Question

The percent by mass of methanol (MM = 32.04 g/mol) in an aqueous solution is 21.1%. What is the molality of the methanol solution?

Answer 1

To find the molality of methanol in a 21.1% solution, calculate the moles of methanol using its molar mass, find the mass of water in kilograms, and divide the moles of methanol by the kilograms of water. The molality is 8.34 mol/kg.

Step-by-step explanation:

To calculate the molality of methanol in an aqueous solution with a mass percentage of 21.1%, we follow these steps:

1. Calculate the mass of methanol in 100 g of the solution. 21.1 g of methanol, because 21.1% of 100 g is 21.1 g.
2. Calculate the mass of water in the solution by subtracting the mass of methanol from the total mass of the solution (100 g - 21.1 g = 78.9 g of water).
3. Convert the mass of water to kilograms (78.9 g = 0.0789 kg).
4. Use the molar mass of methanol (32.04 g/mol) to convert the mass of methanol to moles (21.1 g / 32.04 g/mol).
5. Divide the number of moles of methanol by the kilograms of water to find the molality.

Using the molar mass of methanol (32.04 g/mol), we have:

• Mass of methanol = 21.1 g
• Number of moles of methanol = 21.1 g / 32.04 g/mol = 0.658 moles
• Mass of water = 78.9 g = 0.0789 kg
• Molality = 0.658 moles / 0.0789 kg = 8.34 mol/kg (which is the molality of methanol in the solution).

Answer 2

Molality of the methanol solution = 8.33 m

Step-by-step explanation:

Given:

Mass % = 21.1 %

Molar mass of methanol = 32.04 g / mol

Find:

Molality of the methanol solution?

Computation:

Moles of methanol = Mass / Molar mass

Moles of methanol = = 21.1 / 32.04

Moles of methanol = 0.658

Assume.

Mass of solution = 100 g

Mass of solvent = 100 -21.1 = 78.9 g = 0.0789 kg

Molality of the methanol solution = 0.658 / 0.0789

Molality of the methanol solution = 8.33 m