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CSEC Chemistry study materials
CSEC Chemistry study resources

CSEC Chemistry: Chemistry Content and Principles

CSEC Chemistry · Work through your exam, one topic at a time.

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Chemistry Content and Principles

Chemistry content and principles

This domain tests the core content of CSEC Chemistry: the particulate nature of matter, atomic structure and periodicity, bonding and structure, formulae and equations, the mole concept, acids, bases and salts, redox, rates and equilibrium, organic chemistry, metals and non-metals, and qualitative analysis. Questions reward correct terminology, balanced equations and explanations that link structure to observable properties.

Core rules

  • Particles and states: matter is made of moving particles; temperature affects average kinetic energy. Separation methods depend on physical differences such as boiling point, solubility or particle size.
  • Atoms and periodicity: proton number defines the element; nucleon number gives isotopes. Electron arrangement (for the first 20 elements, 2,8,8) determines group and period, and hence trends in reactivity and ion charge.
  • Bonding: ionic lattices contain oppositely charged ions; simple covalent molecules have weak intermolecular forces; giant covalent and metallic structures have different melting points and conductivity.
  • Equations and moles: balance equations by conserving atoms; include state symbols when asked. Use n = m/M, n = V/24 for gases at room temperature and pressure, and c = n/V for solutions; mole ratios come from the balanced equation.
  • Acids, bases and redox: acids donate protons; bases accept protons; neutralisation forms salt and water. In redox, oxidation is loss of electrons and reduction is gain; assign oxidation numbers to confirm changes.

Worked example

0.240 g of magnesium reacts completely with excess dilute hydrochloric acid. Calculate the volume of hydrogen produced at room temperature and pressure. (Mg = 24; molar volume = 24 dm3 mol−1.)

Balanced equation: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g). The mole ratio Mg:H2 is 1:1. n(Mg) = 0.240/24 = 0.0100 mol, so n(H2) = 0.0100 mol. V(H2) = 0.0100 × 24 = 0.240 dm3, or 240 cm3. The acid is in excess, so magnesium determines the amount of hydrogen.

Traps

  • Using an unbalanced equation and then taking a mole ratio from it.
  • Mixing up molar mass and relative atomic mass, or forgetting to convert cm3 to dm3.
  • Quoting 22.4 dm3 mol−1 when the question specifies room temperature and pressure rather than s.t.p.
  • Writing ionic formulae without balancing charges, such as MgCl instead of MgCl2.
  • Confusing oxidation and reduction, or saying a substance is oxidised without identifying electron loss.