Question #33dee

1 Answer
Stefan V.
Aug 3, 2016

Here's what I got.

Explanation:

The key to this problem is the chemical formula for magnesium bromide, "MgBr"_2MgBr2.

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

  • one magnesium cation, 1 xx "Mg"^(2+)1×Mg2+
  • two bromide anions, 2 xx "Br"^(-)2×Br−

This means that one mole of magnesium bromide, which contains 6.022 * 10^(23)6.022⋅1023 formula units of this compound, will contain

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

Now, you know that your sample contains 0.20.2 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)|)))

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