2.4 Exam Practice
Exam-style practice questions on From Models to Materials
Section B: Data Analysis (Paper 1B Style)
Calculator and Data Booklet permitted. Show all working clearly.
Question 1: The Bonding Triangle Classify
5 marksThe table shows electronegativity values for selected elements (Pauling scale).
| Element | Electronegativity |
|---|---|
| Cs | 0.79 |
| Na | 0.93 |
| Mg | 1.31 |
| Cl | 3.16 |
| F | 3.98 |
(a) For CsF and MgCl₂, calculate the electronegativity difference and the average electronegativity. [2]
(b) Using your answers, predict which compound is more ionic in character. Justify your answer. [1]
(c) Explain why the bonding in NaCl is considered to have some covalent character, even though it is predominantly ionic. [2]
Show Mark Scheme
(a) CsF: ΔEN = 3.98 - 0.79 = 3.19; Average EN = (3.98 + 0.79)/2 = 2.39 [1]
MgCl₂: ΔEN = 3.16 - 1.31 = 1.85; Average EN = (3.16 + 1.31)/2 = 2.24 [1]
(b) CsF is more ionic because it has a larger electronegativity difference (3.19 vs 1.85), placing it closer to the ionic corner of the bonding triangle [1]
(c) No bond is 100% ionic; the small, highly charged cation (Na⁺) can polarise the electron cloud of the larger anion (Cl⁻) [1]
This distortion pulls some electron density back towards the cation, introducing a degree of electron sharing (covalent character). This is described by Fajans' rules [1]
Section C: Structured Questions (Paper 2 Style)
Show all working. State answers with appropriate significant figures and units.
Question 2: Alloys and Their Properties Explain
4 marksSteel is an alloy of iron and carbon. Bronze is an alloy of copper and tin.
(a) Explain, at the atomic level, why alloys are harder and stronger than pure metals. [2]
(b) Explain why pure gold (24 karat) is rarely used for jewellery and is usually alloyed with other metals such as copper or silver. [2]
Show Mark Scheme
(a) In a pure metal, layers of identical atoms can slide over each other easily under stress [1]
In an alloy, atoms of different sizes disrupt the regular arrangement of layers, preventing them from sliding as easily. This makes alloys harder and more resistant to deformation [1]
(b) Pure gold is very soft and malleable because its atoms are all the same size and the layers slide easily [1]
Alloying with copper or silver introduces differently-sized atoms that lock the layers, increasing hardness and making the jewellery more durable for everyday wear [1]
Question 3: Addition Polymers Describe
4 marksPVC (polyvinyl chloride) is a widely used addition polymer.
(a) Draw the repeating unit of PVC, given that the monomer is chloroethene (CH₂=CHCl). [1]
(b) Explain the difference between addition polymerisation and condensation polymerisation. [2]
(c) State one environmental concern associated with addition polymers. [1]
Show Mark Scheme
(a) Repeating unit: -[CH₂-CHCl]n- showing single bonds only and continuation bonds at each end [1]
(b) Addition polymerisation: monomers with C=C double bonds join together by opening the double bond; no small molecule is lost [1]
Condensation polymerisation: monomers with two functional groups join together with the loss of a small molecule (usually water) [1]
(c) Addition polymers are generally non-biodegradable and persist in the environment, contributing to plastic pollution in landfill and oceans [1]
Question 4: Condensation Polymers HL Deduce
5 marksNylon-6,6 is a condensation polymer formed from hexanedioic acid (HOOC-(CH₂)₄-COOH) and hexane-1,6-diamine (H₂N-(CH₂)₆-NH₂).
(a) Identify the two functional groups involved in the condensation reaction. [1]
(b) Draw the repeating unit of nylon-6,6, showing the amide (peptide) linkage. [2]
(c) State the small molecule released during this condensation reaction. [1]
(d) Explain how condensation polymers could be broken down under certain conditions (hydrolysis). [1]
Show Mark Scheme
(a) Carboxylic acid (-COOH) and amine (-NH₂) [1]
(b) Repeating unit must show: the amide linkage (-CO-NH-), the -(CH₂)₄- chain from the diacid, and the -(CH₂)₆- chain from the diamine, with continuation bonds [1]
Correct amide bond drawn: C(=O)-N(-H) [1]
(c) Water (H₂O) [1]
(d) Hydrolysis breaks the amide linkage by the addition of water (often in the presence of acid or base catalyst), reversing the condensation reaction and regenerating the monomer functional groups [1]