Answer to Question #262379 in General Chemistry for Mule

Question

If 70 mL of 0.01M HCL is added to 150 mL of 0.1M acetic acid, pH 5.0, what is the resulting pH? Identify the appropriate acid and conjugate base and determine their concentrations in the final solution. 

Answer 1

Since we have initial pH of acetic acid before addition of HCl (pH=5.0)

We need to calculate the initial concentration of H3O+ ions

We know pH = 5.0 = -log [H₃O⁺]

[H₃O⁺] = 10^-pH

= 10^-5.0

= 0.00001 mol

What is the [H3O+] in the HCl added

Since HCl dissociates as;

HCl + H₂O = H₃O⁺ + Cl-

Moles of HCl = moles of H₃O⁺

0.01mol were in 1000mL

How many moles will be in 70mL

$\dfrac{0.01mol x 70mL}{1000mL} = 0.0007mol$

Total [H3O⁺] = 0.00001mol + 0.0007mol = 0.00071mol

new pH = -Log(0.00071)

=3.15