An aqueous solution contains an unknown concentration of Ba²⁺. When 50 mL of a 1 M solution of Na₂SO₄ is added, BaSO₄ just begins to precipitate. The final volume is 500 mL. The solubility product of BaSO₄ is 1 × 10^–10. What is the original concentration of Ba²⁺ ?

1. 5 × 10^–9 M

2. 2 × 10^–9 M

3. 1 × 10^–9 M

4. 1.0 × 10^–10 M

In aqueous solution, the ionization constants for carbonic acid are
\(K_{1} = 4.2 \times 10^{- 7}\) and \(K_{2} = 4.8 \times 10^{- 11}\)
The correct statement for a saturated 0.034 M solution of the carbonic acid is: