What is the order of acidity for #"acetic acid"#, #(H_3C)_2CHCO_2H#, and #H_3C-CH(NO_2)CO_2H#?

1 Answer
anor277
Mar 13, 2016

In order of increasing acidity: #(H_3C)_2CHCO_2H#, #H_3C-CH_2CO_2H#, #H_3C-CH(NO_2)CO_2H#

Explanation:

That is a very tentative order. As a physical scientist you should seek out the data, and find actual #pK_a# values: #pK_a# #=# #4.89# for propanoic acid. If these values are not available (and I could not find the other two easily on the web), this question should not have been asked.

The #pK_a# for acetic acid #=# #4.76#. Thus acetic acid is a slightly stronger acid than propanoic acid in water. Why should this be so?

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