Question

The term "proof" is defined as twice the percent by volume of pure ethanol in solution. thus, a solution that is 95% (by volume) ethanol is 190 proof. what is the molarity of ethanol in a 92 proof ethanol/water solution? density of ethanol = 0.80 g/cm³ density of water = 1.0 g/cm³ mol. wt. of ethanol = 46 g/mol

a) 0.46 m
b) 0.80 m
c) 0.92 m
d) 8.0 m
e) 17 m

Answer 1

The molarity of a 92 proof ethanol/water solution is calculated by determining the volume of ethanol based on its proof, converting that to mass using ethanol's density, then finding the moles using the molar weight, and finally calculating molarity. The molarity in this case is found to be 8.0 M.

Step-by-step explanation:

To calculate the molarity of ethanol in a 92 proof ethanol/water solution, we first need to understand that proof represents twice the percent by volume. Hence, 92 proof is 46% ethanol by volume. To find the molarity, we need to calculate the number of moles of ethanol and then divide it by the volume of the solution in liters.

Assuming we have 100 mL of solution:

1. Calculate the volume of ethanol: 46 mL (since it's 46% of the solution).
2. Find the mass of ethanol using its density (0.80 g/cm³): mass = density × volume = 0.80 g/cm³ × 46 cm³ = 36.8 g.
3. Convert the mass of ethanol to moles: 36.8 g ÷ 46 g/mol = 0.80 moles.
4. Convert 100 mL solution to liters: 100 mL × 0.001 L/mL = 0.1 L.
5. Finally, divide the moles of ethanol by the volume of the solution to get molarity: 0.80 moles ÷ 0.1 L = 8.0 M.