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9 marksEnergetics

CSEC Chemistry · May/June 2015 · Paper 2 · Question 1(b)(i)

A student conducted an experiment to determine the heat of combustion of candle wax (a mixture of solid hydrocarbons) using the apparatus shown in Figure 1. The procedure involved weighing a conical flask, adding water, recording initial temperature, weighing the candle and watch-glass, lighting the candle to heat the flask's contents for 15 minutes, recording the highest temperature, and reweighing the cooled candle and watch-glass. Results for masses and temperatures are shown in Figure 2.

Use the readings shown in Figure 2 to complete Table 1.

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Other parts of this question

  1. 1(a)(i)List TWO natural sources of hydrocarbons.[2 marks]
  2. 1(a)(ii)Name ONE hydrocarbon, other than wax, that can be used as fuel.[1 mark]
  3. 1(b)(ii)Assuming that the heat absorbed by the conical flask = (mass of the conical flask) × (0.861 J g⁻¹ °C⁻¹) × (temperature change), calculate the heat absorbed by…[1 mark]
  4. 1(b)(iii)Assuming that the heat absorbed by the water = (mass of water in the conical flask) × (4.2 J g⁻¹ °C⁻¹) × (temperature change), calculate the heat absorbed by…[1 mark]
  5. 1(b)(iv)Calculate the TOTAL heat absorbed by the calorimeter. Total heat absorbed by the calorimeter = (heat absorbed by the conical flask) + (heat absorbed by water…[1 mark]
  6. 1(b)(v)Calculate the heat of combustion of the candle wax. Heat of combustion = (total heat absorbed by the calorimeter) / (mass of candle burnt)[1 mark]
  7. 1(b)(vi)What was the role of the can in this experiment?[1 mark]
  8. 1(c)(i)Complete Table 2 by inserting the inferences or observations as necessary for the test: Q is heated strongly in a boiling tube. A glowing splint is placed at…[3 marks]
  9. 1(c)(ii)Complete Table 2 by inserting the inferences or observations as necessary for the test: Dilute HCl is added in excess to Q and the mixture warmed. To the…[2 marks]
  10. 1(c)(iii)Complete Table 2 by inserting the inferences or observations as necessary for the test: Dilute nitric acid followed by a few drops of silver nitrate solution…[3 marks]

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