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Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
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Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

Solution: 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? kf (water) =1.86 C • kg/mol.1. 0.263 mol2. None of these3. 0.280 mol4. 0.297 mol5. 0.288 m

Solution: 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? kf (water) =1.86 C • kg/mol.1. 0.263 mol2. None of these3. 0.280 mol4. 0.297 mol5. 0.288 m

Problem

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? kf (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

Solution

We’re being asked to determine the moles of CO(NH2)2 present in 131 g water to get a solution with a freezing point of –4.02 ˚C.


Recall that the freezing point of a solution is lower than that of the pure solvent and the change in freezing point (ΔT­f) is given by:


ΔTf=Tf, pure solvent-Tf, solution


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


ΔTf=imKf


where: 

i = van’t Hoff factor

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

Kf = freezing point depression constant (in ˚C/m)


Recall that the molality of a solution is given by:


molality=moles solutekg solvent


For this problem, we need to do the following:

Step 1: Calculate for ΔTf.

Step 2: Determine the molality of the solution.

Step 3: Calculate the mass of CO(NH2)2 present.


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