The short answer
The acid-base reasoning that turns up again and again in Section III chemistry.
Written and checked by GAMSAT tutors — not AI-generated.
Try the reasoning style
We treat forgetting as a failure — a lapse to be patched with reminders and records. Yet a mind that kept everything could not think; it would drown in the undifferentiated noise of every moment it had ever lived. To forget is not so much to lose information as to decide, mostly without our noticing, what was never worth keeping.
The author's argument relies most directly on which unstated assumption?
Pick an option to see how the tutor reasons to the answer — not just whether you were right.
Not quite — the answer is B.
Work backwards from the conclusion: a mind that ‘kept everything’ supposedly ‘could not think.’ That only follows if thinking means leaving most of experience out — so B is the premise the argument quietly rests on. A raises reliability, which the passage never weighs; C contradicts ‘mostly without our noticing’; D smuggles in a claim about intellect the passage never makes. The question rewards finding the hidden premise, not recalling a fact.
Acid–base chemistry is a Section III staple. You don't need to memorise pKa tables — you need to reason fluently with a few core ideas.
The definitions everything else rests on
Acid and base
An acid donates a proton (H⁺); a base accepts one. That is Brønsted–Lowry, and it is the definition GAMSAT questions are built on.
Conjugate pairs
What is left after an acid loses its H⁺ is its conjugate base; a base that gains an H⁺ becomes its conjugate acid. They always come in pairs, and the pair is a see-saw — the stronger one end, the weaker the other.
Strong versus weak
Strong acids and bases dissociate completely. Weak ones dissociate only partially, which means a weak acid in water is an equilibrium — so everything you know about equilibrium applies here too.
pH in one line
pH = −log[H⁺], so each whole pH unit is a 10-fold change in [H⁺]. pH 3 is ten times more acidic than pH 4 — and a hundred times more than pH 5.
Common trap: treating a 2-unit pH change as "twice as acidic". It is actually 100×. The log scale is exactly where questions catch people.
Reading any titration curve
Find the steep vertical jump
That is the equivalence point — moles of base ≈ moles of acid.
Look at the flat region before it
That is the buffer zone, where pH resists change.
Go halfway to equivalence
At the half-equivalence point, pH ≈ pKa of the acid.
Why a buffer resists
A buffer holds a weak acid and its conjugate base at the same time. Add H⁺ and the base mops it up; add OH⁻ and the acid neutralises it. It works best when the two are roughly equal — which is around the pKa, and which is exactly the flat stretch on the curve above. Blood and the inside of a cell run on this, which is why GAMSAT keeps coming back to it.
Worked example
Acid A has pKa 3.2; acid B has pKa 5.6. Which is the stronger acid — and which has the stronger conjugate base?
Check yourself
On the titration curve above, what is happening in the flat region before the steep jump?
Key takeaways
- pH = −log[H⁺]: every unit is a 10× change in acidity.
- Stronger acid = lower pKa = more dissociation = weaker conjugate base.
- Titration curve: steep jump = equivalence point, flat zone = buffer, half-way = pKa.
- Reason from these and you can handle acids you have never met.
Practise this with real GAMSAT-style questions
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