A sticking point is the smallest piece of a question you cannot yet justify. Finding it is itself a skill, and it makes any help, from a teacher, a book or your own revision, much faster. The aim here is a short written note that someone else could act on without asking you ten questions.
This is the last lesson of the extended explanation and error repair module, and it draws on the four before it: ratio, explanation, equation and reasoning chain.
What makes a sticking point “exact”?
A topic-sized statement cannot be repaired in an hour. A line-sized statement can.
| Too big | Exact |
|---|---|
| “I can’t do moles.” | “In 2Al + 6HCl → 2AlCl₃ + 3H₂ I can find moles of Al, but I don’t see why H₂ is 1.5 times that.” |
| “I don’t get rates.” | “I can say faster collisions, but I don’t know why a catalyst changes the rate when the temperature has not changed.” |
| “Equations are hard.” | “I balance the metal first, then the oxygen changes, and I don’t know what order to use.” |
The five-line template
Write these five lines for each question you are stuck on.
- The question (or its number and source).
- My last sure line: the last step I can fully justify.
- My first unsure line: what I wrote or wanted to write next.
- What I expected, and what I got (or what confused me).
- One guess at why, even if you think it is wrong.
The guess matters. A wrong guess shows exactly which idea needs repair.
Worked example
All data are invented for practice. Question: 2.4 g of magnesium reacts with excess hydrochloric acid, Mg + 2HCl → MgCl₂ + H₂. Find the moles of hydrogen.
- Question: moles of H₂ from 2.4 g Mg.
- Last sure line: moles of Mg = 2.4 ÷ 24 = 0.10 mol.
- First unsure line: I wrote moles of H₂ = 0.10 × 2 = 0.20 mol.
- Expected vs got: I expected 0.20 because the equation shows a 2 in front of HCl. The answer book says 0.10.
- My guess: I used the coefficient of HCl instead of the coefficient of H₂.
This is a five-line note that points to one idea: read the coefficients of the two substances you are linking, here Mg and H₂, both 1. The answer is 0.10 mol.
The mistake to watch for
Vague note: “Got the wrong answer, don’t understand the ratio.”
This leaves the helper to guess which ratio, which step and which idea. The note gives no information that a blank page would not.
The correction is to name the two substances, the ratio you used, the ratio you expected, and where the difference came from. If you cannot name the ratio, that itself is the sticking point.
Check yourself
Rewrite each vague statement as an exact sticking point.
1. “I don’t understand balancing.”
Show answer
Any version that names the equation and the step is acceptable, for example: “In Al + O₂ → Al₂O₃ I balance Al first, then oxygen becomes 3 on the left and 2 on the right, and I don’t know how to get both to the same even number.”
2. “I lose marks on explain questions.”
Show answer
For example: “On ‘explain why a powder reacts faster’ I write ‘it has more surface area’ and stop. I don’t know what to add about particles to earn the second mark.”
3. “My conclusion is always wrong.”
Show answer
For example: “When a solid displaces copper from solution, I write which metal it is, but the mark scheme says I can only say it is more reactive. I don’t know how to decide how far I can go.”
Where this leads next
Bring your notes to the mixed practice set, and log each error in the mistake log and retest queue. If the sticking point is a ratio, try the mole and equation-ratio tutor; for equations, use the equation balance reasoning trainer.
A written sticking point is what a teacher in online one-to-one Chemistry tuition can work from straight away, so the first hour goes on the repair.