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

use the molar mass of magnesium chloride to determine how many moles you would have in that sample

use the solution's molarity to find how many liters would contain that many moles

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")#