# Question 07b8f

Feb 17, 2017

${\text{0.75 moles BaCl}}_{2}$

#### Explanation:

A solution's molality is simply a measure of how many moles of solute you get for every $\text{1 kg}$ of solvent.

In your case, a $\text{3.0 m}$ barium chloride solution will contain $3.0$ moles of barium chloride, your solute, for every $\text{1 kg}$ of water, your solvent.

You can thus use the molality of the solution as a conversion factor to help you figure out how many moles of solute you need to have in

250 color(red)(cancel(color(black)("g"))) * "1 kg"/(10^3color(red)(cancel(color(black)("g")))) = "0.250 kg"#

of water in order to have a $\text{3.0 m}$ solution. You can thus say that you need

$0.250 \textcolor{red}{\cancel{\textcolor{b l a c k}{{\text{kg water"))) * overbrace("3.0 moles BaCl"_2/(1color(red)(cancel(color(black)("kg water")))))^(color(blue)("= 3.0 m")) = color(darkgreen)(ul(color(black)("0.75 moles BaCl}}_{2}}}}$

The answer is rounded to two sig figs.