A $0.9%$ (w/v) $NaCl$ solution ( $9.0 g$ per litre; molar masses $NaCl = 58.5$ , glucose $= 180 g mo l^{- 1}$ ) is isotonic with a glucose solution at the same temperature. Assuming $NaCl$ is completely dissociated, find the mass of glucose per litre of the glucose solution, in grams (nearest integer).

Numerical answer type, answer in g, tolerance 1.

Answer: 55 g

Isotonic solutions have equal total particle concentration.

NaCl

(9.0/58.5) \times 2 = 0.3077 mol L^{- 1}

of particles. Glucose needs the same concentration, so mass

= 0.3077 \times 180 = 55.38 g L^{- 1}

, i.e. about 55 g.