How many milliliters of a 2.5 M #MgCl_2# solution contain 17.5 g #MgCl_2#?
1 Answer
Explanation:
Your strategy here will be to
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use the molar mass of magnesium chloride to determine how many moles you would have in that sample
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use the solution's molarity to find how many liters would contain that many moles
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convert the volume from liters to milliliters
So, magnesium chloride,
You are interested in finding out what volume of your
This mass of magnesium chloride will be equivalent to
#17.5 color(red)(cancel(color(black)("g"))) * "1 mole MgCl"_2/(95.211 color(red)(cancel(color(black)("g")))) = "0.1838 moles MgCl"_2#
Now, molarity is defined as moles of solute, which in your case is magnesium chloride, divided by liters of solution
#color(blue)("molarity" = "moles of solute"/"liters of solution")#
This means that the volume of your solution that contains
#color(blue)(c = n/V implies V = n/c)#
#V = (0.1838 color(red)(cancel(color(black)("moles"))))/(2.5color(red)(cancel(color(black)("moles")))/"L") = "0.07352 L"#
Finally, convert this value to milliliters by using the conversion factor
#"1 L" = 10^3"mL"#
This will get you
#0.07352color(red)(cancel(color(black)("L"))) * (10^3"mL")/(1color(red)(cancel(color(black)("L")))) = "73.52 mL"#
Rounded to two sig figs, the number of sig figs you have for the molarity of the solution, the answer will be
#V = color(green)("74 mL")#