 Brønsted/Lowry acid: a proton donor proton donor?... a proton is also an H + ion  in water, H 2 O + donated H +  H 3 O +  H 3 O + = “hydronium ion”

 Brønsted/Lowry base: a proton acceptor proton acceptor?... any substance that will take an H + ion  in water, H 2 O+ base  OH - + Hbase

 Acid 1 + Base 1  Acid 2 + Base 2  For weak acids and weak bases  Note the double arrow!

 Acid 1  H + + Base 2  Acid 1 donates H + and becomes Base 2, its “conjugate base”  H + + Base 1  Acid 2  Base 1 accepts the H + from Acid 1 and becomes Acid 2, its “conjugate acid”

 Examples… HF + H 2 O  F - + H 3 O +  HF donates an H + …so it is an “acid”  H 2 O takes the H + from the HF… so it is the “base”

HF + H 2 O  F - + H 3 O +  Look at the “reverse” reaction  which donates an H + ?...it is an “acid” H 3 O +  which takes the H + from the H 3 O + ?...it is the “base” F -

HF + H 2 O  F - + H 3 O +  HF –a weak acid –becomes F -, a base  H 2 O, acting as a base, becomes H 3 O +,an “acid”  The acid becomes its “conjugate base”  The base becomes its “conjugate acid”

NH 3 + H 2 O  NH OH -  H 2 O donates an H +... So it is an “acid”  NH 3 takes the H + from the H 2 O… so it is the “base”

NH 3 + H 2 O  NH OH -  H 2 O–a weak acid –becomes OH -, a base  NH 3, acting as a base, becomes NH 4 +,an “acid”  The acid becomes its “conjugate base”  The base becomes its “conjugate acid”

A weak acid + A weak base Their conjugate acid and base Remember… Weak acids lose an H + and become their conjugate bases Weak bases gain an H + and become their conjugate acids

 …that H 2 O was listed as an acid, and as a base, but a pure H 2 O solution has pH = 7?  H 2 O can act as an acid (lose an H + ) or a base (accept an H + ) depending on what it is combined with  AMPHOTERIC : act as an acid when with a base; act as a base when with an acid