IB Chemistry SL Structure 1: Models of the particulate nature of matter questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

Type

Multiple choice Written

Difficulty

Easy Medium Hard

Question 1

Paper 2Hard8 marks

A sample of ice is heated at constant pressure. Figure 1 shows the structural formula of the substance. The temperature is recorded at intervals.

Time / min	Temperature / °C
0.0	−8.2
2.0	−2.1
4.0	0.0
6.0	0.0
8.0	8.1
10.0	32.2

(a)

State the formula of each particle in the sample, using Figure 1.

[1]

(b)

Convert the temperatures recorded at 8.0 min and 10.0 min to kelvin, to the nearest kelvin.

[2]

(c)

Identify the time interval during which the sample is changing state.

[1]

(d)

A student concludes: “At 10.0 min, the average kinetic energy of the particles is about four times its value at 8.0 min, because 32.2 is about four times 8.1. The average kinetic energy also continues to increase from 4.0 to 6.0 min because the sample is still being heated.”

Evaluate both statements, using the data and your answer to (b).

[4]

Question 2

Paper 2Easy5 marks

A sample of chlorine is modelled as containing only the two isotopes shown in Figure 1. Use the mass numbers as the isotope masses when calculating the relative atomic mass.

(a)

State the number of neutrons in ${}^{37}_{17}\mathrm{Cl}$

[1]

(b)

State where the electrons are found relative to the nucleus in a chlorine atom.

[1]

(c)

Explain why ${}^{35}_{17}\mathrm{Cl}$ and ${}^{37}_{17}\mathrm{Cl}$ are isotopes.

[1]

(d)

Using Figure 1, determine the relative atomic mass of the chlorine sample. Give your answer to 3 significant figures.

[2]

Question 3

Multiple choiceHard1 mark

An enriched copper sample contains only $^{63}_{29}\mathrm{Cu}$ and $^{65}_{29}\mathrm{Cu}$ Treating the mass numbers as isotope masses, its relative atomic mass is 63.60. Which description gives both their abundances in the sample and the subatomic-particle counts in the corresponding $\mathrm{Cu}^{2+}$ ions?

Show answer and explanation

Answer: B. The abundance-weighted mean gives $63x+65(1-x)=63.60$ so the fraction of $^{63}\mathrm{Cu}$ is $x=0.70$ Both isotopes have 29 protons; their neutron numbers are $63-29=34$ and $65-29=36$ Each $2+$ ion has lost two electrons, leaving 27.

A: reverses the abundances, which would give a mean mass of 64.40.
C: treats the $2+$ charge as two extra electrons rather than two fewer.
D: reverses the subtraction for neutron number, assigning more neutrons to the lower-mass isotope.
Remember: Isotopes differ in neutron number; ion charge reflects electron gain or loss.

Question 4

Multiple choiceEasy1 mark

A sample contains $0.0400\ \text{mol}$ of $\mathrm{O_2}$ molecules. What is the number of oxygen atoms in the sample? Use $N_\mathrm{A}=6.02\times10^{23}\ \text{mol}^{-1}$

Show answer and explanation

Answer: C. Each $\mathrm{O_2}$ molecule contains two oxygen atoms. Thus, $0.0400\times6.02\times10^{23}\times2=4.82\times10^{22}$ oxygen atoms.

A: uses $0.00400\ \text{mol}$ and counts $\mathrm{O_2}$ molecules rather than oxygen atoms.
B: counts $\mathrm{O_2}$ molecules but omits the two oxygen atoms in each molecule.
D: shifts the amount one place too high, using $0.400\ \text{mol}$

Remember: multiply by the number of specified entities in each molecule when counting atoms.

Question 5

Paper 2Hard10 marks

A laboratory checks a powdered reference blend containing only paracetamol and caffeine. The structures of the two compounds are shown in Figure 1.

A sample of the blend has a mass of 1.6754 g and contains a total amount of 0.01000 mol of molecules. A quality-control note states that the two compounds are present in equal masses.

(a)

Use Figure 1 and the Ar values in the data booklet to determine the molecular formula and Mr of each compound.

[4]

(b)

Determine the amount, in mol, of each compound in the sample. Show your reasoning.

[4]

(c)

Calculate the mass of each compound in the sample and state whether the quality-control note is supported.

[2]

Question 6

Paper 2Hard12 marks

A laboratory is checking whether the ideal-gas model gives reliable volume estimates for gases in a transfer line. Samples of carbon dioxide and methane are measured at $280\ \mathrm{K}$ The table gives their measured molar volumes and the ideal-gas molar volume at each pressure.

Pressure / bar	Ideal-gas molar volume / dm³ mol⁻¹	Measured CO₂ molar volume / dm³ mol⁻¹	Measured CH₄ molar volume / dm³ mol⁻¹
1.00	23.3	23.1	23.2
5.00	4.66	4.54	4.63
10.0	2.33	2.14	2.29
20.0	1.16	0.94	1.11

(a)

Use Figure 1 to determine the molecular formula of each gas.

[2]

(b)

For an ideal-gas sample of $1.00\ \mathrm{mol}$ at $280\ \mathrm{K}$ and $20.0\ \mathrm{bar}$ calculate the molar volume. Give your answer in $\mathrm{dm^3\,mol^{-1}}$ to three significant figures. Use the ideal gas equation in the data booklet.

[2]

(c)

At $1.00\ \mathrm{bar}$ compare the measured molar volume of each gas with the ideal-gas value.

[2]

(d)

Explain why real gases are more likely to deviate from the ideal-gas model at low temperature and high pressure.

[2]

(e)

A technician argues that the ideal-gas model is equally reliable for carbon dioxide and methane at $280\ \mathrm{K}$ and $20.0\ \mathrm{bar}$ because the ideal molar volume is the same for both gases. Evaluate this argument using the table and Figure 1.

[4]

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