CHEM 1062 Lecture Notes - Lecture 20: Sodium Acetate, Acetic Acid, Conjugate Acid
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Buffer: a solution that contains a mixture of a weak acid and its conjugate base and resists changes in ph by neutralizing. Ch3coo- + h3o+ ch3cooh + h2o. Add h3o+ to ch3coo-, neutralizes the h3o+ . Contains mainly ch3cooh (very weak so it doesn"t dissociate much) Ch3cooh + oh- ch3coo- + h2o. Add oh- to ch3cooh, neutralizes the oh- . Mixture of ch3cooh and ch3coo- (this is a buffer) Contains mostly ions of ch3cooh and ch3coo- Add h3o+, ch3coo- neutralizes it, producing extra ch3cooh. Add oh-, ch3cooh neutralizes it, producing extra ch3coo- Important: as long as the buffer contains enough ch3cooh and ch3coo-, it neutralizes added. H3o+ or oh- without appreciable change in composition (especially ph) Q: find ph of a buffer that has 0. 5 m ch3cooh (ka = 1. 8*10-5) and 0. 50 m ch3coona. 0. 50 +x ~ 0. 50 ~ 0. 50 - x therefore: 1. 8*10-5 = x = [h3o+] ph = -log[h3o+], ph = -log (1. 8*10-5) ph = 4. 74.
