 8.1 Acids and Bases

2. Acids Turn litmus red Neutralised by bases pH < 7
Liberate CO2 from carbonates

3. BrØnsted-Lowry Theory
An acid is an H+ donor
A base is an H+ acceptor
H+Cl- + NH3  Cl- + NH4+

4. The oxonium ion An acid reacts with water to form oxonium ions
HCl + H2O  H3O+ + Cl-
Water is acting as a base

5. The oxonium ion H H+ x O x
What type of bond is this? H

6. Is there a difference between an alkali and a base?
A base is a substance which accepts H+ ions
Alkali = a base which forms OH- ions in water

7. How are hydroxide ions (OH-) made?
NaOH Na OH-
CO H2O HCO3- + OH-
NH H2O NH4+ + OH-

8. Acid – base pairs CH3COOH CH3COO- + H+
CH3COO- + H+ CH3COOH The ethanoate ion can behave as a base; it is the conjugate base of ethanoic acid.
HA H+ + A-
Conjugate base
Conjugate acid

9. Every acid has a conjugate base
Every base has a conjugate acid

10. Amphoteric substances
Water can act as either an acid or a base
With a strong acid it acts as a base
With a strong base it acts as an acid
A substance which behaves in this way is said to be amphoteric

11. Water as an amphoteric substance
Water in the presence of a strong acid: H3O+ H H2O
Water in the presence of a strong base: H2O H OH-

12. Strength of acids and bases
A strong acid is a powerful H+ donor; it is fully dissociated
A weak acid is a moderate or weak H+ donor; it is weakly dissociated
A strong acid has a weak conjugate base and vice versa

13. Indicators Coloured organic substances Weak acids
Conjugate acid and conjugate base forms are different colours
e.g. litmus: HIn H+ + In- red blue
Which is the acid form?

14. Addition of acid In- + H3O+ HIn + H2O The blue litmus turns red
What is the equation for addition of alkali?