Calculate the molarity.

Question

The solution contains 21.7g of NaCl in a 653 mL solution.

Answer 1

The NaCl solution is 21.7g / 653ml

or 33.231g / 1L (divide 21.7g by 0.653 liter)

A 1 molar solution of NaCl is 58.44g / 1L (This is based on the molecular weight of NaCl)

To figure out what the molarity of the solution in question is you want to know the ratio between the unknown solution and the 1molar solution.

58.44*X = 33.231 . . .

X = 33.231/58.44

X = 0.568

or 568mM (millimolar)

Once you know that the unknown solution is 33.231g / 1L you get a ballpark idea of what the molarity is when you compare to the 1molar solution of 58.44g / 1L. Just by looking at the numbers you can see it's a little more than half as much NaCl so you know the answer should be in the 0.5M to 0.6M range.

Answer 2

Molar mass NaCl = 58.4 g/mol

molarity = moles NaCl / liter of solution

moles NaCl = 21.7 g NaCl x 1 mol NaCl / 58.4 g = 0.372 moles NaCl

liters of solution = 653 mls x 1 L / 1000 mls = 0.653 L

Molarity = 0.372 mols / 0.653 L = 0.570 M (3 sig. figs.)