Final answer:
To calculate the % change in pH when NaOH is added to a buffer solution, we must first convert the mass of NaOH to moles and determine the new concentrations of the buffer components. Then, using the Henderson-Hasselbalch equation, we find the new pH and compare it to the initial pH to find the percentage change.
Step-by-step explanation:
To find the % change in pH when solid NaOH is added to a buffer solution of HX and NaX with a known acid dissociation constant (Ka), we first need to calculate the number of moles of NaOH and compare the change in concentrations of the buffer components (HX and NaX) after addition of NaOH. Given that the Ka for HX is 2.0 x 10^-5 and the molar mass of NaOH is 39.997 g/mol, we begin by converting the mass of NaOH to moles:
moles NaOH = 4.052 g / 39.997 g/mol = 0.1013 mol
As NaOH is a strong base, it will react completely with HX in the buffer:
HX + NaOH → H2O + NaX
The reaction will consume HX and form more NaX in the buffer. Once we have the new concentrations, we can use the Henderson-Hasselbalch equation to calculate the new pH of the buffer. Then, we can find the % change in pH by comparing the initial and final pH values:
% change in pH = ((final pH - initial pH) / initial pH) x 100
However, the exact calculation cannot be completed without the initial pH or pKa of the buffer solution.