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 is defined as moles of solute per kilogram of solvent. Since the volume of the solution is not significantly changed, we can assume that the mass of the solvent is still 1 kg. Therefore, we need to determine the number of moles of solute in the solution. 
From the diagram, we can see that there are 4 circles of X, which represents 4 moles of X. 
Molality = moles of solute / mass of solvent in kg 
Moles of solute = 4 
Mass of solvent = volume of solvent x density = 1 L x 0.8 g/mL = 800 g = 0.8 kg 
Molality = 4 moles / 0.8 kg = 5 m

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