I keep getting these wrong :( A) A buffer solution contains 0.478 M nitrous acid
ID: 1043699 • Letter: I
Question
I keep getting these wrong :(
A) A buffer solution contains 0.478 M nitrous acid and 0.366 M potassium nitrite .
If 0.0508 moles of potassium hydroxide are added to 250 mL of this buffer, what is the pH of the resulting solution ?
(Assume that the volume does not change upon adding potassium hydroxide. ) pH_______
B) A buffer solution contains 0.462 M KHSO3 and 0.257 M K2SO3.
If 0.0155 moles of potassium hydroxide are added to 125 mL of this buffer, what is the pH of the resulting solution ?
(Assume that the volume does not change upon adding potassium hydroxide) _____pH
Ka: 6.20 *10^-8
Explanation / Answer
A)
moles of HNO2 = 0.250 x 0.478 = 0.1195
moles of KNO2 = 0.366 x 0.250 = 0.0915
moles of KOH = 0.0508
pH = pKa + log [salt + C / acid - C]
= 3.25 + log [0.0915 + 0.0508 / 0.1195 - 0.0508]
pH = 3.57
B)
moles of KHSO3 = 0.462 x 0.125 = 0.05775
moles of K2SO3 = 0.125 x 0.257 = 0.0321
moles of KOH = 0.0155
pH = 7.20 + log [0.0321 + 0.0155 / 0.05775 - 0.0155]
pH = 7.25