Question

What is the molarlity of a D-mannose solution prepared by dissolving 45.0 g of D-mannose, C6H12O6, in 125.9 g of water?

a) 1.98×10−3 m

b) 9.81×10−3 m

c) 1.46 m

d) 0.358 m

e) 1.98 m

Answer 1

Molar mass of D-mannose (C₆H₁₂O₆) = 12*6 + 1*12 + 16*6 = 180

Given mass of D-mannose = 45.0g

Moles = Given/Molar mass

Moles of D-mannose = 45/180 = 0.25

Given mass of water = 125.9g or 0.1259kg (1kg = 1000g)

Molality = Moles of solute/Mass of solvent in kg

Solute is D-mannose and solvent is water.

Molality of solution = 0.25/0.1259

= 1.98m

So option (e) is correct.

Note - In the question molarity should be edited with molality as options are given for molality.