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Calorimetry Lab

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Joshua Mars

on 4 February 2013

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Transcript of Calorimetry Lab

By: Tara Mars, Courtney Golladay, Rachel Horn, Emily Davis- 7th Period Purpose Data and Observations Error Analysis Calorimetry Preparation Procedure To find the efficiency of the "homemade" calorimeter we used by determining the heat given off by two different substances, a cheese puff and a marshmallow. 1. Graduated Cylinder
2. Test tube Stand (with clamp)
3. Water
4. Thermometer
5. Small stand to hold food objects
6. Cheese Puffs
7. Marshmallows
8. Insulation (soda can)
9. Rag
10. Rubber Stoppers
11. Toothpicks
12. Test Tube Materials 1.Put 30 mL of water inside the test tube and attach the test tube to the stand. 2.Weigh the stand that the two marshmallows are placed on and then weigh the stand again with the two marshmallows to find the mass of the marshmallows. (It’s best to weigh the marshmallows with the stand rather than separately because later they will be massed with the stand—this is for consistency) 3.Place the thermometer inside the test tube without letting it touch the bottom of the tube. Note the temperature. 4.Place the stand with the marshmallow underneath the test tube and light the marshmallows with a match. 5.Immediately cover the marshmallow with the insulation (soda can) and rag over the top (around the test tube). 6.Place rubber stoppers underneath the can to allow for air flow, and thus allow oxygen to fuel the fire in order to burn the marshmallows completely. 7.Remove the insulation only once the temperature on the thermometer has stopped increasing. Note the temperature. 8.Record results and repeat steps one through seven with the cheese puff. By finding out the amount of energy that went into heating the water above the food substance being burned, we could calculate how much energy was released by the burning food substance. The calorimetry experiment’s purpose was to find out the efficiency of the calorimeter by determining the amount of heat that was produced by burning the substance.

The Calories per gram on the package for the cheese puff is 5.71. The efficiency for the calorimeter for the cheese puff came out to be 24.249%.

The Calories per gram on the package for the marshmallow is 3.3. The efficiency for the calorimeter for the marshmallows came out to be 10.216%. the science of measuring the amount of heat generated or consumed Major Errors Lack of even heating of the water because we didn’t stir the water before we took the final temperature. In A Perfect World... If we could repeat the experiment an infinite amount of times, that would decrease the amount of error that we have. Also, if none of the heat generated was lost to the surroundings, that would allow for greater accuracy. Finally, if we could have an actual calorimeter, that would make our results much more accurate. Effects of the Errors The lack of even heating could lead to a lower final temperature, and thus a smaller change in temperature, which would then cause the amount of energy release from the burning marshmallow/cheese puff to look as if it lost less than it actually did, affecting the efficiency percentage. It could also show a higher final temperature, also negatively affecting the efficiency percentage. Heat loss to the environment would also cause a lower final temperature and thus affect the percent efficiency. The heat loss could have been during the experiment, such as because of the cover/insulator we used, or because we unintentionally took time to place the marshmallows/ cheese puff under the test tube to heat the water. (This allowed some of the heat that burned the food to escape without heating the water, which would have affected the temperature.) Theoretically, we should have had about 4.02% efficiency, however, for the marshmallows we had 10.216% efficiency and for the cheese puffs we had 24.249% efficiency. The percent efficiency was much higher for the cheese puff because we did not completely burn it. Q = MCp T This was determined by finding out the amount of Calories per gram that were released by the burning (consumption) of the food substance. Q = MCp T The equation used in this experiment is: Used to determine the amount of energy absorbed or released. Data Analysis When we burned the food, the glucose molecules and the oxygen molecules combusted to form carbon dioxide, water, and most importantly, energy. The equation Q=MCp T helped us to determine the amount of energy that was given off by the burning food. This transformation from a complex molecule to a much simpler one released the stored chemical energy that was in the glucose. However, fire was required in this experiment because it takes energy to break bonds. This process also occurs in the body when we consume food. By calculating the energy that was put into the water to cause the temperature rise, we were able to convert to Calories from Joules (since 1 cal = 4.18 J and 1000 cal = 1 Cal) and divided by the amount of food substance burned to find out the Calories per gram of the substance. Marshmallows: (.337/ 3.3)X100= 10.216%.

Cheese puff: (1.385/ 5.71)X100= 24.249% (This percentage is high because the cheese puff was not burned all the way). We calculated the efficiency of the calorimeter to see how accurately the calorimeter can determine the actual calories there are in piece of food and whether we can use the data we obtained as accurate information. Once that was complete, we compared that to the Calories per gram on the nutrition label of the food substance by dividing and then multiplying by 100 to calculate the efficiency of the calorimeter. We used water, for which the specific heat is known, to calculate how much energy was released by the food substance via the absorption of energy into the water. The amount of energy absorbed by the water is therefore theoretically equal to the amount of energy that was given off by the food after it was burned. In real life, the efficiency of the calorimeter is important because if the efficiency is very low, then the data is not accurate and thus does not reflect the actual amount of calories in that particular food, which should not be distributed to the real world. Lighting the marshmallows much before we were able to place the cover on top. Using a soda can instead of something with more insulation (a lot of the heat escaped and didn’t heat up the water as much) Lighting the fire before we took the temperature of the water. Heat loss to the environment instead of heating the water.
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