Which weak acid should be used to create a buffer at pH= 4.39 \"Lactic Acid, C 3
ID: 1032168 • Letter: W
Question
Which weak acid should be used to create a buffer at pH= 4.39
"Lactic Acid, C3H6O2, Ka = 1.38×10–4"
"Acetic Acid, CH3O2H, Ka = 1.75×10–5"
"Carbonic, H2CO3, Ka = 4.30×10–7"
"Hypochlorous Acid, HOCl, , Ka = 3.50×10–8"
"Hypobromous Acid, HOBr, Ka = 2.00×10–9"
"Chloroacetic Acid, CClH2O2H, Ka = 1.36×10–3"
"Lactic Acid, C3H6O2, Ka = 1.38×10–4"
"Acetic Acid, CH3O2H, Ka = 1.75×10–5"
"Carbonic, H2CO3, Ka = 4.30×10–7"
"Hypochlorous Acid, HOCl, , Ka = 3.50×10–8"
"Hypobromous Acid, HOBr, Ka = 2.00×10–9"
"Chloroacetic Acid, CClH2O2H, Ka = 1.36×10–3"
Explanation / Answer
A Buffer solution has the ability to resist a pH change in the solution .
A Buffer can be formed by making a mixture of a weak acid and it's Salt with a strong Base .
pH of Buffer can be calculated by using the relation
pH = pKa + log { [ Salt ] / [ Acid ] }
Where Ka is the acid dissociation constant of the Weak acid .
To get a buffer which can be used at pH = 4.39 , we need to take a weak acid whose pKa is around 4.39 , because the Buffeing action of a buffer will be maximum at pH = pKa .
Amongst all the Weak acids ' Acetic acid ' has the Ka = 1.75 x 10-5 , hence it's pKa will be 4.75 which is close to the value of the required pH ( 4.39 ) .
Hence , Acetic Acid can be used to create a Buffer at a pH of 4.39 .
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