Question

By the addition of 1.2 mole of $H_{2}CO_{3}$ and 0.4 mole of $Na_{2}CO_{3}$ solution is formed. $\left(\right.K_{a_{1}}=4\times \left(10\right)^{- 6}, \, K_{a_{2}}=4\times \left(10\right)^{- 11}\left.\right)$ . Identify the pH of 1 L solution.

• A. 5.4
• B. 7.4
• C. 9
• D. 5.8

Answer 1

Answer: (A)

$H_{2}CO_{3} & + & Na_{2}CO_{3} & \rightarrow & 2NaHCO_{3} \\ 1.2 & & 0.4 & & 0 \\ 0.8 & & 0 & & 0.8$
$pH=-log\left(\right.4\times \left(10\right)^{- 6}\left.\right)+log\frac{0 .8 / 1}{0 .8 / 1}$
pH = 6 - log4 = 5.4