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.
We used the pipette filler and filled the glucose rinsed pipette to add 10ml of 10% of glucose in test tube 0.
In addition, the water is mixed with salt, which allows the cold pack to stay cool. The mixture that occurs between the salt and the water causes an endothermic reaction, which means that heat is absorbed. Due to the heat absorption, the temperature of the solution will decrease substantially. The cold pack experiment lab allowed us, the students, to apply theories learned in class to actual real life experiments; such experiments prepare us for future tasks the will be put forth to determine. Our main trajectory through this assignment was to determine what our unknown salt was, through experimental analysis.
We’d note down the weight. Then we’d get our solutions ready. We were only given a 100% solution and a 0% solution, so we had to mix them in the right ratio to get all the solutions we needed. We decided to do 5 different types of solutions so we would have a wide range of results and it would be more accurate. We’d use 100%, 75%, 50%, 25%, 0% solutions in our experiment.
To investigate the osmotic effect of changing the concentration of sucrose solution; distilled water, 20% sucrose solution, 40% sucrose solution, 60% sucrose solution on the change in mass of potato cylinder after 30 minutes of being in solution.
For this experiment, you will add the measured amount of the first sample to the measured amount of the second sample into its respectively labeled test tube then observe if a reaction occurs. In your Data Table, record the samples added to each test tube, describe the reaction observed, if any, and whether or not a chemical reaction took place.
The mixture was poured through a weight filter paper and Sucrose washed with a 5ml of dichloromethane. The resulting solid was left in a breaker to dry for one week, to be measured. Left it in the drawer to dry out for a week and weighted it to find the sucrose amount recovered amount.
3.) Divide your 30g of white substance into the 4 test tubes evenly. You should put 7.5g into each test tube along with the water.
The temperature probe was placed into the test tube and recorded the temperature of the freezing solution using Logger Pro software. The test tube was held against the inner glass of the ice bath beaker so the test tube was visible to see when the solution froze over. Once the freezing point was measured, the temperature stopped being monitored and the data was recorded. The steps mentioned above for finding the freezing point, also known as ΔTf, was replicated for the 0.0, 0.4, and 0.6 concentrations. To find the freezing point depression, the equation ΔTf = imKf was used. The molality (m) of each solution was then calculated dividing moles of solute by kilograms of solvent, and the Kf value for magnesium chloride is known to be -1.86. Since magnesium chloride breaks down into three ions in deionized water, it was concluded that the Van’t Hoff factor couldn’t exceed three. For better accuracy, the experiment explained above for finding the freezing point depression and Van’t Hoff factor was re-conducted exactly the same to determine more accurate results. Again, the molality of each solution was calculated, and a graph expressing the change in freezing temperature verses molality
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* Amount of sugar solution in each test tube. * The potatoes have to have the same mass.
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First, the mass of the beaker being used was recorded, then about 1g of baking soda was added and the mass recorded. Next, the mass of just the baking soda was found and recorded. Then, the contents were boiled until dry then weighed and mass recorded after cooling off. Finally, the mass of jus the salt, or sodium chloride, was found and recorded.
Weigh out two 0.100 g. samples of the product and put each into a test
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