Calculate the pH change that occurs when?

Question

1.0 mL of 1.0 M HCl is added to (a) 1.0 L of pure water and (b) 1.0 L if acetic acid/sodium acetate buffer with [CH3COOH] = 0.700 M and [CH3COO--] = 0.600 M.

Answer 1

a) For the first one HCl is a strong acid. So it dissociates completely in water. The equation for the dissociation of HCl is:

HCl(aq) --> H+(aq) + Cl-(aq)

Your given the initial volume and concentration of acid, so from this you can find the number of moles of acid. Divide the moles of acid by the total volume and there you go.

.001L of HCl *(1moles HCl/L) = .001moles of HCl

Molarity = moles/Liter

M= .001moles/1.001L= 9.99*10^-4M= [HCl] = [H+]

pH = -log[H+]

pH = -log(9.99*10^-4)

pH = 3

For this one we can look up the Ka and we know its a buffered solution so we can use the Henderson Hasselbach equation.

CH3COOH Ka =1.8*10^-5

pH = pKa + log(base/acid)

pH = -log(1.8*10^-5) + log(.6M/.7M)

pH = 4.68