Question

Two solution a and b, each of 100l was made by dissolving 4g of naoh and 9.8g of h2so4 in water, resp. The ph of the resultant solution obtained from mixing 40 l of solution a and 10 l of solution b is

Answer 1

Given:

Mass of NaOH = 4 gm

Mass of H2SO4 = 9.8 gm

Volume of a and b each = 100 L

Volume of a in resultant solution = 40 L

Volume of b in resultant solution = 10 L

To Find:

pH of the resultant solution.

Calculation:

- Molarity of a = 4/(40×100) = 0.001 M

- Molarity of b = 9.8/(98×100) = 0.001 M

- Concentration of OH⁻ = (40 × 0.001 × 1 - 10 × 0.001 × 2)/ (40+10)

⇒ [OH⁻] = 4 × 10⁻⁴

- pOH = - log [OH⁻] = - log (4 × 10⁻⁴)

⇒  pOH = 3.4

- Now, pH of the solution is given as:

pH = 14 - pOH

⇒ pH = 14 - 3.4

⇒ pH = 10.6

- So the pH of resultant solution is 10.6.