Molarity Example Problem

A 4 g sugar cube (sucrose: C₁₂H₂₂O₁₁) is dissolved in a 350 ml teacup filled with hot water. What is the molarity of the sugar solution?

M = m/V
where M is molarity (mol/L)
m = number of moles of solute
V = volume of solvent (Liters)

Step 1 - Determine number of moles of sucrose in 4 g

C₁₂H₂₂O₁₁ = (12)(12) + (1)(22) + (16)(11)
C₁₂H₂₂O₁₁ = 144 + 22+ 176
C₁₂H₂₂O₁₁ = 342 g/mol
divide this amount into the size of the sample
4 g/(342 g/mol) = 0.0117 mol

Step 2 - Determine the volume of solvent in liters

350 ml x (1L/1000 ml) = 0.350 L

Step 3 - Determine the molarity of the solution

M = m/V
M = 0.0117 mol /0.350 L
M = 0.033 mol/L

Answer:

The molarity of the sugar solution is 0.033 mol/L.