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"_2#.

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

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

This means that one mole of magnesium bromide, which contains #6.022 * 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)|)))#

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