Question

If you have 100. mL of a 0.100 M TRIS buffer at pH 8.30 and you add 2.00 mL of 1.00 M HCl, what will be the new pH? (The pKa of TRIS is 8.30.)

a) 8.30
b) 8.00
c) 7.80
d) 9.00

Answer 1

The new pH of the buffer solution after adding 2.00 mL of 1.00 M HCl will be 8.00.

Step-by-step explanation:

To determine the new pH of the buffer after adding HCl, we can use the Henderson-Hasselbalch equation. The equation is pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the conjugate base and [HA] is the concentration of the acid. In this case, the initial pH is equal to the pKa, which is 8.30. The initial concentration of the acid, [HA], is 0.100 M, and the concentration of the conjugate base, [A-], is also 0.100 M. When 2.00 mL of 1.00 M HCl is added, it reacts with the conjugate base, converting it into the acid. The new concentration of the acid, [HA], will be 0.100 M + (1.00 M x 0.002 L) = 0.102 M. The concentration of the conjugate base, [A-], will be 0.100 M - (1.00 M x 0.002 L) = 0.098 M. Substituting these values into the Henderson-Hasselbalch equation, we get pH = 8.30 + log(0.098/0.102) = 8.00.