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Energetics

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Question 4

A student investigated the temperature change when magnesium ribbon is added to dilute hydrochloric acid. Their experimental plan was:

  • Pour 80 cm380\text{ cm}^380 cm3 of dilute hydrochloric acid into a polystyrene cup.
  • Measure the starting temperature of the acid.
  • Add 0.35 g0.35\text{ g}0.35 g of magnesium ribbon, stir, and record the maximum temperature reached.

Here are the student's results:

  • Volume of dilute hydrochloric acid = 80 cm380\text{ cm}^380 cm3
  • Mass of magnesium ribbon = 0.35 g0.35\text{ g}0.35 g
  • Starting temperature = 18.2∘C18.2^\circ\text{C}18.2∘C
  • Maximum temperature reached = 36.7∘C36.7^\circ\text{C}36.7∘C
a.

Why is it better to use a polystyrene cup rather than a glass beaker for this experiment?

[1]
b.

The equation for the reaction is:

Mg(s)+2HCl(aq)→MgCl2(aq)+H2(g) \text{Mg}(s) + 2\text{HCl}(aq) \rightarrow \text{MgCl}_2(aq) + \text{H}_2(g) Mg(s)+2HCl(aq)→MgCl2​(aq)+H2​(g)

Suggest one observation, other than the change in temperature, that could be made during this reaction.

[1]
c.

State whether this reaction is exothermic or endothermic, and justify your response.

[2]
d.

Calculate the heat energy change (in Joules) in this experiment using the expression:

heat energy change=volume of solution×4.2×temperature change \text{heat energy change} = \text{volume of solution} \times 4.2 \times \text{temperature change} heat energy change=volume of solution×4.2×temperature change
[3]

Energetics Questions

  1. IGCSE
  2. /Chemistry
  3. /Energetics