Answer:
The pH is 4.76
Explanation:
Step 1: Data given
Volume of a 0.476 M hydrocyanic acid solution = 29.8 mL = 0.0298 L
Volume of 0.487 M barium hydroxide solution = ?
Ka HCN = 6.2 * 10^-10
Step 2: Calculate pH
Hydrocyanic acid is a weak acid.
Barium hydroxide is a strong base.
The question asked = the pH BEFORE any base has been added, so we can ignore the base.
To calculate the pH of aweak acid, we need the pKa
HCN ⇔ H+ + CN-
Ka = [H+][CN-]/[HCN]
⇒ for weak acid: [H+]=[CN-]
Ka = [H+]²/[HCN]
[H+]² = [HCN]*Ka
[H+] = √([HCN]*Ka)
pH = -log(√([HCN]*Ka))
pH = -log(√(0.476 * 6.2*10^-10))
pH = 4.76
The pH is 4.76
