# Acid Base Equilibria

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• A Bronstead-Lowry acid is a proton donor.
• A Bronstead-Lowry base is a proton acceptor.

Calculating pH

• pH= -log[H+]

Strong acids

• 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

• Weak acids are only slightly dissociated.
• Ka= [H+][A-]         [HA]
• pKa= -logKa
• Ka= 10^-pKa

Half Equivalence

• When a weak acid has been reacted with exactly half the neutralisation volume of alkali we can assume that [H+]= Ka.
• pH= pKa

Buffer solutions

• 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…