Bronstead-Lowry acids and bases
- A Bronstead-Lowry acid is a proton donor.
- A Bronstead-Lowry base is a proton acceptor.
- pH= -log[H+]
- A strong acid means that it is completely dissociated.
- The concentration of hydrogen ions in a monoprotic strong acid will be the same as the concentration of the acid.
- [H+]= 1 x 10^-pH
Ionic product of water
- The equation for the dissociation of water is H20 -> H+ + OH-
- Kw= [H+] [OH-]
- At 25 degrees the value of Kw for all aqueous solutions is 1 x 10^-14 mol2 dm-6
- Weak acids are only slightly dissociated.
- Ka= [H+][A-] [HA]
- pKa= -logKa
- Ka= 10^-pKa
- When a weak acid has been reacted with exactly half the neutralisation volume of alkali we can assume that [H+]= Ka.
- pH= pKa
- A buffer solution is one where the pH does not change significantly if small amounts of acid or alkali are added to it.
- An acidic buffer is made from a weak acid and a salt of that weak acid e.g. ethanoic acid and sodium ethanoate.
- A basic buffer solution is made from a weak base and a salt of that weak base, which is made from reacting the weak base with a strong acid e.g. ammonia and ammonium chloride.
- Buffers are used in shampoos as human hair becomes rough when exposed to alkaline conditions.
- They are also used in biological washing powders…