# Question 33dee

Aug 3, 2016

Here's what I got.

#### Explanation:

The key to this problem is the chemical formula for magnesium bromide, ${\text{MgBr}}_{2}$.

As you can see, one formula unit of magnesium bromide contains

• one magnesium cation, $1 \times {\text{Mg}}^{2 +}$
• two bromide anions, $2 \times {\text{Br}}^{-}$

This means that one mole of magnesium bromide, which contains $6.022 \cdot {10}^{23}$ formula units of this compound, will contain

• one mole of magnesium cations
• two moles of bromide anions

Now, you know that your sample contains $0.2$ moles of magnesium bromide. You can thus say that it contains

0.2 color(red)(cancel(color(black)("moles MgBr"_2))) * "1 mole Mg"^(2+)/(1color(red)(cancel(color(black)("mole MgBr"_2)))) = color(green)(|bar(ul(color(white)(a/a)color(black)("0.2 moles Mg"^(2+))color(white)(a/a)|)))

0.2 color(red)(cancel(color(black)("moles MgBr"_2))) * "2 moles Br"^(-)/(1color(red)(cancel(color(black)("mole MgBr"_2)))) = color(green)(|bar(ul(color(white)(a/a)color(black)("0.4 moles Br"^(-))color(white)(a/a)|)))#