AS-Level AQA 2025 Chemistry Paper 1 – Mark Scheme (Inorganic and
Physical Chemistry)
1. Electron Configuration
Al atom: 1s² 2s² 2p⁶ 3s² 3p¹
Cr³⁺ ion: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³
2. Ion with 2+ Charge and Argon Configuration
Answer: Sr²⁺
3. Compound with 2+ and 3− Ions (Argon Configuration)
Answer: CaP
4. Smaller Ion: Na⁺ vs. Mg²⁺ (2 marks)
Mg²⁺ is smaller
Same shielding but Mg²⁺ has higher nuclear charge → stronger
attraction → smaller radius
5. First Ionisation of Sodium
Equation: Na(g) → Na⁺(g) + e⁻
6. Sulfur vs. Phosphorus Ionisation Energy (4 marks)
Sulfur: paired electrons in 3p orbital
Phosphorus: unpaired electrons
Electron pair repulsion in sulfur lowers ionisation energy
Less energy needed to remove paired electron
7. Reducing Burette Uncertainty (2 marks)
Use a larger mass of solid
Requires a larger titre → reduces % uncertainty
8. Preparing a 250 cm³ Solution (6 marks)
Weigh sample + bottle
Transfer solid to flask and reweigh bottle
Record mass difference
Physical Chemistry)
1. Electron Configuration
Al atom: 1s² 2s² 2p⁶ 3s² 3p¹
Cr³⁺ ion: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³
2. Ion with 2+ Charge and Argon Configuration
Answer: Sr²⁺
3. Compound with 2+ and 3− Ions (Argon Configuration)
Answer: CaP
4. Smaller Ion: Na⁺ vs. Mg²⁺ (2 marks)
Mg²⁺ is smaller
Same shielding but Mg²⁺ has higher nuclear charge → stronger
attraction → smaller radius
5. First Ionisation of Sodium
Equation: Na(g) → Na⁺(g) + e⁻
6. Sulfur vs. Phosphorus Ionisation Energy (4 marks)
Sulfur: paired electrons in 3p orbital
Phosphorus: unpaired electrons
Electron pair repulsion in sulfur lowers ionisation energy
Less energy needed to remove paired electron
7. Reducing Burette Uncertainty (2 marks)
Use a larger mass of solid
Requires a larger titre → reduces % uncertainty
8. Preparing a 250 cm³ Solution (6 marks)
Weigh sample + bottle
Transfer solid to flask and reweigh bottle
Record mass difference
