Question

In: Chemistry

Given that Buffer A contains 200 ml of 0.05 M HOCl and 400 ml 0.03 M...

Given that Buffer A contains 200 ml of 0.05 M HOCl and 400 ml 0.03 M NaOCl, calculate the pH of the buffer solution, the pH of the solution after adding 10 mL of 0.5 M HCl, and the pH of the solution after adding 20 mL of 0.4 M NaOH.

Given that Buffer B contains 200 mL 0.5 HOCl and 400 mL 0.3 M NAOCl, calculate the pH of the buffer solution, the pH of the solution after adding 10 mL of 0.5 M HCl, and the pH of the solution after adding 20 mL of 0.4 M NaOH.

Which buffer will resist pH changes better?

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Expert Solution

pH of acidic buffer

pH = pka + log [salt/acid]

No of moles of HOCl = 200/1000*0.05 = 0.01 mole

No of moles of NaOCl = 400/1000*0.03 = 0.012 mole

pka of HOCl = 7.54

pH = 7.54+log(0.012/0.01) = 7.62

after additing HCl

No of moles of HCl added = (10/1000)*0.5 = 0.005 mole

pH = 7.54+log((0.012-0.005)/(0.01+0.005)) = 7.21

after adding NaOH

No of moles of NaOH added = (20/1000)*0.4 = 0.008 Mole

pH = 7.54+log((0.012+0.008)/(0.01-0.008)) = 8.54

pH of acidic buffer

pH = pka + log [salt/acid]

No of moles of HOCl = 200/1000*0.5 = 0.1 mole

No of moles of NaOCl = 400/1000*0.3 = 0.12 mole

pka of HOCl = 7.54

pH = 7.54+log(0.12/0.1) = 7.62

after additing HCl

No of moles of HCl added = (10/1000)*0.5 = 0.005 mole

pH = 7.54+log((0.12-0.005)/(0.1+0.005)) = 7.58

after adding NaOH

No of moles of NaOH added = (20/1000)*0.4 = 0.008 Mole

pH = 7.54+log((0.12+0.008)/(0.1-0.008)) = 7.68

Buffer solution with higher concentration resists the change in pH better.

queen_honey_blossom answered 5 months ago

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