Question

Weak base BOH has dissociation constant = 10^-8. What is the pH of 0.01 M BOH solution at 25 deg C?

1) 5

2) 4

3) 10

4) 9

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Answer 1

Answer:

the pH of 0.01 m solution at 25 degrees celsius is 5

Answer 2

Given :

Concentration (C) = 0.01 M

Dissociation constant (K) = 10⁻⁸

To Find :

pH of the solution at 25°C

Solution :

In case of weak electrolyte,

    Degree of dissociation ($\alpha$) = $\sqrt{\frac{K}{C} }$

⇒                                         $\alpha$   =  $\sqrt{\frac{10^-^8}{0.01} }$

∴                                          $\alpha$   =  10⁻³ = 0.001

Concentration of OH⁻   =  C$\alpha$

⇒                        [OH⁻]   =  0.01 × 0.001

⇒                        [OH⁻]   = 10⁻⁵ M

Now, pOH = -㏒[OH⁻]

                  =  -㏒ 10⁻⁵

                  = 5

We know, pH + pOH = 14

Therefore, pH = 14 - pOH = 14 - 5 =   9

Hence, the pH of the BOH solution at 25°C is 9.

∴ The correct option is (4) 9