Chemistry Practice Problems Molality Practice Problems Solution: The density of acetonitrile (CH3 CN) is 0.786 g/mL...

Solution: The density of acetonitrile (CH3 CN) is 0.786 g/mL, and the density of methanol (CH3 OH) is 0.791 g/mL. A solution is made by dissolving 23.0 mL CH3 OH in 98.7 mL CH3 CN.What is the molality of the solution? Assuming CH3OH is the solute and CH3CN is the solvent.

Problem

The density of acetonitrile (CH3 CN) is 0.786 g/mL, and the density of methanol (CH3 OH) is 0.791 g/mL. A solution is made by dissolving 23.0 mL CH3 OH in 98.7 mL CH3 CN.

What is the molality of the solution? Assuming CH3OH is the solute and CH3CN is the solvent.

Solution

In this problem, we are being asked to calculate for the molality of the solution prepared by dissolving 23.0 mL of CH3OH in 98.7 mL of CH3CN.

 

 When calculating for molality, we use the following equation:

Molality(m)=mol solutekg solvent


We will calculate the molality of the solution using the following steps:

Step 1: Calculate the moles of solute.
Step 2: Calculate the mass of the solvent (in kg).
Step 3: Calculate the molality of the solution.


CH3OH → dissolved in CH3CN → Solute

CH3CN → where CH3OH is dissolved → Solvent


Step 1: Calculate the moles of CH3OH.

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