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10% solution of urea is isotonic with 6% solution of a non-volatile solute X.What is the molecular mass of solute X ?

A. 6 g mol⁻¹
B. 60 g mol⁻¹
C. 36 g mol⁻¹
D. 32 g mol⁻¹

User Remyremy
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1 Answer

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Final answer:

The molecular mass of a non-volatile solute X, which is isotonic with a 10% urea solution, is calculated using the proportionality between mass and moles of substances in isotonic solutions. By equalizing the moles of urea and X and knowing the mass of X is 6%, the molecular mass of X is determined to be 36 g/mol. Therefore, the correct option is C.

Step-by-step explanation:

The question asks for the molecular mass of a non-volatile solute X, given that a 10% urea solution is isotonic with a 6% solution of X. Isotonic solutions have the same osmotic pressure, which implies they have equal numbers of solute particles per unit volume. Knowing that urea (NH2)2CO has a molar mass of 60 g/mol, we can set up a proportion to find the molar mass of X, using the fact that the concentrations given are weight/volume percentages.

Considering a 100 mL solution for both solutes for simplicity, the mass of urea would be 10 g (10% of 100 mL), which corresponds to 10 g / 60 g/mol = 0.1667 mol. For the solute X in a similar 100 mL solution, the mass would be 6 g (6% of 100 mL). Since the solutions are isotonic, the number of moles of X must be the same as that of urea, 0.1667 mol. Thus, the molar mass of X can be calculated: Molar mass of X = Mass of X / Moles of X = 6 g / 0.1667 mol, which equals approximately 36 g/mol. Option C, 36 g/mol, is the correct answer.

User OlegWock
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