AQA GCSE Chemistry Chemistry Paper 1 (Foundation), June 2022: Question 2

✅ Correct Answer

Element [1 mark]

💡 Key Knowledge

An element contains only one type of atom. Hydrogen exists naturally as diatomic molecules (H₂), but because both atoms are identical, it is still purely an element.

❌ Common Errors

Confusing molecules with compounds. Because hydrogen gas is written as H₂, some students mistakenly classify it as a compound.

✅ Correct Answers

• 02.2 (Mixture of compounds): A [1 mark]
• 02.3 (Mixture of elements): B [1 mark]

💡 Key Definitions

• Compound: Two or more different types of atom chemically bonded.
• Mixture: Two or more different substances not chemically combined.
• In Box A, all particles are compounds, but they are not all identical → mixture of compounds.
• In Box B, each unit contains only one element type → mixture of elements.

🧠 Exam Technique

Check each particle individually:

1. Are different atom colours touching? Yes = compound.
2. Are all groups identical? No = mixture.

✅ Correct Answer

filtration (or filtering) [1 mark]

💡 Key Knowledge

Filtration separates an insoluble solid from a liquid. Sand particles are too large to pass through the filter paper pores and remain as residue, while water passes through as the filtrate.

🧠 Examiner Insight

A simple description like "pouring through filter paper and funnel" is allowed by the mark scheme, but using the specific scientific term filtration is quicker and guarantees the mark.

📐 Data Analysis (02.5)

Table of boiling points:

• Liquid A: 97 °C
• Liquid B: 138 °C
• Liquid C: 78 °C ← Lowest
• Liquid D: 118 °C

First to distil: The substance with the lowest boiling point evaporates and reaches the top first.

✅ Correct Answers

• 02.5: C (or allow 78 °C ) [1 mark]
• 02.6: increases (or becomes warmer / hotter) [1 mark]

💡 Why does water temperature rise? (02.6)

The condenser cools hot vapour to turn it back into liquid (condensation). During condensation, the hot vapour transfers thermal energy to the cold cooling water jacket, causing the water's temperature to increase.

❌ Common Errors

Writing that the temperature decreases because students think of the condenser as "cooling things down" without realising heat is absorbed by the water.

✅ Correct 2-Step Answer

1. Step 1: Heat the solution until the crystallisation point is reached (or to reduce the volume / evaporate some water / until crystals start to form). [1 mark]
2. Step 2: Leave the solution to cool and crystallise. [1 mark]

🧠 Exam Technique: "Describe how..."

To secure both marks in crystallisation questions, you must show two distinct stages:

• Evaporation/heating to concentrate the solution.
• Cooling/standing to allow crystals to grow slowly.

❌ Common Misconceptions & Lost Marks

Heating to complete dryness: Heating until all water is gone produces a powdery solid, can cause thermal decomposition, and only earns a maximum of 1 mark as a fallback allowance. Always state to leave to cool/crystallise!