Why does #"propane-1-2-3-tricarboxylic acid"# have THREE values of #pK_a# quoted?

1 Answer
anor277
Jan 23, 2018

Why...? Because God it wanted that way...i.e. the acid is POTENTIALLY a triacid with THREE carboxyl groups....

Explanation:

#pK_a# is a measure of acidity...specifically it measures the extent of equilibrium for...

#C_3H_5(CO_2H)_3+H_2OrightleftharpoonsH_3O^+ +C_3H_5(CO_2H)_2(CO_2)^(-)#

#pK_(a1)=3.13#

The acid has two more protons to contribute to aqueous solution....and salts of citrates are common....#pK_(a2)=4.76# (which is the same as that for acetic acid), and #pK_(a3)=6.40#.

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