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CIE iGCSE Co-Ordinated Science C1.2 Diffusion Exam Style Questions Paper 4

CIE iGCSE Co-Ordinated Science Paper 4 - All Chapters

Question

The arrangement and movement of particles in solids, liquids and gases are different.
(a) Draw one line from each state of matter to the arrangement and movement of particles.
(b) A student tests the melting point of four different solids.
Table 2.1 shows their results.
State which of the four solids, A, B, C or D, is a mixture. Explain your answer.
(c) Table 2.2 shows the relative molecular mass, \(M_r\), of three different gases.
State which gas will diffuse fastest. Explain your answer.
(d) Sulfur dioxide is a common pollutant in the air.
(i) State the source of sulfur dioxide in the air.
(ii) State an adverse effect of sulfur dioxide in the air.
(e) Sulfur is used in the manufacture of sulfuric acid in the Contact Process. Complete and balance the equations for the Contact Process.
\( S + O_2 \rightarrow SO_2 \)
\( 2SO_2 + \text{……..} \rightleftharpoons \text{…..} \, SO_3 \)
\( \text{……} + SO_3 \rightarrow H_2S_2O_7 \)
\( H_2S_2O_7 + \text{…….} \rightarrow 2H_2SO_4 \)

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C1.1 — Solids, liquids and gases (Parts (a), (b))
• Topic C1.2 — Diffusion (Part (c))
• Topic C10.2 — Air quality and climate (Part (d))

▶️ Answer/Explanation

(a) 

In a solid, strong forces hold particles in fixed positions in a lattice, so they can only vibrate.
In a liquid, particles stay close together but the weaker forces let them move past one another.
In a gas, particles are far apart with negligible forces between them, so they move rapidly and randomly.

(b) Solid B; melts over a range of temperatures rather than at one sharp point

A pure substance melts at one fixed, sharp temperature.
Solid B melts over a range (81–88 °C) instead of at a single value, which is the signature of an impure substance/mixture.

(c) Ammonia, NH\(_3\); it has the lowest \(M_r\) (17), so it is the lightest/fastest-moving gas

Rate of diffusion is inversely related to the mass of the gas particles.
Since NH\(_3\) has the smallest relative molecular mass (17, compared with 44 for CO\(_2\) and 64 for SO\(_2\)), its particles move fastest and diffuse fastest.

(d)(i) Combustion of fossil fuels containing sulfur compounds

Sulfur impurities in coal and oil are oxidised to sulfur dioxide gas when these fuels are burned in power stations, vehicles, and industry.

(d)(ii) Causes acid rain (or causes breathing difficulties such as asthma)

Sulfur dioxide dissolves in atmospheric water to form dilute sulfurous/sulfuric acid, which falls as acid rain and damages buildings, water bodies and vegetation.
It also irritates the respiratory system, worsening conditions such as asthma.

(e) \(2SO_2 + O_2 \rightleftharpoons 2SO_3\); \(H_2SO_4 + SO_3 \rightarrow H_2S_2O_7\); \(H_2S_2O_7 + H_2O \rightarrow 2H_2SO_4\)

Sulfur dioxide is catalytically oxidised to sulfur trioxide in a reversible reaction.
Sulfur trioxide is then dissolved in concentrated sulfuric acid to form oleum (\(H_2S_2O_7\)), since SO\(_3\) reacts too violently with water directly.
The oleum is finally diluted carefully with water to give concentrated sulfuric acid.

Question

(a) Particles can be atoms, ions or molecules. Particles either form pure substances or mixtures.
Draw one line from each word to the correct definition. One has been done for you.
(b) Particles can diffuse at different rates.
Fig. 5.1 shows an experiment to investigate diffusion of gas particles.
Ammonia gas, \( \text{NH}_3 \), and hydrogen chloride gas, \( \text{HCl} \), diffuse along the tube. When the gases meet, they react to form a white cloud of ammonium chloride.
(i) The ammonium chloride forms at the end of the tube furthest from the ammonia. Explain why, in terms of the movement of molecules.
(ii) Calculate the volume occupied by \( 5.1 \, \text{g} \) of ammonia gas.
The molar gas volume at room temperature and pressure is \( 24 \, \text{dm}^3 \).
Show your working.
[\(A_r\) : H, 1; N, 14]

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C2.1 — Elements, compounds and mixtures (Part (a))
• Topic C1.2 — Diffusion (Part (b)(i))
• Topic C3.3 — The mole and the Avogadro constant (Part (b)(ii))

▶️ Answer/Explanation

(a) 

(b)(i) Ammonia molecules are lighter and diffuse faster

The molecular mass of ammonia (\( M_r = 17 \)) is less than that of hydrogen chloride (\( M_r = 36.5 \)).
Lighter molecules move faster and diffuse a greater distance in the same time, so ammonia travels further along the tube before meeting the hydrogen chloride, forming the cloud nearer the HCl end.

(b)(ii) \( 7.20 \, \text{dm}^3 \)

\( M_r \) of \( \text{NH}_3 = 14 + (3 \times 1) = 17 \).
moles of \( \text{NH}_3 = \dfrac{5.1}{17} = 0.3 \, \text{mol} \).
volume \( = 0.3 \times 24 = 7.2 \, \text{dm}^3 \).

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