Answer:
20 g H₂O
Explanation:
We are given the following information about a solution:
- its molarity is 2.5 M (moles per liter)
- the solute's mass is 8.2 g
We can solve for the mass of water using stoichiometry, or unit conversion. We need to know the following values:
- molar mass of calcium nitrate:
\(M_{\rm Ca(NO_3)_2} = [40.08 + 2(14.01 + 3(16.00))]\ g\text{/mol} = 164.10\ g/\text{mol}\) - density of water:
\(\rho_{\rm H_2O} = \dfrac{1000\ g}{1\text{ L}}\)
↓↓↓
\(\rm \dfrac{8.2g}{1}\times\dfrac{1\ mol\ Ca(NO_3)_2}{164.10\ g\ Ca(NO_3)_2} \times \dfrac{1\ L\ H_2O}{2.5\ mol\ Ca(NO_3)_2} \times \dfrac{1000\ g \ H_2O}{1\ L\ H_2O} = \boxed{\rm20\ g\ H_2O}\)
