Question -  The pH of 0.1 M monobasic acid is 4.50. Calculate the concentration of H+, A- and HA. Also determine the values of ka and pka of mono basic acid.

Dear Student,

The pH of 0.1 M monobasic acid is 4.50. Calculate the concentration of H+, A- and HA. Also determine the values of ka and pka of mono basic acid.

As we know that pH = -log[H+] = 4.5

[H+] = Antilog [-4.5]

[H+] = 3.16*10-5

HA H+ + A-

[H+] = 3.16*10-5 = [A-]

 HA H+ + A-

Initial conc.  0.1  0  0

At eq.  [HA] = (0.1-3.16*10-5)

0.1>>3.16*10-5

So 3.16*10-5 can be neglected in comparison to 0.1

So [HA] = 0.1 mol

Ka = [H+] [A-] / [HA]

Ka = (3.16*10-5 )2/0.1 = 1.0* 10-8 

pKa = -log Ka

pKa =  -log (1.0* 10-8 )

pKa = 8

Hope it helps!

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