Question

BONUS QUESTION

Answer 1

Answer:

pH = 12.5

Explanation:

The reaction that takes place is

• 2OH⁻(aq) + Pb⁺²(aq) → Pb(OH)₂(s)

The OH⁻ species come from the metal hydroxide of the solution, and Pb(OH)₂ is the precipitate.

Now we convert 3.81 grams of Pb(OH)₂ into moles, using its molar mass:

• 3.81 g ÷ 241.12 g/mol = 0.0158 mol Pb(OH)₂

Now we convert 0.0158 Pb(OH)₂ moles into OH⁻ moles, using the stoichiometric coefficients of the reaction:

• 0.0158 mol Pb(OH)₂ * $\frac{2molOH^-}{1molPb(OH)_2}$ = 0.0316 mol OH⁻

With the given concentration (1 L), we calculate [OH⁻]:

• [OH⁻] = 0.0316 mol / 1 L = 0.0316 M

Then we calculate the pOH of the solution:

• pOH = - log[OH⁻] = 1.5

And finally we calculate the pH:

• pH = 14 - pOH

• pH = 12.5