Chemistry - Post-UTME Study Guide
Chemistry in the Post-UTME covers atomic structure, bonding, the periodic table, stoichiometry, acids and bases, and organic chemistry. Precision with formulae and units is usually what separates a correct answer from a near miss.
Core rules
- One mole contains 6.02 × 10²³ particles; molar mass is in g mol⁻¹.
- At STP, one mole of any gas occupies 22.4 dm³ (22.4 L).
- Ionic bonds transfer electrons; covalent bonds share electrons; metals are held by metallic bonding.
- Acids donate protons; bases accept protons; pH below 7 is acidic, above 7 is alkaline.
- In a balanced equation, coefficients give the mole ratio.
Worked example
What volume of CO₂ at STP is produced when 10 g of CaCO₃ is completely decomposed? CaCO₃ → CaO + CO₂. Molar mass of CaCO₃ = 40 + 12 + 3(16) = 100 g mol⁻¹. Moles = 10 ÷ 100 = 0.1 mol. The equation gives 1 mol CO₂ per 1 mol CaCO₃, so 0.1 mol CO₂ is produced. Volume = 0.1 × 22.4 = 2.24 dm³.
Traps
Do not use the coefficient of the wrong substance. Check whether the question says STP or room temperature; molar volume differs. Do not confuse empirical and molecular formulae. In redox, balance atoms and charge, not just atoms. Isotopes have the same chemical properties but different masses.