Answer:
The pH change is 0.22.
Step-by-step explanation:
The pKa of the buffer NaHCO3/Na2CO3 is 10.329. To find the pH of this buffer we can use H-H equation:
pH = pKa + log [Na2CO3] / [NaHCO3]
Where pH is the pH of the buffer, pKa is 10.329 and [] could be taken as the moles of each specie.
As the initial volume of the buffer is 1.00L, the initial moles are:
[Na2CO3] = 0.246mol
[NaHCO3] = 0.329mol
Initial pH is:
pH = 10.329 + log [0.246mol] / [0.329mol]
pH = 10.20
The KOH reacts with NaHCO3 as follows:
NaHCO3 + KOH → NaKCO3 + H2O
Where NaKCO3≅ Na2CO3. That means the moles added of KOH are the increasing in moles of KOH and the moles of NaHCO3 that decreases.
Thus, moles after the addition of KOH are:
[Na2CO3] = 0.246mol + 0.072mol = 0.318mol
[NaHCO3] = 0.329mol - 0.072mol = 0.257mol
And pH is:
pH = 10.329 + log [0.318mol] / [0.257mol]
pH = 10.42
The pH change is:
10.42 - 10.20 =
0.22