Grade 12 chemistry has six units: electronic structure, periodic properties and bonding, acids and bases, thermodynamics and reaction rates, organic chemistry, and electrochemical cells. The calculation and reasoning questions follow a few patterns. These are original practice examples on topics from the book.
Example 1: conjugate acid-base pairs
In HCl + H₂O → H₃O⁺ + Cl⁻, HCl donates a proton (acid) and H₂O accepts it (base). The conjugate pairs are HCl / Cl⁻ and H₃O⁺ / H₂O. Rule: the two members of a pair differ by exactly one H⁺.
Example 2: pH
A solution has [H₃O⁺] = 1 × 10⁻³ M. pH = −log[H₃O⁺] = 3. If the concentration falls to 1 × 10⁻⁵ M, the pH rises to 5: a less acidic solution has a higher pH.
Common mistake: thinking a larger pH means more acid. Each step of 1 in pH is a tenfold change in [H₃O⁺].
Example 3: cell potential
A galvanic cell is made from Zn²⁺/Zn (E° = −0.76 V) and Cu²⁺/Cu (E° = +0.34 V). The electrode with the higher reduction potential, copper, is the cathode; zinc is the anode and is oxidised. E°cell = E°cathode − E°anode = 0.34 − (−0.76) = 1.10 V. A positive E°cell means the cell works spontaneously, and electrons flow from zinc to copper through the wire.
Common mistake: subtracting in the wrong order, or flipping the sign of a potential and then subtracting it again.
In cells, decide the cathode first (higher reduction potential). Everything else (anode, electron direction, E°cell) follows from it.
How EXAMEV helps
The EXAMEV grade 12 chemistry bank has 1,388 questions across all six units, from electron configuration and the periodic table to organic naming and galvanic cells, with explanations. The examples here are EXAMEV practice.