CI 8.1 Acids and Bases

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

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

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

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

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

How are hydroxide ions (OH-) made? NaOH Na+ + OH- CO32- + H2O HCO3- + OH- NH3 + H2O NH4+ + OH-

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

Every acid has a conjugate base Every base has a conjugate acid

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

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-

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

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?

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