Three students, A, B and C, are preparing sugar solutions for an experiment:

• Student A dissolves 20 g of sugar in 80 g of water.

• Student B dissolves 20 g of sugar in 100 g of water.

• Student C dissolves 30 g of sugar in 80 g of water.

(A) Calculate the mass percentage (% m/m) concentration of sugar in each student's solution.

(B) Whose solution is the most concentrated? Explain why.

(A) The mass by mass percentage is calculated by using the formula:

$$\text{Mass by mass \%} = \frac{\text{Mass of solute}}{\text{Mass of solution}} \times 100$$

Where, Mass of solution = Mass of solute + Mass of solvent

Student A: Mass of sugar = 20 g,

Mass of water = 80 g,

Mass of solution = 20 + 80 = 100 g

$$\% \text{ m/m} = \frac{20}{100} \times 100 = 20\% \text{ m/m}$$

Student B: Mass of sugar = 20 g,

Mass of water = 100 g,

Mass of solution = 20 + 100 = 120 g

$$\% \text{ m/m} = \frac{20}{120} \times 100 = 16.67\% \text{ m/m}$$

Student C: Mass of sugar = 30 g,

Mass of water = 80 g,

Mass of solution = 30 + 80 = 110 g

$$\% \text{ m/m} = \frac{30}{110} \times 100 = 27.27\% \text{ m/m}$$

(B) Student C's solution is the most concentrated, with a mass percentage of approximately 27.27% m/m. This is because the concentration of a solution depends on the amount of solute dissolved in a given mass of the solution, i.e., the higher the proportion of solute, the more concentrated the solution.