Question

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

Answer 1

6.60g of `Ba(OH)_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 xx 0.156kg` = `0.0385 mol Ba(OH)_2`

Since we want the mass of `Ba(OH)_2`, the number of moles of solute must be multiplied by the molar mass of the solute:

`0.0385 cancel(mol)xx(171.34g)/(1cancelmol)`

g `Ba(OH)_2` = 6.60g