Question

What is the molar mass of NaCl? If you need to add 0.2 moles of NaCl to 500 mL of water, how many grams of NaCl do you need to add?

Answer 1

321 g

Step-by-step explanation

All you need to know here is that the molarity of a solution tells you the number of moles of solute present in exactly

1 L

of the solution.

In your case, a

2.20-M

sodium chloride solution will contain

2.20

moles of sodium chloride, the solute, for every

1 L

of the solution.

So if every

1 L

of this solution must contain

2.20

moles of sodium chloride in order for the solution to have a molarity of

2.20 M

, it means that

2.50 L

of this solution must contain

2.50

L solution

⋅

2.20 moles NaCl

1

L solution

=

5.50 moles NaCl

To convert the number of moles of sodium chloride to grams, use the molar mass of the compound.

5.50

moles NaCl

⋅

58.4 g

1

mole NaCl

=

321 g

−−−−−

The answer is rounded to three sig figs.