Question

Calculate the ph of a solution formed by mixing 200.0 ml of 0.30 m hclo with 300.0 ml of 0.20 m kclo. the ka for hclo is 2.9 × 10-8. 7.06 8.01 5.99 6.46

Answer 1

c(HClO) = 0,3 M.
V(HClO) = 200 mL = 0,2 L.
n(HClO) = c(HClO) · V(HClO).
n(HClO) = 0,06 mol.
c(KClO) = 0,2 M.
V(KClO) = 0,3 L.
n(KClO) = 0,06 mol.
V(buffer solution) = 0,2 L + 0,3 L = 0,5 L.
ck(HClO) = 0,06 mol ÷ 0,5 L = 0,12 M.
cs(KClO) = 0,06 mol ÷ 0,5 L = 0,12 M.
Ka(HClO) = 2,9·10⁻⁸.
This is buffer solution, so use Henderson–Hasselbalch equation: 
pH = pKa + log(cs ÷ ck).
pH = -log(2,9·10⁻⁸) + log(0,12 M ÷ 0,12 M).
pH = 7,54 + 0.
pH = 7,54