Chemistry - Physical, Inorganic and Applied Diploma Content
What the section tests
Chemistry carries 25 one-mark questions covering the diploma syllabus: atomic structure and periodic properties, chemical bonding, volumetric analysis, acids–bases and pH, electrochemistry and corrosion, water treatment and hardness, fuels and combustion, and polymers and alloys.
Core rules
- Equivalent weight = molecular weight ÷ n-factor; normality = gram equivalents per litre; N = M × n-factor. For Na₂CO₃ the n-factor is 2, so its equivalent weight is 53.
- pH = −log[H⁺]; for a strong monobasic acid, pH = −log C; pH + pOH = 14 at 25 °C.
- Hardness is reported as mg/L (ppm) of CaCO₃ equivalent. Temporary hardness (bicarbonates) is removed by boiling; permanent hardness (sulphates, chlorides) by ion exchange or lime–soda.
- Electrochemistry: oxidation at the anode, reduction at the cathode; EMF = E°cathode − E°anode; rusting is an electrochemical cell with iron as the anode.
Worked example
4.0 g of NaOH (molar mass 40) is dissolved to make 250 mL of solution. Moles = 4.0/40 = 0.10 mol, so molarity = 0.10/0.250 = 0.40 M. NaOH has an n-factor of 1, so normality is also 0.40 N. By contrast, a 0.40 N H₂SO₄ solution is only 0.20 M because its n-factor is 2 - exactly the kind of conversion the paper tests.
Traps that cost marks
- Treating molarity and normality as equal for H₂SO₄, Na₂CO₃ or Ca(OH)₂.
- Forgetting that molarity changes with temperature while molality does not.
- Quoting hardness in mg/L without converting the actual salt mass to CaCO₃ equivalents.
- Reversing anode and cathode when describing a corrosion cell.
- Ignoring that pH 7 indicates neutrality only at 25 °C.