Calculation of pH after Titration of Weak Acid: Calculation of pH after Titration of Weak Acid:...

Calculation of pH after Titration of Weak Acid: Calculation of pH after Titration of Weak Acid: A compound has a p K a of 7.4. To 100 mL of a 1.0 M solution of this compound at pH 8.0 is added 30 mL of 1.0 M hydrochloric acid. What is the pH of the resulting solution?

Can you explain what to do after 3.98 = A/HA

Expert Solution

moles of HCl in 30ml of 0.1 = molarity* Volume (L)= 0.1*30/1000 =0.003 moles of acid in 100ml of 1M= 1*100/1000=0.1M

given pH= pKa+ log[A-]/[HA] where A- is conjugate base and HA is acid

8= 7.4 + log[A-]/[HA]

log [A-]/[HA] =0.6

[A-]/[HA] =3.98 , A- =3.98[HA]

A+ [HA] =1

4.98HA= 1, [HA] =1/4.98= 0.200

[A-] = 3.98*0.2 = 0.796 M

now : moles : [A-] =0.796*0.1= 0.0796, [HA]= 0.2*0.1=0.02 HCl =0.003

The addition of HCl (which ionizes completely) leads to formation of more HA.

moles of HA formed = 0.003+0.0796=0.799, moles of A- remaining = 0.0796-0.003= 0.793

now pH= 7.4+ log [0.793/130/(0.799/130) = 7.4+ log (0793/0.799)=7.396

queen_honey_blossom answered 2 years ago

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