Scientific writing is not fancy writing. It is writing that cannot be misunderstood, by a reader who was not in the room and who is looking for the weak spot.
Chemistry adds a second requirement on top of that one. This subject uses ordinary English words with narrower meanings than they have outside it, and it writes substances in a notation where one character changes what you are talking about. Getting those right is not politeness. It is the difference between being read correctly and being read.
Say what you measured, not what you felt
❌ The reaction went really fast and got super hot.
✅ The temperature rose from 21.0 °C to 47.5 °C in 30 s.
Adjectives are the reader’s job. Give them the number and let them decide whether it was fast.
Keep observation and interpretation in separate sentences
An observation is what an instrument or your senses recorded. An interpretation is what you think it means. Mixing them is how a shaky inference gets smuggled in as a fact.
Observation: A white solid formed immediately on mixing, and the mixture remained cloudy after five minutes of standing.
Interpretation: A precipitate has formed, which suggests one of the possible products is insoluble under these conditions.
Note what the observation does not say. It does not say “a precipitate formed” — that word already contains the interpretation. You saw a white solid.
Claim what your data supports, and no more
| Too strong | Honest |
|---|---|
| This proves the compound is ionic. | The solution conducted at 1180 µS/cm against a 2 µS/cm blank, which supports the compound being ionic. |
| The results were wrong. | The recovered mass was 12% below the calculated value; product left on the filter paper accounts for at least part of that. |
| The two yields were the same. | The two yields differ by less than the ±2 percentage points our balance precision allows, so the data cannot distinguish them. |
| The unknown was an acid. | The unknown turned blue litmus red and neutralised a known base, which is consistent with an acid; a pH measurement would confirm it. |
"Prove" is not a science word
Evidence supports, is consistent with, or fails to support. One lab period proves nothing at all, and a reader who sees “proves” in your first paragraph trusts everything after it a little less. This is the single easiest mark in the course to keep.
The words this subject uses precisely
Each of these pairs is used loosely in ordinary speech and precisely here. Mixing them up will cost you marks and, worse, will make sentences that are simply not decodable.
| Pair | The distinction |
|---|---|
| Amount and mass | In chemistry, amount means a number of moles. A mass is in grams. “A large amount” and “a large mass” are different claims |
| Concentrated and strong | Concentrated is how much solute per litre. Strong is how completely a substance ionises in water. A dilute solution of a strong acid is perfectly ordinary, and so is a concentrated solution of a weak one |
| Dilute and weak | The same distinction, from the other end. These two are the most commonly swapped words in the whole course |
| Molecule and formula unit | Sodium chloride has no molecules — it is a lattice, and names the ratio. Water does have molecules |
| Solution, solvent, solute | The solute dissolves, the solvent does the dissolving, and the solution is both together |
| Reactant and reagent | A reactant is consumed in the equation. A reagent is anything you add — which may be a catalyst, an indicator, or a solvent |
And one question to ask yourself every time you write the word mole: a mole of what? A mole of oxygen atoms and a mole of oxygen molecules differ by a factor of two, and the sentence usually does not say which you meant. Write it out. See The Mole.
Write chemistry so it can be read
Formulas need their subscripts and charges to mean anything. is water; H2O is a typing accident that happens to be readable. Reactions get a proper arrow, states get their brackets, and ions get their charges:
Sulfate is , not SO4-2. The charge sits after the subscript, and the number comes before the sign. Getting this right is not fussiness — and are different substances and the difference is one character. The full list is in Polyatomic Ions.
Three more conventions that carry meaning:
- States are not optional in this course.
(aq)and(s)are the whole content of a precipitation equation — without them, Precipitation and Net Ionic Equations says nothing. - Coefficients go in front, subscripts stay put. is two water molecules; is not a substance. Changing a subscript to balance an equation changes what reacted.
- Capitals matter. Co is cobalt; CO is carbon monoxide.
Units and digits are part of the claim
A number without a unit is not an answer. 4.2 what — grams, moles, millilitres, degrees? And a unit without a number is a category, not a measurement.
The digits matter in the same way. Writing 0.0787132 mol when your balance gave you two significant figures is a claim about your equipment, and it is a false one. Writing 0.08 mol when the balance gave you four is throwing away something you paid for. Both are marked as claims, because both are claims — Significant Figures in Practice has the reasoning.
Passive voice is fine here
“The solution was heated to 40 °C” keeps the reader’s attention on the procedure rather than on who was holding the beaker. Method sections are one of the few kinds of writing where that is the right choice, so ignore anybody who tells you to purge it.
Conclusions are different. “We recovered 1.31 g” is clearer than “1.31 g was recovered”, because in a conclusion it matters that a person made a judgement, and hiding the person hides the judgement.
More on structure: Writing a Lab Report. More on the words that give away an overclaim: Reading a Data Table and What Counts as Evidence.