A student performed an experiment to compare the energy content of dry broad beans and dry soybeans - VCE - SSCE Chemistry - Question 8 - 2023 - Paper 1

The independent variable in the experiment is the type of legume used (dry broad beans vs. dry soybeans).

One precaution the student should take is to use a heatproof mat. This mitigates the risk of a laboratory fire by preventing the heat from the burning beans from igniting materials on the surface beneath the setup.

To calculate the energy change in the water, we use the formula:

$q = mc\Delta T$

where:

• m = mass of the water (300 mL = 299.1 g)
• c = specific heat capacity of water (4.18 J/g°C)
• ΔT = change in temperature (final temperature - initial temperature). Assuming the final temperature is 88.8 °C and initial temperature is 25 °C, we have:

$q = 299.1 imes 4.18 imes (88.8 - 25) = 299.1 imes 4.18 imes 63.8 \\ = 7992.61 J \\ \approx 8.0 \text{ kJ}$

The energy content per 100 g can be calculated from the total energy measured. Using the formula:

$\text{Energy content per 100 g} = \frac{(36 \times 17) + (20 \times 37) + (29 \times 16)}{100}$ we calculate this to be

$\text{Energy content} = \frac{(612 + 740 + 464)}{100} = 1816 \text{ kJ}$

An improvement could be to ensure better insulation was used on the outside container. This would allow for more accurate temperature readings as it would minimize heat loss to the surroundings, thus enhancing the temperature change measurement and leading to a more accurate calculation of energy content.

One possible error could arise from the student not allowing enough time for the temperature to stabilize before taking readings. This could lead to readings that are too high or too low, causing the calculated energy content to be inaccurate and higher than expected.

The energy content of soybeans is typically higher than that of broad beans. This may be attributed to the soybean's higher lipid and protein content, which contributes to a greater caloric value when combusted.