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# Percent Composition by Mass

## Worked Chemistry Problems

By Todd Helmenstine

Sugar cubes are pre-measured blocks of sucrose.

Uwe Hermann
Question:

A 4 g sugar cube (Sucrose: C12H22O11) is dissolved in a 350 ml teacup of 80 °C water. What is the percent composition by mass of the sugar solution?
Given: Density of water at 80 °C = 0.975 g/ml

Definition

Percent Composition by Mass is the mass of the solute divided by the mass of the solution (mass of the solute plus mass of the solvent), multiplied by 100.

Step 1 - Determine mass of solute

We were given the mass of the solute in the problem. The solute is the sugar cube.
masssolute = 4 g of C12H22O11

Step 2 - Determine mass of solvent

The solvent is the 80 °C water. Use the density of the water to find the mass.
density = mass/volume
mass = density x volume
mass = 0.975 g/ml x 350 ml
masssolvent = 341.25 g

Step 3 - Determine the total mass of the solution

msolution = msolute + msolvent
msolution = 4 g + 341.25 g
msolution = 345.25 g

Step 4 - Determine percent composition by mass of the sugar solution.

percent composition = (msolute / msolution) x 100
percent composition = ( 4 g / 345.25 g) x 100
percent composition = ( 0.0116 ) x 100
percent compostion = 1.16%

The percent composition by mass of the sugar solution is 1.16%