Diffusion and Brownian Motion
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Diffusion and Brownian Motion — Free MYP4 Chemistry Practice Questions

1QuestionExamples of diffusion (perfume spreading, gas exchange)Concept Practice
3 marks~5 minCriterion B
An open perfume bottle is placed in a room. The rate at which the perfume vapour spreads is measured at three temperatures.

Temperature (°C)203040
Rate of diffusion (arbitrary units)2.03.55.5
a
Identify the trend shown by the data. [1]
b
Using particle theory, explain why increasing temperature affects the speed of perfume molecules. [1]
c
Analyse why faster-moving perfume molecules produce a higher rate of diffusion through air. [1]
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Solutions

2QuestionFactors affecting diffusion rate (temperature, particle size)Assessment Practice
4 marks~6 minCriterion C
Two identical beakers of water are placed on a bench. Beaker A is at 20∘C20^\circ\text{C}; Beaker B is at 60∘C60^\circ\text{C}. One drop of blue dye is added to each beaker simultaneously.
a
State which beaker shows faster diffusion of the dye. [1]
b
Explain how temperature affects the kinetic energy of particles and, as a result, the rate of diffusion. [2]
c
A student claims that doubling the temperature (from 20∘C20^\circ\text{C} to 40∘C40^\circ\text{C}) will exactly double the diffusion rate. Evaluate this claim. [1]
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Solutions

3QuestionExamples of diffusion (perfume spreading, gas exchange)Concept Practice
4 marks~6 minCriterion A
The diagram shows an alveolus in contact with a surrounding capillary. The alveolus contains a high concentration of O2O_2 molecules; the capillary blood contains a high concentration of CO2CO_2 molecules and a low concentration of O2O_2 molecules.
a
State the direction of net movement of O2O_2 molecules. [1]
b
Deduce the direction of net movement of CO2CO_2 molecules, and identify the driving force responsible. [1]
c
Explain, using particle theory, why O2O_2 moves from the alveolus into the blood rather than in the opposite direction. [2]
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Solutions

4QuestionFactors affecting diffusion rate (temperature, particle size)Assessment Practice
6 marks~9 minCriterion D
A chemical spill of volatile organic compounds (VOCs) occurs near a residential area. On a hot summer day (35∘C35^\circ\text{C}), VOCs diffuse rapidly into the air; on a cold winter day (5∘C5^\circ\text{C}), the same spill diffuses much more slowly.
a
Describe how the increase in temperature from 5∘C5^\circ\text{C} to 35∘C35^\circ\text{C} affects the kinetic energy of VOC molecules. [1]
b
Explain why the rate of diffusion of VOCs is greater at 35∘C35^\circ\text{C} than at 5∘C5^\circ\text{C}. [2]
c
Analyse the health implications for nearby residents on the hot day compared with the cold day, considering both the rate at which hazardous concentrations build up and the time available for protective action. [3]
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Solutions

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