If I leave 750 mL of a 0.40 M sodium chloride solution uncovered on a windowsill
and 150 mL of the solvent evaporates, what will the new concentration of the
sodium chloride solution be?
A. 0.2 molar
B. 0.5 molar
C. 1.0 molar
D. 1.2 molar

B. 0.5 molar

Explanation:

Given data:

Initial concentration = 0.40 M

Initial volume = 750 mL

Final volume =750  -  150 mL = 600 mL

Final concentration = ?

Solution:

Molarity is the number of moles of solutes in litter of solvent. In given problem it is stated that when the solution is uncovered solvent evaporate it means molarity is changed. we can calculate the new molarity with the following formula.

C₁V₁ = C₂V₂

C₁ = initial concentration

V₁ = initial volume

C₂ = final concentration

V₂ = final volume

Now we will put the values in formula.

C₁V₁ = C₂V₂

0.40 M × 750 mL = C₂ × 600 mL

300 M.mL / 600 mL = C₂

0.5 M = C₂