Five per cent solution of a solute (X) is isotonic with 0.855% solution of sucrose (molecular weight — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

Isotonic solutions have equal concentrations: C_X = C_sucrose. For a 5% (w/v) solution, there are 5 g of solute in 100 mL of solution: C_X = (5 / M_X) * (1000 / 100) = 50 / M_X. For 0.855% (w/v) sucrose solution: C_sucrose = (0.855 / 342) * (1000 / 100) = 8.55 / 342 = 0.025 M. Equating the two concentrations: 50 / M_X = 0.025 => M_X = 50 / 0.025 = 2000 g/mol.