Question

How many moles of glucose would be needed to lower the freezing point of one kg of water 3.72°C?

Answer 1

• 2 moles of glucose would be needed to lower the freezing point of one kg of water 3.72ºC.

Step-by-step explanation:

Lowering the freezing point of a solvent, when a nonvolatils solute is added, is a colligative property that follows the equation:

`\Delta T_f=m* k_f* i`

Where:

• ΔTf is the depression on the freezing point
• Kf is the molal kryoscopic constant of the solvent. For water it is 1.86 ºC/m
• i is the van't Hoff factor. For molecular compounds, such as glucose, it is 1.

Then, you can calculate the molality of the solution:

• 3.72ºC = m × 1.86ºC/m × 1

Clear m:

• m = 3.72ºC / (1.86ºC/m)

• m = 2 mol of solute /kg of solvent

Since molality is the number of moles per kg of solvent, you would need 2 moles of glucose to lower the freezing point of one kg of water 3.72ºC.