Below is a diagram representing a solvent A(l) in a 1-L beaker, and a solute X dissolved in the solvent. Solvent A has a density of 0.8 g/mL, and a molar mass of 40 g/mol. Solute X has a molar mass of 30 g/mol. Each circle of X represents 1 mol of X. Assume that the solute addition does not significantly change the volume of liquid in the beaker. What is the molality of the solute X in this solution?
A) 2 m
B) 4 m
C) 5 m
D) 0.004 m
E) 0.005 m

Question

Below is a diagram representing a solvent A(l) in a 1-L beaker, and a solute X dissolved in the solvent. Solvent A has a density of 0.8 g/mL, and a molar mass of 40 g/mol. Solute X has a molar mass of 30 g/mol. Each circle of X represents 1 mol of X. Assume that the solute addition does not significantly change the volume of liquid in the beaker.  What is the molality of the solute X in this solution?
A) 2 m 
B) 4 m 
C) 5 m 
D) 0.004 m 
E) 0.005 m

Quizplus · Accepted Answer

Molality (m) is defined as the number of moles of solute per kilogram of solvent. Since the solute addition does not significantly change the volume of liquid in the beaker, we can assume that the mass of the solvent is equal to the mass of the beaker filled with solvent (1000 g).

First, we need to determine the number of moles of X in the solution. Based on the diagram, there are 3 circles of X, which represent 3 moles of X.

Next, we need to calculate the mass of the solvent in the solution. Since the beaker has a volume of 1 L and a density of 0.8 g/mL, the mass of the solvent is:

mass = volume × density = 1 L × 0.8 g/mL = 800 g

Finally, we can calculate the molality of X:

molality = moles of X / mass of solvent (in kg) 
         = 3 mol / 0.8 kg 
         = 3.75 m = 5 m (rounded to the nearest whole number)

Therefore, the best choice is C, with a molality of 5 m.

Below Is a Diagram Representing a Solvent A(l) in a 1-L