We’re being asked to **determine the moles of CO(NH _{2})_{2}** present in

Recall that the freezing point of a solution is *lower* than that of the pure solvent and the ** change in freezing point (ΔT_{f})** is given by:

$\overline{){{\mathbf{\Delta T}}}_{{\mathbf{f}}}{\mathbf{=}}{{\mathbf{T}}}_{\mathbf{f}\mathbf{,}\mathbf{}\mathbf{pure}\mathbf{}\mathbf{solvent}}{\mathbf{-}}{{\mathbf{T}}}_{\mathbf{f}\mathbf{,}\mathbf{}\mathbf{solution}}}$

The ** change in freezing point** is also related to the molality of the solution:

$\overline{){{\mathbf{\Delta T}}}_{{\mathbf{f}}}{\mathbf{=}}{{\mathbf{imK}}}_{{\mathbf{f}}}}$

where:

**i** = van’t Hoff factor

**m** = molality of the solution (in m or mol/kg)

**K _{f}** = freezing point depression constant (in ˚C/m)

Recall that the ** molality of a solution** is given by:

$\overline{){\mathbf{molality}}{\mathbf{=}}\frac{\mathbf{moles}\mathbf{}\mathbf{solute}}{\mathbf{kg}\mathbf{}\mathbf{solvent}}}$

**For this problem, we need to do the following:**

**Step 1:**** **Calculate for ΔT_{f}.

* Step 2:* Determine the molality of the solution.

* Step 3:* Calculate the mass of CO(NH

How many moles of CO(NH _{2})_{2} are present in 131 g of water, if the freezing point of the solution is −4.02 °C? k_{f} (water) =1.86 C • kg/mol.

1. 0.263 mol

2. None of these

3. 0.280 mol

4. 0.297 mol

5. 0.288 mol

6. 0.272 mol

Frequently Asked Questions

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Freezing Point Depression concept. If you need more Freezing Point Depression practice, you can also practice Freezing Point Depression practice problems.

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Our tutors rated the difficulty of*How many moles of CO(NH 2)2 are present in 131 g of water, i...*as medium difficulty.

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