pH question (1 Viewer)

[Nuendo]

Calculate the pH of a solution produced by mixing 50mL of 0.1mol/L HCl with 20mL of 0.05mol/L NaOH.

 

[Pwnage101]

calculate moles of each:

n(HCl) = n(H+) = cV = 0.1 * 0.05 = 0.005 moles

n(NaOH) = n(OH-) = cV = 0.05 * 0.02 = 0.001 moles

since they react in a 1:1 ratio

there will be excess H+. Quantitatively, this will be: 0.005 - 0.001 = 0.004 moles

thus n(H+) = 0.004 moles after neutralisation
V = 20 + 50 = 70 mL = 0.07L

[H+] = n/V = 0.004/0.07 = 0.057142857

pH = -log[H+] = -log(0.057142857) = 1.243038 = 1.24 (2 dp)

Similar Question was in the 2008 HSC (multiple choice).