Stoichiometry
- Limiting reagent, yield, concentration
PAU Chemistry exam (Catalonia)
Always go data → balanced equation → moles → requested quantity. A wrong formula can sink a whole part.
Almost every calculation is data → balanced equation → moles → requested quantity. Formulation errors sink whole parts.
Typical paper structure
- Nomenclature, stoichiometry, equilibrium, acid–base, redox; sometimes organic or kinetics.
- Linked parts: rescue later parts with a stated assumption if needed.
- States and significant figures count.
What Chemistry papers actually test
Structure and bonding
- Periodic trends
- VSEPR when asked
Equilibrium and acid–base
- Kc/Kp
- Weak vs strong acids
Redox and organic
- Ion-electron method
- Functional groups
Worked example: limiting reagent
8.0 g CH₄ react with 32 g O₂: CH₄ + 2 O₂ → CO₂ + 2 H₂O. Grams of CO₂? (C=12, H=1, O=16)
- n(CH₄)=0.50 mol, n(O₂)=1.00 mol — exact stoichiometric match.
- n(CO₂)=0.50 mol → 22 g.
22 g of CO₂.
Worked example: weak-acid pH
0.10 M ethanoic acid, Ka = 1.8×10⁻⁵. Find pH. Why is [H⁺] ≠ 0.10?
- Ka = x²/0.10 → x ≈ 1.34×10⁻³ → pH ≈ 2.87.
- Treating it as strong gives pH = 1.00 — a concept fail.
pH ≈ 2.87.
Common mark-losers
- Unbalanced equation
- Weak acid treated as strong
- Kc with pressures
What markers look at first
- Balanced equation before any number
- Correct K expression
- Sensible significant figures
Eight-week Chemistry plan
Fifteen minutes of naming every day. Timed calculations from week 3.
Week 1
Nomenclature daily.
Week 2
Limiting reagent and yield.
Weeks 3–4
Kc, Kp, Le Chatelier.
Week 5
Acid–base and hydrolysis.
Week 6
Redox.
Weeks 7–8
Organic plus two full papers.
LETSE method
- 15-minute naming drill
- PAU-style equilibrium in groups of 6, Tortosa or online
FAQ
Is nomenclature always tested?
Often yes, or you must write species correctly inside a calculation.
Do you teach this in Tortosa?
Yes, groups of 6 and online.
Periodic table allowed?
Bring the paper authorised for that sitting. Use masses given in the question.
Does Chemistry weight health degrees?
Heavily. Check the official table and the grade calculator.
Want marked practice?
PAU Chemistry in Tortosa and online.