Freezing Point Of Sugar And Salt Lab Report

695 Words2 Pages

Katrina Epps
Lab Partner: Jennifer Carter
Tim Little
CHE113-011
17 February 2014
Freezing Point of Sugar and Salt
Introduction
The purpose of this lab was to determine the molality of sugar and salt substance through calculating the freezing point depression (freezing point depression is the effect of lowering the freezing point of a substance due to an increased amount of solute added to the solvent in that the solute decreases the amount of vapor pressure) when the sugar or salt substance is added as a solute to a solvent with known properties. The results of the experiment confirmed our hypothesis that the freezing point would decrease more in the sugar than salt solvent. “The following mathematical expression that related freezing point depression and molality was developed: ΔTf=iKfm T is the change in temperature from the original freezing point, is the van’t Hoff factor, Kf is the freezing point depression constant for the solvent, and m is the molality of the solution. Molality is defined as the moles of solute per gram of solvent. Remember that we use molality instead of molarity because mass of solvent will not change with temperature.”(Lab Manual, 60)
Procedure
1. Put on goggles as you enter the lab
2. Get with lab partner
3. Set out test tube rack with 6 test tubes placed in the rack
4. Need small and large graduated cylinder. These will be used to measure distilled water.
5. Need 200ml beaker and 25 ml beaker
6. Lab partner 1 should get sugar in weigh boat and weigh it (4x). Lab partner 2 set up measurenet.
7. Calibrate temp probe before starting trials.
8. While lab partner 1 is still working with the sugar, lab partner 2 need to get salt in weigh boat and weigh it (record in notebook) and also need to get some disti...

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...11 and 2.47613) was much lower than the salt temperature solution (38).
Conclusion
This lab was done to provide another way of determining the molality and concentration of a sugar and salt solution. The method to provide this information was through the use of colligative properties, and more specifically, freezing point depression. When a solute is added to a solvent, the point at which the solution freezes is lower than the freezing point of the pure solvent alone. This change in temperature is equal to the freezing point depression constant multiplied by the van’t Hoff factor of the solute and the molality of the solution. Because molality is equal to moles of solute divided solvent, the moles of solute can be experimentally obtained by finding the change in temperature and knowing the freezing point depression constant, van’t Hoff factor, and solvent used.

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