The formula used in this table to work out the energy released is:
(CHO x 17) + (Protein x 17) + (Lipids x 34) = KJ/100g 100 = KJ/g
Plan
I plan to find out which crisp releases the most energy when respired. I will do this by putting the crisps in order of most energy released when burnt. I will do this by burning the chemical energy in each crisp into heat energy under a boiling tube of water, and measuring the temperature increase that results.
The pieces of equipment I will be using are; different crisps, a retort stand, two bosses and two clamps, five boiling tubes, scales, Bunsen burner, cup made from tin foil, measuring cylinder, bench mat, thermometer and weighing boat for scales.
Diagram
Variables
Input
The variable I will be changing is the crisp. I will change it by using a different make of crisp. I will be using 5 different crisps. These crisps will be; Smiths Salt ‘n’ Shake, Walkers Ready Salted, Walker Lites Ready Salted, Walker Lites Cheese and Onion, and Hula Hoops.
Output
I am measuring the temperature change of the water, I will also be measuring change in the mass of the crisp before and after it is burnt. I will measure the temperature of the water using an alcohol thermometer and the mass using a set of scales. I plan to do this 3 times for each crisp.
Controlled
I will keep the starting water temperature at 20 degrees Celsius by changing the water and test tube for each experiment and the starting volume of the water at 20cm3 because if it was less the water would just boil and evaporate so I will get no temperature change and if there is too much water it will take to long and the crisp would only heat the water a fraction. To do this I will always check the temperature is 20 degrees Celsius (room temperature) and I will use a measuring cylinder to measure 20ml of water for the boiling tube. Using a measuring cylinder is not a very accurate way of measuring the water instead using a glass pipette. I will also keep the distance between the crisp and the boiling tube 5cm because if I were to put it at a distance of 20cm for example most of the heat would be lost to the air and if it was 1-2cm the crisp would be smothered and the flame would go out due to lack of oxygen. Finally I will always light the crisp in the same way because doing it another way may cause the crisp to be away from the tube for a longer period of time cause more heat to be lost than in the previous experiment.
Method
- Set up equipment as shown in diagram.
- Take crisp weigh on scales, record mass on table and place crisp in tin foil cup. Record temperature of water.
- Light Bunsen burner, swivel clamp away from tube and light crisp.
- Once crisp is burning quickly swivel crisp back to tube without causing the flame to go out.
- Allow crisp to burn if flame goes out repeat steps 3&4.
- When crisp will no longer relight measure temperature of water and record on table. Then weigh mass of burned out crisp and record data.
- Repeat for other crisps.
Safety
To be safe I will wear goggles at all times, keep stools under benches, keep bunsen burner away from flammable objects and make sure that anything I have been burning has fully gone out before putting it in the bin.
Table Of Results
I am going to use a formula from my notes to calculate the average KJ per G released. Scientists have discovered that it takes 4.2 Joules of energy to heat 1cm cubed of water by 1°C. Therefore theoretically it should take 84 Joules to heat 20cm cubed of water by 1°C. The formula is 4.2 x Volume of water x Temp change = J/g
Mass Change of crisp
Here are my results for how much energy was released per gram.
XXX=anomalous result
Graphs And Tables
See graph paper.
Analysis
I found that the crisps that released the most energy were the Walkers Ready Salted. 2nd most energy came from the Hula Hoops and 3rd most from the Walkers Lites Ready Salted then the Walkers Lites Cheese and Onion, least most energy came from the Smiths Salt ‘n’ Shake.
These results prove my predictions very wrong. I think that this is because much of the heat was lost to the air when burning the crisp as well as the soot on the tube that if burned in pure oxygen would have created more heat, as would the fat that dripped off of the crisp.
Most of my repetitions for each crisp were quite close with the exception of about 3 results, so I am convinced this is enough data for my experimental results to be correct.
Evaluation
I think the results of mine that were anomalous were anomalous because my experiment was not very reliable at all most heat was either lost to the boiling tube, the clamp or the air.
Looking at my table comparing my experimental and predicted results I can see that my experiment was not performed fairly at all and these results have shown me my experiment had many errors.
As I have already said a lot of heat and energy was absorbed by the air, the clamp and the boiling tube. The soot on the boiling tube was part of the crisp so it takes some of the mass away without burning it, the soot can be burned in pure oxygen. Some of the crisps may have taken more energy to light. The smoke that came off of the crisps was hot and would of given energy but drifted off in to the air. There was also light energy given off but very little.
All of these errors are eliminated when the energy of the crisps is measured in the factory by using a Bomb calorimeter.
The Bomb Calorimeter (pictured above) does not allow heat to be absorbed by the air, as it is all trapped inside and has a heatproof platform. The soot is burned because the crisp is burnt in pure oxygen, they time how long it takes to light the crisp and use a constant amount of energy so they know how much energy has been used. The smoke and heat is fed through a coiled pipe to heat the water around it and by the time it reaches the top it is cold so no heat is lost. They also use exactly 1g of crisp.
