Question

A buffer solution contains 0.78 mol of hydrogen peroxide (HOOH) and 0.32 mol of sodium hydrogen peroxide (NaOOH) in 7.30 L.
The K_a of hydrogen peroxide (HOOH) is K_a = 2.4e-12. do not round any numbers



(a) What is the pH of this buffer?

pH =  


(b) What is the pH of the buffer after the addition of 0.21 mol of NaOH? (assume no volume change)

pH =  


(c) What is the pH of the original buffer after the addition of 0.19 mol of HI? (assume no volume change)

pH =  

Answer 1

(a) What is the pH of this buffer?

Ka = 2.4 x 10^-12
pKa = 11.6

First calculate the concentration of acid and salt as follows:

Molarity = number of mole s/ volume in L
[acid]= 0.78/ 7.30 =0.11 M

[salt]= 0.32/ 7.30 = 0.04 4 M

pH = pKa + log SALT / acid


pH = 11.6 + log 0.044 /0.11

pH = 11.6 + log 0.4

pH = 11.6 + (-0.39)

= 11.21


(b) What is the pH of the buffer after the addition of 0.21 mol of NaOH? (assume no volume change)

moles acid = 0.78 - 0.21 = 0.57
[acid]= 0.57/ 7.3=0.078 M
moles salt = 0.32 + 0.21 = 0.53
[salt]= 0.53 / 7.3= 0.073
pH = 11.6 + log 0.073 / 0.078

=11.6- 0.031

= 11.569



(c) What is the pH of the original buffer after the addition of 0.19 mol of HI? (assume no volume change)

moles acid = 0.78 +0.19 = 0.97
[acid]= 0.97/ 7.3=0.132M

moles salt = 0.32 -0.19 = 0.13
[salt]= 0.13 / 7.3= 0.0178
pH = 11.6 + log 0.0178 / 0.132

=11.6- 0.87

= 10.73