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Worksheet 1

States of matter and kinetic theory

IB MYP Chemistry · Matter · 31 marks · about 40 minutes

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NameClassDate
Answer in the spaces provided. Marks are shown in brackets; the parts follow the four MYP Sciences criteria. Use the mark scheme only after you have tried every question.

APart A — Knowing and understanding

Criterion A · 14 marks

1
Compare the arrangement and movement of particles in a solid and in a gas.[3 marks]
2
Name the change of state for (i) liquid to gas below the boiling point, (ii) solid directly to gas.[2 marks]
3
Octane melts at −57 °C and boils at 126 °C. State its physical state at (i) −80 °C, (ii) 20 °C, (iii) 150 °C.[3 marks]
4
Explain, in terms of particles, why the temperature of boiling water stays at 100 °C while it is heated.[3 marks]
5
In a diffusion tube experiment, a white ring of ammonium chloride forms closer to the hydrochloric acid end. Explain why.[3 marks]

BPart B — Inquiring and designing

Criterion B · 6 marks

A student investigates how temperature affects the rate of diffusion of a crystal of potassium manganate(VII) dissolving in water. The purple colour spreads out through the water.

6
Write a hypothesis, with a reason based on particle theory.[2 marks]
7
Describe a method that would allow the student to measure the rate of diffusion at five temperatures. Include how the dependent variable will be measured and what must be kept the same.[4 marks]

CPart C — Processing and evaluating

Criterion C · 7 marks

Temperature / °C2030405060
Time for colour to reach the edge / s480350270210165
8
Plot a graph of time against temperature and draw a smooth curve of best fit.[3 marks]
9
Describe the trend and explain whether it supports the hypothesis.[2 marks]
10
Suggest one source of error in judging “the colour reaching the edge”, and an improvement.[2 marks]

DPart D — Reflecting on the impacts of science

Criterion D · 4 marks

11
LPG cylinders are used for cooking in millions of homes. Using ideas about particles and pressure, explain why cylinders should be kept out of direct sunlight, and discuss one advantage and one risk of LPG compared with cooking on wood fires.[4 marks]
Mark scheme — 31 marks

1 [3]

  • Solid: regular arrangement, particles touching [1].
  • Gas: random arrangement, particles far apart [1].
  • Solid particles vibrate about fixed positions; gas particles move quickly and randomly in all directions [1].

2 [2]

  • (i) evaporation [1]
  • (ii) sublimation [1]

3 [3]

  • (i) solid [1]
  • (ii) liquid [1]
  • (iii) gas [1]

4 [3]

  • Energy is being supplied [1]
  • but it is used to overcome the attractions between particles so they can escape as gas [1]
  • not to increase their kinetic energy, so the temperature does not rise [1].

5 [3]

  • Ammonia molecules are lighter (Mr 17) than hydrogen chloride molecules (Mr 36.5) [1].
  • Lighter molecules move/diffuse faster at the same temperature [1].
  • So ammonia travels further before the two gases meet [1].

6 [2]

  • The higher the temperature, the faster the colour spreads [1].
  • Particles have more kinetic energy/move faster at higher temperature [1].

7 [4]

  • Heat/cool water to five temperatures (e.g. 20–60 °C) using a water bath, check with a thermometer [1].
  • Add one crystal of the same size to the centre of the same volume of water in identical beakers, without stirring [1].
  • Measure the time for the colour to reach a mark (e.g. the edge / 2 cm circle drawn on paper under the beaker), or the diameter of the coloured region after a fixed time [1].
  • Controls: crystal size, volume of water, beaker size, no stirring/disturbance; repeat three times [1].

8 [3]

  • Temperature on x, time on y, labels with units [1].
  • Points plotted correctly [1].
  • Smooth curve, decreasing and levelling [1].

9 [2]

  • As temperature increases, the time taken decreases, so diffusion is faster [1].
  • Supports the hypothesis: faster particles at higher temperature [1].

10 [2]

  • The edge of the colour is faint/gradual, so judging it is subjective [1].
  • Use a colorimeter or photograph at fixed times against a scale; same observer each time [1].

11 [4]

  • Heat raises particle speed and so the pressure inside the sealed cylinder; risk of leaks or bursting [1].
  • Advantage of LPG: cleaner indoor air (less smoke/particulates), less deforestation, faster cooking [1].
  • Risk: leaks can cause fires/explosions (gas denser than air collects low); cost and fossil-fuel CO2 [1].
  • Balanced judgement [1].

For Parts B–D, credit any scientifically valid answer that meets the same point; the answers given are models, not the only acceptable wording.