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1.1 Exam Practice

Exam-style practice questions on Particulate Nature of Matter

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Section B: Data Analysis (Paper 1B Style)

Calculator and Data Booklet permitted. Show all working clearly.

Question 1: Heating Curve Analysis Analyse

4 marks

A student heats a sample of a pure substance from −20 °C to 120 °C at a constant rate. The heating curve below shows the temperature recorded every minute.

Heating curve data: the temperature rises from −20 °C to 0 °C over 2 minutes, remains at 0 °C for 3 minutes, rises from 0 °C to 100 °C over 5 minutes, remains at 100 °C for 4 minutes, then rises to 120 °C over 1 minute.

(a) Identify the substance and justify your answer using evidence from the data. [2]

(b) Explain why the temperature remains constant during the two plateau regions. [2]

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(a) The substance is water [1]

Evidence: melting point = 0 °C and boiling point = 100 °C, which are the characteristic values for water [1]

(b) During a change of state, the energy supplied is used to overcome the intermolecular forces / break the bonds between particles [1]

The kinetic energy of the particles does not change, so the temperature remains constant [1]

Examiner tip: A common mistake is stating that "energy is used to change the state." This is too vague. You must specify that the energy overcomes intermolecular forces, and that kinetic energy remains unchanged during a phase change.

Section C: Structured Questions (Paper 2 Style)

Show all working. State answers with appropriate significant figures and units.

Question 2: Temperature Conversion Calculate

3 marks

Gallium (Ga) is a post-transition metal that melts just above room temperature at 29.8 °C. It boils at 2204 °C.

(a) Convert the melting point of gallium to Kelvin. [1]

(b) Calculate the liquid range of gallium in Kelvin. [1]

(c) Suggest why gallium has such an unusually low melting point for a metal. [1]

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(a) \(29.8 + 273.15 =\) 302.95 K (Accept 303.0 K) [1]

(b) \(2204 - 29.8 =\) 2174.2 K (or equivalent in °C, then convert) [1]

(c) Gallium has relatively weak metallic bonding / low lattice enthalpy due to its small atomic radius and the way its atoms pack in the crystal structure [1]

Examiner tip: For temperature conversions, always use \(T(K) = T(°C) + 273.15\). The IB data booklet gives this relationship. Be precise with significant figures.

Question 3: States of Matter Explain

4 marks

(a) Using the kinetic molecular theory, explain why gases are compressible but liquids are not. [2]

(b) When perfume is sprayed in one corner of a room, it can soon be detected throughout the room. Use the kinetic molecular theory to explain this observation. [2]

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(a) In gases, particles are far apart with large spaces between them [1]

In liquids, particles are close together with very little space, so they cannot be pushed closer [1]

(b) The perfume particles are in constant random motion / diffusion occurs [1]

They collide with air molecules and spread out to fill the available space [1]

Examiner tip: When explaining diffusion, always mention both random motion and collisions with other particles. Simply saying "particles move" without specifying the random nature will not earn full marks.

Question 4: Separation Techniques Suggest

5 marks

A chemist has a mixture containing dissolved sodium chloride, sand and water.

(a) Outline a procedure to obtain a pure, dry sample of sodium chloride from this mixture. [3]

(b) State how you could confirm that the sodium chloride obtained is pure. [1]

(c) Suggest one reason why the actual yield of sodium chloride may be less than expected. [1]

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(a)

  • Filter the mixture to remove the insoluble sand [1]
  • Collect the filtrate containing dissolved NaCl [1]
  • Evaporate the water / crystallise the NaCl from the filtrate [1]

(b) Measure the melting point: if it is sharp and matches the known value (801 °C), the sample is pure [1]

(c) Any one of: some NaCl may remain on the filter paper / some solution may be lost during transfer / some NaCl may remain dissolved and not crystallise [1]

Examiner tip: The IB command word "Outline" means give a brief account. You do not need to explain why each step works, just state what you would do. However, using correct terminology like "filtrate" and "crystallise" demonstrates strong understanding.
Links to: 1.4 Counting Particles (yield and mole calculations)

Question 5: Kinetic Molecular Theory Discuss

4 marks

The kinetic molecular theory is a model used to explain the behaviour of matter in different states.

(a) State two assumptions of the kinetic molecular theory for an ideal gas. [2]

(b) Explain why the behaviour of real gases deviates from ideal behaviour at high pressures and low temperatures. [2]

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(a) Any two of:

  • Gas particles have negligible volume compared to the total volume [1]
  • There are no intermolecular forces between particles [1]
  • Collisions between particles are perfectly elastic [1]
  • The kinetic energy is proportional to the absolute temperature [1]

(b) At high pressures, the volume of the gas particles becomes significant relative to the total volume / particles are forced closer together [1]

At low temperatures, the particles move more slowly and intermolecular forces become significant / attraction between particles cannot be ignored [1]

Examiner tip: This question links directly to 1.5 (Ideal Gases). When explaining deviations, always state which assumption breaks down and why it breaks down under those conditions. Vague answers like "the gas stops being ideal" earn no marks.
Links to: 1.5 Ideal Gases (ideal gas law and deviations)
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