Instructions To complete a table entry titled ” Measured “, copy your measurement that you made in the previous week.

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Instructions

To complete a table entry titled “Measured”, copy your measurement that you made in the previous week. If you

ran the experiment again to obtain the different measurement, then check the box above the table so that your Coach

will know why the numbers are different from ones reported in the Prelab and Data. Although there will be no

points for completing a table entry, one point will be deducted if the data is missing or for the incorrect use of

significant figures and units. So make sure to write them down correctly.

Part A: Preparing Solutions

Solution B

I redid the experiment.

Measured Mass of NaCl Measured Volume of Water

1. Answer each question with correct significant figures and units. You must show calculations for determining

each quantity. If necessary, use the molar mass of NaCl = 58.44 g/mol.

a. Determine the number of moles of NaCl in the solution. (5 points)

b. Determine the number of moles of all solutes (both cations and anions) from the number of moles of NaCl that

you determined above. For this question, in addition to your calculation, explain the idea behind your calculation. (5

points)

c. Determine the mass (in kg) of solvent (assume that the density of water is 1.000 g/mL). (5 points)

d. Determine the molality (in m or mol/kg) of all solutes. (5 points)

CHEM 1451 Lab Week 09 Colligative Properties Postlab Report

2

Name: Date:

Coach’s Name

Solution C

I redid the experiment.

Measured Mass of NaCl Measured Volume of Water

2. Answer each question with correct significant figures and units. You must show calculations for determining

each quantity. If necessary, use the molar mass of NaCl = 58.44 g/mol.

a. Determine the number of moles of NaCl in the solution. (5 points)

b. Determine the number of moles of all solutes (both cations and anions) from the number of moles of NaCl that

you determined above. For this question, in addition to your calculation, explain the idea behind your calculation. (5

points)

c. Determine the mass (in kg) of solvent (assume that the density of water is 1.000 g/mL). (5 points)

d. Determine the molality (in m or mol/kg) of all solutes. (5 points)

CHEM 1451 Lab Week 09 Colligative Properties Postlab Report

3

Name: Date:

Coach’s Name

Solution D

I redid the experiment.

Measured Mass of NaCl Measured Volume of Water

3. Answer each question with correct significant figures and units. You must show calculations for determining

each quantity. If necessary, use the molar mass of NaCl = 58.44 g/mol.

a. Determine the number of moles of NaCl in the solution. (5 points)

b. Determine the number of moles of all solutes (both cations and anions) from the number of moles of NaCl that

you determined above. For this question, in addition to your calculation, explain the idea behind your calculation. (5

points)

c. Determine the mass (in kg) of solvent (assume that the density of water is 1.000 g/mL). (5 points)

d. Determine the molality (in m or mol/kg) of all solutes. (5 points)

CHEM 1451 Lab Week 09 Colligative Properties Postlab Report

4

Name: Date:

Coach’s Name

Part C: Measuring the Freezing Point of Water

I redid the experiment.

Measure Freezing Point of Water

Part D: Measuring the Freezing Point of NaCl Solutions

I redid the experiment.

Measured

Freezing Point of

Solution B

Measured

Freezing Point of

Solution C

Measured

Freezing Point of

Solution D

4. Using the measured freezing point of distilled water in Part C, calculate the freezing point depression ΔT for

NaCl solutions from Part D. The freezing point depression ΔT is calculated by the following formula.

ΔT = (Measured freezing point of water in Part C) − (Measured freezing point in Part D)

a. Determine the freezing point depression ΔT for Solution B. Show your calculation. (5 points)

b. Determine the freezing point depression ΔT for Solution C. Show your calculation. (5 points)

c. Determine the freezing point depression ΔT for Solution D. Show your calculation. (5 points)

CHEM 1451 Lab Week 09 Colligative Properties Postlab Report

5

Name: Date:

Coach’s Name

5. Determine the molal freezing point depression constant (Kf) (in °C⋅kg/mol) of water by using the data of three

NaCl solutions. Use Equation 3 in the “Background and Procedure” file, the molality values of all solutes from

Questions 1 – 3 and the freezing point depression (ΔT) from Question 4. In your calculation, rewrite the symbol

“m” (the molality) as “mol/kg” so that the molal freezing point depression constant will have the correct unit.

Make sure to show all your work to receive credits.

a. Use the data of Solution B and determine the molal freezing point depression constant (Kf) (in °C⋅kg/mol) of

water. (5 points)

b. Use the data of Solution C and determine the molal freezing point depression constant (Kf) (in °C⋅kg/mol) of

water. (5 points)

c. Use the data of Solution D and determine the molal freezing point depression constant (Kf) (in °C⋅kg/mol) of

water. (5 points)

CHEM 1451 Lab Week 09 Colligative Properties Postlab Report

6

Name: Date:

Coach’s Name

6. Analysis of Results

a. Determine the average value of three molal freezing point depression constant (Kf) values of water from Question

5 (in °C⋅kg/mol). (5 points)

b. The published value for Kf of water is 1.86°C∙kg/mol (use this as the true value). Determine the % error of the

average value of the molal freezing point depression constant that you found in Question 6 a.

average value true value

%error 100%

true value

= ×

The % error is an example of the mixed operation. In order to receive the full credits, make sure to show each step

of calculations. In other words, show the result of the calculation in the numerator explicitly before dividing the

numbers. (5 points)

 
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