# A solution contains 0.600 g of #Mg^(2+)# in enough water to make a 1930 mL solution. What is the concentration in milliequivalents per liter (mEq/L)?

##### 1 Answer

#### Explanation:

Your strategy here will be use determine how many moles of magnesium your solution will contain by using magnesium's *molar mass*.

Once you know the number of moles of magnesium cations, you can determine how many **equivalents** you have.

So, magnesium has a molar mass of **one mole** of magnesium cations will have a mass of

In your case, the solution will contain

#0.600 color(red)(cancel(color(black)("g Mg"^(2+)))) * "1 mole Mg"^(2+)/(24.3050color(red)(cancel(color(black)("g Mg"^(2+))))) = "0.02469 moles Mg"^(2+)#

For an ion in aqueous solution, the number of **equivalents** will be equal to the number of moles of that ion multiplied by its *valence*.

#color(blue)("Eq" = "moles" xx "valence")#

As you know, magnesium has a valence of

#"0.02469 moles Mg"^(2+) xx 2 = "0.04938 Eq Mg"^(2+)#

To express this value in *milliequivalents*,

#"1 Eq" = 10^3"mEq"#

This will get you

#0.04938 color(red)(cancel(color(black)("Eq"))) * (10^3"mEq")/(1color(red)(cancel(color(black)("Eq")))) = "49.38 mEq"#

Finally, to get the magnesium cations' concentration in *milliequivalents per liter*, divide the number of mEq by the volume of the solution - **do not** forget to convert it to *liters*!

#["Mg"^(2+)] = "49.38 mEq"/(1930 * 10^(-3)"L") = color(green)("25.6 mEq/L")#