Common mistake: Using mL directly in c = n/V

Using mL directly in c = n/V — always convert to litres first: 1 mL = 0.001 L

Common mistake: Ignoring stoichiometry

Ignoring stoichiometry — not all acids and bases react in a 1:1 ratio; check the equation first

Common mistake: Using a rough titre instead of the concordant average

Using a rough titre instead of the concordant average — this loses marks on procedure questions

Common mistake: Calculating pH from pOH without subtracting from 14

Calculating pH from pOH without subtracting from 14 — or forgetting that pH + pOH = 14 only at 25°C

VCE Units 1–4 · Chemistry

VCE Chemistry — Chemical Analysis

Chemical analysis covers the techniques used to identify and quantify substances — from acid-base titration calculations through to spectroscopic methods. In VCE, titration calculations appear in almost every exam and SAC. Knowing how to work from titre volume to moles to concentration, and how to interpret spectra, are the two essential skills.

Key Concepts & Formulas

Concentration: c = n/V (mol/L); moles: n = cV (when V is in litres)
Titration calculation: n = cV for the standard solution; use stoichiometry to find moles of analyte
Always use the average titre (concordant results) — discard any that differ by more than 0.1 mL
pH = −log₁₀[H⁺]; pOH = −log₁₀[OH⁻]; pH + pOH = 14 at 25°C
Strong acid: fully dissociates — [H⁺] = concentration of acid
Strong base: fully dissociates — [OH⁻] = concentration × number of OH⁻ per formula unit
Buffer solution: resists pH change when small amounts of acid or base are added; contains weak acid + conjugate base
Chromatography: separates mixtures based on different affinities for stationary vs mobile phase
Rf value = distance moved by substance / distance moved by solvent front
Mass spectrometry: molecular ion peak (M⁺) gives molar mass; fragmentation pattern identifies structure

Practice Questions

4 questions

Attempt each question before reading the hint. These are styled to match VCE exam format.

Q1.25.0 mL of NaOH solution is titrated against 0.100 mol/L HCl. The average titre is 22.4 mL. Find the concentration of the NaOH solution.

3 marks

Q2.Find the pH of (a) 0.050 mol/L HCl and (b) 0.020 mol/L NaOH at 25°C.

3 marks

Q3.A student performs a titration using oxalic acid (H₂C₂O₄) as the primary standard and NaOH as the titrant. The equation is H₂C₂O₄ + 2NaOH → Na₂C₂O₄ + 2H₂O. If 0.210 g of oxalic acid (M = 90.0 g/mol) is dissolved and titrated with 28.0 mL of NaOH, find the concentration of NaOH.

4 marks

Q4.A compound shows an Rf value of 0.45 in TLC. The solvent front moved 12.0 cm. How far did the compound travel?

1 mark

Common Mistakes to Avoid

These are the errors that VCE students most frequently make in Chemical Analysis — and that examiners are specifically watching for.

Using mL directly in c = n/V — always convert to litres first: 1 mL = 0.001 L
Ignoring stoichiometry — not all acids and bases react in a 1:1 ratio; check the equation first
Using a rough titre instead of the concordant average — this loses marks on procedure questions
Calculating pH from pOH without subtracting from 14 — or forgetting that pH + pOH = 14 only at 25°C

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