Question

Pre-Lab Questions: Freezing Point Depression

Name ________________ Lab Section __________

Read the description of the experiment. Make sure you understand it before you go any further.

1. Graph the following data (use graph paper and a ruler). You can get graph paper from the lab, or print it from a web site. Draw best-fit lines (really best fit curves).They will be similar in shape to these shown on the graph in the "Background" section. Use different colors to draw data points and curves for water and NaCl solution. Apply explanation provided for the figure in  "Background" section, to determine the freezing point depression of the NaCl solution.

Water

Time (s)                  Temp °C

30                                13.4

60                                5.9

90                                -0.7

120                              0.4

150                              0.4

180                              0.5

210                              0.3

240                              0.3

270                              0.4

300                              0.4

330                              0.2

360                              -0.1

NaCl solution

Time (s)                 Temp °C

30                                13.2

60                                4.6

90                                -4.1

120                              -6.2

150                              -3.0

180                              -3.3

210                              -3.6

240                              0.3

270                              0.4

300                              0.4

330                              0.2

360                              -0.1

Freezing point Water: ______ Freezing point NaCl solution _______Freezing point depression (Δt): _____

2. What is the freezing point depression (DT) of water in a solution of 17.1 g of sucrose, C₁₂H₂₂O₁₁, in 200.0 g of water? What is the actual freezing point of the solution in ⁰C?

Calculations:

Freezing point of the solution     =  ______⁰C            Freezing point depression (DT) = _____________

                                                                                                                                                         next page→

3. What is the freezing point of 1 m acetic acid (note: it is not pure acetic acid, but a water solution of the acetic acid). What, if any, assumptions do you need to make? _________________________________________

4. What is the expected freezing point depression for a solution that contains 2.0 moles of sodium sulfate dissolved in 1.0 kg of water?

5. The freezing point of an aqueous sodium chloride solution is –0.20 ^oC. What is the molality of the solution?

6.  Mercury (I) nitrate should have the formula HgNO₃, but spectroscopic and freezing point depression studies indicate (and it is now accepted) that in fact the formula is Hg₂(NO₃)₂ (because the mercury(I) ion is a diatomic ion Hg₂^2+.).  What value for i would you expect for a 1 m solution based on the formula HgNO₃? What would be the ivalue for Hg₂(NO₃)₂?

HgNO₃                 i = ___

Hg₂(NO₃)₂       i = ___

7. Using salt as a de-icing substance can result in corrosion problems. Search chemical literature or other available sources to find out what other chemicals can (and are) used instead.  Do they have any disadvantages?

8. What mass of NaCl you need to prepare 10 g of  1m NaCl                       

Calculations:

9. How would you prepare 10 g of 1 m Al (NO₃)₃ using Al (NO₃)₃ * 9 H₂O as your solute.

Calculations:

                                                I would dissolve  ________ g of Al (NO₃)₃ * 9 H₂O    in ______ g water

What, if any, assumption(s) have you made? _________________________________________

Answer 1