# How many grams of barium hydroxide required to dissolve in 156g of water to make a 0.247m solution?

Jul 2, 2016

6.60g of $B a {\left(O H\right)}_{2}$ is required.

#### Explanation:

To answer this question, we need two things:

• The molar mass of barium hydroxide, 171.34 g/mol
• The equation for molality:

We are given the molality and mass of solvent. The mass of solvent is expressed in terms of grams and we need kilograms so the following relationship must be used:

1000g = 1kg

Divide 156g by 1000 to obtain 0.156 kg of solvent.

Next, we determine the number of moles of solute (barium hydroxide), by rearranging the equation:

Moles of solute = Molality x Mass of solvent

Therefore, $0.247 m \times 0.156 k g$ = $0.0385 m o l B a {\left(O H\right)}_{2}$

Since we want the mass of $B a {\left(O H\right)}_{2}$, the number of moles of solute must be multiplied by the molar mass of the solute:

$0.0385 \cancel{m o l} \times \frac{171.34 g}{1 \cancel{m} o l}$

g $B a {\left(O H\right)}_{2}$ = 6.60g