Experiment 6.1

Experiment 6.1: Determining the energy value in food samples

Purpose: To determine the energy value in food f ood samples Problem statement: What are the energy values in food samples? Hypothesis: The energy values in different food samples are different. Variables: Manipulated Manipulated variable variable : Food type Responding Responding variable : The rise of temperature temperature in water (energy (energy values) Control variable

: Mass of water

Materials: Distilled water, a peanut (whole), plasticine, cotton wool Apparatus: A boiling tube, a thermometer (0-100 oC), a retort stand, a pin (5-8 cm long), a measuring cylinder, a Bunsen burner, an electronic balance Technique: Measure the rise in temperature t emperature by using a thermometer. Measure the mass of the food samples by using electronic balance. Procedure: DRAW THE APPARATUS

1. 2. 3. 4. 5. 6. 7.

The peanut is weighed and its weight is recorded. 20ml of distilled water is poured into a boiling tube. The boiling tube is clamped to a retort stand. The initial temperature of the water in the boiling tube is recorded. The thermometer is kept in place by cotton wool. The peanut is spiked firmly to the end of a pin which is mounted on some plasticine. The peanut is ignited with by holding it to the flame of a Bunsen burner. The burning peanut immediately placed beneath the boiling tube to heat the water. 8. The water is stirred gently with the thermometer. 9. The final temperature, that is, the highest temperature, is recorded as soon as the peanut has stopped burning. 10. The energy value of the peanut is calculated using the following formula: 11. -1o -1

o

Energy value of peanut = 4.2 (Jg C ) x mass of water (g) x increase in temperature ( C)

-1

(kJ g )

Mass of peanut (g) x 1000

Results: Mass of peanut (g) Mass of water (g) (assuming that 1 ml of water weights 1 g) Initial temperature of water ( oC) Final temperature of water ( oC) Increase in temperature (oC)

x  20

t1 t2 t2 - t1 = y 

Heat produced by 1 g of burning peanut = 4,2 x 20.0 x y 

-1

kJ g

X  x 1000

Discussion: 1. To obtain a more accurate result, a. The temperature must be measure accurately. The thermometer must not be allowed to touch the base of the boiling tube. Water in the boiling tube must be stirred to ensure the heat is distributed evenly. b. The food must be oxidized completely by making sure the flames does not extinguish too quickly. c. A shield is used to enclose the boiling tube to reduce heat loss to the surroundings. d. The distance between the food and the boiling tube must not be too far. 2. When the peanut is burnt, heat energy is released.

3. In this experiment, assumptions are made. It is assumed that the water absorbs all the energy that is released from the oxidation of the food sample. However, in reality, not all the energy released by the peanut is used to heat the water. Thus, the result obtained from this experiment is less than the actual value. This is due to the fact that energy loss in the form of light and heat when the food burns. Besides, some of the energy is also absorbed by the boiling tube. 4. The knowledge of energy value in food samples is important since it helps us to plan our diet according to our daily energy requirements and to choose our food wisely. 5. The class of food with the highest energy value is lipid. Conclusion: Hypothesis is accepted. The energy values in different food samples are different.

The energy value of cashew nut is different from the energy value of peanut. Cashew nut has a higher energy value than peanut. The rise in temperature for cashew nut is higher than peanut. Therefore, the energy value for the cashew nut (7.2) is higher than the peanut.