Answer
$pH = 11.774$
Work Step by Step
1. Calculate the molar mass:
40.08* 1 + 16* 1 = 56.08g/mol
2. Calculate the number of moles
$n(moles) = \frac{mass(g)}{mm(g/mol)}$
$n(moles) = \frac{ 0.25}{ 56.08}$
$n(moles) = 4.458\times 10^{- 3}$
3. Find the concentration in mol/L:
$C(mol/L) = \frac{n(moles)}{volume(L)}$
$ C(mol/L) = \frac{ 4.458\times 10^{- 3}}{ 1.5} $
$C(mol/L) = 2.972\times 10^{- 3}$
4. Analyzing the CaO's reaction with water, we got:
$1 CaO(aq) + H_2O(l) \ -- \gt Ca^{2+}(aq) + 2OH^-(aq)$
So, since CaO is a strong base that gives $2OH^-$ in its ionization reaction:
$[OH^-] = 2 * [CaO]= 2 * 2.972 \times 10^{-3} = 5.944 \times 10^{-3}M$
5. Calculate the pH:
$pOH = -log[OH^-]$
$pOH = -log( 5.944 \times 10^{- 3})$
$pOH = 2.226$
$pH + pOH = 14$
$pH + 2.226 = 14$
$pH = 11.774$
