Oh Nuts! – Calories Count

 
Energy comes in a variety of forms: light, heat, motion, electricity, and so forth.  The energy stored in food is measured in units of Calories.  A Calorie is defined as the quantity of heat it takes to raise the temperature of 1 kg of water 1°C.  (Don’t confuse Calories with calories: 1Calorie = 1000 calories – Tricky!)  The energy in food is seen as heat because the energy is released as heat when food is combusted (or burned).  Complete combustion results in the production of energy, carbon dioxide and water.  Look for evidence of these products during the lab. 

In this lab, you will measure the amount of energy in calories in two types of nuts: peanuts and almonds.  The accepted values for these nuts are 5180 calories/gram for peanuts and 5470 calories/gram for almonds.  When you eat nuts, the energy in the nuts is converted to a useful form, giving your body the energy it needs. 

Precautions

Throughout this lab, we will have open flames in the lab.  Make sure that your hair and any loose clothing that you are wearing do not come into contact with the flames.  Wear your safety goggles at all times during the lab.  Make sure that all flames are extinguished properly when you are finished and are completely cool before you place them in the trash. 

Procedure

1. Measure the mass (in grams) of a nut.  Record data in chart. 

2. CAREFULLY place the nut on the tip of the needle (you don’t need to push it on very far). 

3. Measure the mass of an EMPTY soda can.  Add water to the can until it is half full.  Take the mass again.  Record the two masses in the data chart.  You can now determine the mass of the water by taking the difference of the two masses. 

4. Set up the apparatus as in the diagram below.  When you are sure that everything is set up properly, record the temperature of the water very carefully and accurately.  Record data in chart.  Notify the teacher when you are ready and he or she will light your nut to be burned.  BE VERY CAREFUL WITH THE THERMOMETER; IT IS VERY DELICATE!!!

5. Immediately after the nut is lit, position the exterior can and soda can so that the bottom of the soda can is about 1 inch above the top of the nut. 

6. Record the highest temperature reached after the flames go out.  Make sure you stir the water gently to be sure you have an accurate temperature.  Record temperature in data table.  You can now calculate DT from the two temperatures (before and after burning). 

7. Use the heat equation to solve for the amount of heat given off by the nut (in Joules).  Convert Joules to calories by dividing by 4.184. 

8. Divide this number by the mass of the nut to get the calories/gram for the nut.  Compare this value to the accepted value listed in the 2^nd paragraph. 

9. Repeat the procedure two more times with peanuts and three times with almonds.
   
   
   
   
   Data Table: