Calculate the molarity of a solution which is prepared by dissolving 28.4 g of 3 NaCl in
400 cm^3 of solution.
Answers
Answer:
In order to find the molarity of the solution, you must determine the number of moles of solute present in exactly
1 L
=
10
3
mL
of solution. Notice that you already know the number of milligrams of sodium chloride, the solute, present in
4 mL
of solution, so start by calculating the mass of solute present in
10
3
mL
of solution.
10
3
mL solution
⋅
240 mg NaCl
4
mL solution
=
60
⋅
10
3
mg
Since
1 g
=
10
3
.
mg
you can say that
10
3
mL
of solution contain
60
⋅
10
3
.
mg
=
60
.
g
of sodium chloride. Now, to convert this to moles, use the molar mass of the compound
60
g
⋅
1 mole NaCl
58.44
g
=
1.027 moles NaCl
Since this represents the number of moles of sodium chloride present in
10
3
mL
of solution, you can say that the molarity of the solution is equal to
molarity = 1 mol L
−
1
−−−−−−−−−−−−−−−−−−−
The answer must be rounded to one significant figure, the number of sig figs you have for the volume of the solution.