The density of a 56.0% by weight aqueous solution of methanol (CH3OH) is

0.9046 g/cm3. What is the molarity of the solution?

16.8

16.4

17.0

15.1

15.8

15.8 M CH3OH

Explanation:

Molarity is measured in Moles per liter of total solution.

Here, we are given 56% weight methanol and this means 44% solvent. We can use whatever ratio we would like but just calling it out of 100 g is the easiest. This means we have 56 g of methanol and 44 g of solvent. It says aqueous, so that means the solvent is water.

First, get the moles of the solute, methanol.

(56 g) * (1 mol / 32.042 g) = 1.75 mol methanol

Second, get the total volume using the given density and the grams we chose.

(100 g) / (0.9046 g / 1 mL) = 110.55 mL

Convert to liters

= 0.111 L

Third, use these values to find molarity.

1.75 mol / 0.111 L

= 15.8 M CH3OH