Edexcel GCSE Chemistry: Principles of Chemistry 1

Key Takeaways for GCSE Chemistry Revision

1. States of Matter & Particle Theory

Key Concepts:

• Melting (Solid → Liquid):
  • Process: Particles gain energy, vibrate more, and break free from fixed positions.
  • Example: Ice (solid) → Water (liquid).
  • Tip: Describe both arrangement (fixed → random) and movement (vibrate → slide past each other).
• Evaporation/Boiling (Liquid → Gas):
  • Process: Particles gain enough energy to overcome intermolecular forces.
  • Example: Water boils → Water vapour forms.
  • Common Mistake: Confusing evaporation (surface process) with boiling (bulk process).
• Condensation (Gas → Liquid):
  • Process: Particles lose energy, move closer, and form bonds.
  • Example: Water vapour → Droplets on a cold surface.
  • Tip: Use terms like energy loss and random → less random arrangement.

Example Question (Page 1):

“Explain why the water level drops after boiling.”
Answer: Particles gain kinetic energy, move faster, escape as gas (water vapour), reducing the liquid volume.

2. Atomic Structure & Isotopes

Key Rules:

• Atomic Number (Z): Number of protons (defines the element).
• Mass Number (A): Protons + Neutrons.
• Isotopes: Atoms of the same element with different neutron numbers.

Example (Page 5):
Chlorine-35 vs. Chlorine-37:

• Both have 17 protons, but 18 vs. 20 neutrons.
• Relative Atomic Mass (Aᵣ):
  Ar=(3×35)+(1×37)4=35.5Ar​=4(3×35)+(1×37)​=35.5

Common Mistakes:

• Confusing mass number with relative atomic mass.
• Forgetting isotopes have identical chemical properties (same electrons).

Tip: Use the Periodic Table to find atomic numbers and groups.

3. The Periodic Table

Key Relationships:

• Group Number = Outer Electrons (e.g., Group 2 → 2 outer electrons).
• Period Number = Number of Electron Shells.

Example (Page 4):

“Name an element in the same group as carbon.”
Answer: Silicon (Group 4).

Tips:

• Elements in the same group have similar chemical properties (e.g., Mg and Ca both react vigorously with water).
• Use electronic configurations to predict reactivity (e.g., noble gases have full outer shells).

Common Mistake: Confusing group (vertical) with period (horizontal).

4. Chemical Calculations

Formulas to Memorise:

1. Moles (n):
   n=mass (g)molar mass (g/mol)n=molar mass (g/mol)mass (g)​
   Example: Moles of Mg in 6g:
   n=624=0.25 moln=246​=0.25 mol
2. Gas Volume at RTP:
   Volume (dm3)=n×24Volume (dm3)=n×24
3. Concentration:
   Concentration (mol/dm3)=nvolume (dm3)Concentration (mol/dm3)=volume (dm3)n​

Example (Page 7):

“Calculate the volume of H₂ gas produced from 0.1 moles of Mg.”
Answer:
Volume=0.1×24=2.4 dm3Volume=0.1×24=2.4 dm3

Common Errors:

• Forgetting units (e.g., mol/dm³).
• Misapplying molar ratios in equations (e.g., 1 mole Mg → 1 mole H₂).

Tip: Always write the balanced equation first!

5. Practical Evidence for Particle Theory

Key Experiments:

• Diffusion (Page 3): Potassium manganate(VII) in water spreads due to random particle movement.
• Dilution (Page 3): Repeated dilution shows particles are tiny (still present even when colour fades).

Example Explanation:

“Why does dilution support small particle size?”
Answer: Even after multiple dilutions, particles remain (colour visible), proving they are indivisible and extremely small.

6. Electronic Configurations

Rules:

• Electrons fill shells in order: 2, 8, 8, 18.
• Example: Fluorine (Atomic Number 9):
  2,72,7 (not 2, 8, 7 – total electrons = 9).

Tip: Use the Periodic Table to check configurations.

Final Tips for Success

1. Practice Past Papers: Identify patterns in question styles (e.g., 3-mark explanations often require arrangement, movement, energy).
2. Units Matter: Always include units (e.g., g, mol, dm³).
3. Keyword Glossary: Learn definitions (e.g., condensation, isotope, mole).
4. Double-Check Calculations: Avoid arithmetic errors (e.g., H2SO4=2+32+(16×4)=98H2​SO4​=2+32+(16×4)=98).

50 GCSE Chemistry Questions

UK-style English | Detailed Answers Included

Section 1: States of Matter & Particle Theory

1. a) Name the process when solid ice turns to liquid water. b) Describe the changes in particle arrangement and movement during this process. (3 marks)
2. After boiling water for 5 minutes, the water level drops. Explain this observation in terms of particle energy and movement. (4 marks)
3. a) Name the process when water vapour condenses on a cold surface. b) Describe how particle energy and arrangement change during this process. (3 marks)
4. Describe the arrangement and movement of particles in a) solid ice, b) liquid water, and c) water vapour. (6 marks)

Section 2: Atomic Structure & Isotopes

5. a) Define atomic number. b) How is it determined using the Periodic Table? (2 marks)
6. An atom has 6 protons and 6 neutrons. a) State its atomic number. b) Calculate its mass number. (2 marks)
7. Chlorine-35 and chlorine-37 are isotopes. a) What do these numbers represent? b) State one similarity and one difference between them. (3 marks)
8. A sample of chlorine contains 75% chlorine-35 and 25% chlorine-37. Calculate its relative atomic mass. (3 marks)
9. a) Define isotope. b) Explain why isotopes have identical chemical properties. (3 marks)

Section 3: The Periodic Table

10. An element has the electronic configuration 2,8,4. a) Identify its group. b) Name another element in the same group. (2 marks)
11. a) Which group contains elements with full outer electron shells? b) Why are these elements unreactive? (2 marks)
12. Magnesium and calcium are in the same group. a) Draw their electronic configurations. b) Explain why they have similar reactivity. (4 marks)
13. a) Name two elements in Period 3. b) State the number of electron shells in a Period 3 element. (2 marks)
14. a) Why do Group 1 metals become more reactive down the group? b) Name a Group 1 metal. (3 marks)

Section 4: Chemical Calculations

15. Calculate the relative formula mass (RFM) of: a) H2SO4H2​SO4​, b) MgSO4MgSO4​. (2 marks)
16. A student dissolves 4.8 g of magnesium in sulfuric acid. Calculate the moles of magnesium used. (2 marks)
17. Using the equation Mg+H2SO4→MgSO4+H2Mg+H2​SO4​→MgSO4​+H2​, calculate the volume of hydrogen gas produced at RTP from 0.2 moles of Mg. (2 marks)
18. 100 tonnes of calcium carbonate decomposes into calcium oxide. Calculate the mass of carbon dioxide produced. (3 marks)
19. A solution contains 0.88 g of CO2CO2​ dissolved in 2 dm³ of water. Calculate the concentration of carbonic acid (H2CO3H2​CO3​) in mol/dm³. (4 marks)

Section 5: Practical Work & Evidence for Particle Theory

20. Describe how the diffusion of potassium manganate(VII) in water provides evidence for particle theory. (3 marks)
21. A student dilutes a solution 10 times repeatedly until the colour disappears. Explain how this supports the idea that particles are very small. (3 marks)
22. a) What is simple distillation used for? b) Describe the arrangement of particles in the condenser during distillation. (3 marks)
23. After shaking a potassium manganate(VII) solution, the colour spreads evenly. Explain this using particle theory. (2 marks)

Section 6: Electronic Configurations

24. a) State the electronic configuration of fluorine (atomic number 9). b) How many outer electrons does it have? (2 marks)
25. Astatine is in Group 7. a) Predict its number of outer electrons. b) Explain your answer. (2 marks)
26. Draw the electronic configuration of a) magnesium, b) argon. (2 marks)
27. a) Why is argon unreactive? b) Compare its reactivity with magnesium. (3 marks)

Answers

Section 1: States of Matter

1. a) Melting. b) Particles vibrate more, break free from fixed positions; arrangement becomes random, particles slide past each other.
2. Particles gain kinetic energy, move faster, escape as gas (water vapour), reducing liquid volume.
3. a) Condensation. b) Particles lose energy, move closer, form bonds; arrangement becomes less random.
4. a) Fixed, vibrating in place. b) Random, sliding past each other. c) Random, fast-moving, far apart.

Section 2: Atomic Structure

5. a) Number of protons. b) Periodic Table lists elements by atomic number.
6. a) 6. b) 6+6=126+6=12.
7. a) Mass numbers. b) Same protons/electrons; different neutrons.
8. Ar=(75×35)+(25×37)100=35.5Ar​=100(75×35)+(25×37)​=35.5.
9. a) Atoms with same protons but different neutrons. b) Same electrons determine chemical properties.

Section 3: Periodic Table

10. a) Group 4. b) Silicon.
11. a) Group 0 (noble gases). b) Full outer shells; no need to gain/lose electrons.
12. a) Mg: 2,8,2; Ca: 2,8,8,2. b) Both have 2 outer electrons → similar reactivity.
13. a) Sodium, aluminium. b) 3 shells.
14. a) Outer electron further from nucleus → easier to lose. b) Sodium.

Section 4: Calculations

15. a) 2(1)+32+4(16)=982(1)+32+4(16)=98. b) 24+32+4(16)=12024+32+4(16)=120.
16. n=4.824=0.2 moln=244.8​=0.2 mol.
17. Volume=0.2×24=4.8 dm3Volume=0.2×24=4.8 dm3.
18. Moles of CaCO3=100100=1 molMoles of CaCO3​=100100​=1 mol. Mass of CO2=1×44=44 tonnesCO2​=1×44=44 tonnes.
19. i) Moles of CO2=0.8844=0.02 molCO2​=440.88​=0.02 mol. ii) Concentration = 0.022=0.01 mol/dm320.02​=0.01 mol/dm3.

Section 5: Practical Work

20. Particles move randomly, spreading out without external force → evidence for kinetic theory.
21. Even after dilution, particles remain (colour visible) → too small to be divided further.
22. a) Separate liquids with different boiling points. b) Particles lose energy, condense into liquid.
23. Particles collide and move randomly until evenly distributed.

Section 6: Electronic Configurations

24. a) 2,7. b) 7.
25. a) 7. b) Group 7 elements have 7 outer electrons.
26. a) Mg: 2,8,2. b) Ar: 2,8,8.
27. a) Full outer shell. b) Mg is reactive (loses electrons); Ar is unreactive.