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a. The label on a packet of dry biscuits gives the following nutritional information - VCE - SSCE Chemistry - Question 9 - 2004 - Paper 1
Question 9
a. The label on a packet of dry biscuits gives the following nutritional information. serving size 35 g protein 3.7 g fat - saturated 0.8 g - unsaturated 0.1 g ... show full transcript
Worked Solution & Example Answer:a. The label on a packet of dry biscuits gives the following nutritional information - VCE - SSCE Chemistry - Question 9 - 2004 - Paper 1
Step 1
Given that the energy available to the body per gram of - protein is 16 kJ - fat is 37 kJ - digestible carbohydrate is 17 kJ calculate the total possible energy available to the body per gram of biscuit.
Answer
To calculate the total possible energy available to the body per gram of biscuit, we need to consider the contributions from protein, fat, and digestible carbohydrates.
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Energy from Protein: The energy contribution from protein per gram is 16 kJ. Given that there are 3.7 g of protein in the biscuit, the total energy from protein is:
Energy_{protein} = 3.7 imes 16 = 59.2 ext{ kJ}
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Energy from Fat: The energy contribution from fat per gram is 37 kJ. The total energy from fat (considering both saturated and unsaturated fat) is calculated as:
Energy_{fat} = (0.8 + 0.1) imes 37 = 0.9 imes 37 = 33.3 ext{ kJ}
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Energy from Digestible Carbohydrates: The total digestible carbohydrate in the biscuit is 26.0 g, with each gram providing 17 kJ:
Energy_{carbohydrates} = 26.0 imes 17 = 442.0 ext{ kJ}
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Total Energy Calculation: Now we can sum all the contributions to find the total possible energy:
Therefore, the total possible energy available to the body per gram of biscuit is approximately 534.5 kJ.
Step 2
A sample of the biscuit is burned in a bomb calorimeter to determine its energy value. The result indicated that 1 gram of biscuit releases 17 kJ. Give a possible explanation for the difference between this value and that calculated in part i.
Answer
The discrepancy between the calculated energy value of approximately 534.5 kJ per gram and the measured value of 17 kJ per gram from the bomb calorimeter can be attributed to several factors:
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Incomplete Combustion: In a bomb calorimeter, the sample may not undergo complete combustion, leading to an underestimation of the total energy released. Some components, like cellulose, may not combust entirely.
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Measurement Conditions: The conditions under which the calorimeter operates might not fully replicate the energetic value that is available to the body when metabolizing the biscuit.
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Digestibility: The calorimeter measures the energy accessible during combustion, while the energy calculated in part i considers only energy taken up by the body. Components like dietary fiber may contribute to calorimetry results but are not metabolized by human digestion, thus resulting in a lower measured value.
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Sample Variation: Variability in the biscuit sample's composition may lead to differences in energy values, reflecting diverse proportions of proteins, carbohydrates, and fats.