Carbonic acid is a diprotic acid, H₂CO₃, with Ka1 = 4.2 × 10⁻⁷ and Ka2 = 4.8 × 10⁻¹¹ at 25°C. The ion product for water is Kw = 1.0 × 10⁻¹⁴ at 25°C. What is the OH⁻ concentration of a solution that is 0.18 M in Na₂CO₃?
a) 6.1 × 10⁻³ M
b) 2.1 × 10⁻⁴ M
c) 6.5 × 10⁻⁵ M
d) 2.9 × 10⁻⁶ M
e) 2.7 × 10⁻⁴ M
