A solution has [H+] = 1.0 x 10-10 M. The pOH of this solution is __________.?

Method 1 :
pH = -log[H⁺] = -log(1.0 × 10⁻¹⁰) = 10.0
pOH = pKw - pOH = 14.0 - 10.0 = 4.0


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Method 2 :
[OH⁻] = Kw / [H⁺] = (1.0 × 10⁻¹⁴) / (1.0 × 10⁻¹⁰) M = 1.0 × 10⁻⁴ M
pOH = -log[OH⁻] = -log(1.0 × 10⁻⁴) = 4.0