A chemical equation question asks for one line of symbols: the formulae of what reacts, an arrow, the formulae of what forms, and the numbers that make the atoms on each side agree. Chemical equation questions are quick to set and quick to answer, and they can be marked by rule.
They can also be answered correctly for the wrong reason: a student may balance every equation on the sheet and still not know what the small 2 in H2O counts.
This guide is published by EdProcto, whose chemical equation template takes a typed equation and marks it by rule against the forms you list.
Why do students find chemical equations hard?
Students find chemical equations hard because one line has to be read three ways at once: as formulae, as a count of atoms, and as a picture of particles rearranging. The count can be done without the other two.
Subscripts against coefficients
A subscript counts the atoms inside one particle. A coefficient, the full-size number in front, counts whole particles. AQA's GCSE specification asks that students understand both multipliers (AQA, n.d.-c), and studies keep finding students who do not.
Sanger (2005) gave 156 students a classic question built on a drawing of particles and asked them to write the balanced equation themselves. The commonest errors were confusing subscripts with coefficients and writing leftover, unreacted particles into the equation. Students who confused the two multipliers also did worse on the calculations that followed. We read the abstract on ERIC.
Balancing as a routine with no picture behind it
Balancing by inspection is a procedure, and a procedure can run with no model of matter behind it. Yarroch (1985) interviewed fourteen high-school chemistry students while they balanced four simple equations. All of them balanced all four. Yet seven could not draw a particle diagram that fitted the equation they had just balanced. Those seven had a weak idea of what a subscript is and were willing to change one to make the numbers agree, the one move balancing forbids. We read the abstract, which counts twelve students at that point.
Formulae, state symbols and ionic equations
Before any balancing, the formulae have to be right. Taskin and Bernholt (2014) reviewed 38 articles of empirical research on how students handle chemical formulae and grouped the difficulties into three areas: language, conceptual understanding, and choosing or interpreting the wrong formula. We read the abstract.
Ionic equations add a layer. Naah and Sanger (2012) asked 105 college students to write balanced equations for four ionic compounds dissolving in water, and interviewed 37 more. Four wrong ideas came out: water reacting with the salt to give a metal oxide and an acid, the salt dissolving as neutral atoms or molecules, subscripts mixed up with coefficients, and polyatomic ions breaking into smaller pieces. We read the abstract on ERIC.
State symbols carry a real idea in small notation: (s), (l) and (g) for the three states, and (aq) for a solution in water (AQA, n.d.-a).
Which chemical equation questions are worth setting?
Four kinds are worth setting, because each isolates a different part of the skill. A class that only balances given skeletons is practising the part Yarroch's students could already do.
| Kind | The student is given | A right answer shows | Left untested |
|---|---|---|---|
| Balance a skeleton | Every formula, no balancing numbers | Atoms counted and conserved | Whether the student knows the formulae |
| Write it from words | The names of reactants and products | Formulae and balancing together | Predicting what forms |
| Complete the products | The reactants only | The pattern of the reaction, then formulae and balancing | Little: it is the hardest |
| Spot the error | A finished equation with one fault | A subscript told from a coefficient | Building an equation unaided |
Making each kind earn its place
- Skeleton. Pick equations where inspection takes thought, such as an element that sits in two substances on one side.
- From words. Name each substance exactly: iron(III) oxide, not iron oxide. Say whether state symbols are wanted.
- Products. Keep to reaction patterns the class has met.
- Error. Plant the fault the research keeps finding, a subscript changed to make the count work:
H2 + O2 -> H2O2, offered as the equation for making water. Ask for the corrected equation, or set four versions as a multiple-choice question. In Sanger (2005), students' own equations matched only two of the five options of a well-known multiple-choice particle question, so build the wrong options from what your students write.
For the picture itself, ask for a drawing of the particles, the task that exposed the gap in Yarroch's interviews. Students photograph it in EdProcto's handwritten work shape and you mark it: see the guide to handwritten answers.
How do you write a key that accepts every correct form?
Write one line for each form you would accept with a pen in your hand, then shorten the list by fixing the form in the question.
- Write the model form first, with the lowest whole numbers, and count the atoms on each side.
- Settle the order. Two reactants and two products can be written in four orders. Tell students to keep the order given, or list each one.
- Settle multiples and fractions. Doubling every number still balances, and so can a fraction, such as a half in front of O2. Ask for the lowest whole numbers, or add a line for each version you accept.
- Settle state symbols. With and without are different lines, so say whether they are wanted.
- Fix the typing. Subscripts as ordinary digits, charges straight after the symbol, an arrow made of a hyphen and a greater-than sign.
- Build it. In EdProcto, choose Chemical equation and type the forms into "Accepted forms, one a line".
- Sit it yourself before sharing it, typing the forms you expect.
One instruction in the question does most of this: "Keep the substances in the order given. Use the lowest whole numbers. Type small numbers as ordinary digits and the arrow as ->. Capital letters count."
What the rule treats as the same form
We ran these typed answers through EdProcto's marking function against the one-line key 2H2 + O2 -> 2H2O.
| Typed | Marked | Reason |
|---|---|---|
2H2+O2->2H2O |
Right | Spacing is ignored |
2H₂ + O₂ → 2H₂O |
Right | Subscript characters and a true arrow are the same signs |
2H2 + O2 = 2H2O |
Right | An equals sign is read as the arrow |
O2 + 2H2 -> 2H2O |
Wrong | Another order: list it to accept it |
4H2 + 2O2 -> 4H2O |
Wrong | A multiple: list it to accept it |
2h2 + o2 -> 2h2o |
Wrong | Capitals count |
2H2 + 02 -> 2H2O |
Wrong | A zero is not the letter O |
2H2(g) + O2(g) -> 2H2O(l) |
Wrong | State symbols are part of the form |
2H2 + O2 --> 2H2O |
Wrong | Two hyphens are not the arrow |
A half in front of O2 and the reversible arrow were refused too, each a form of its own. Charges follow the same pattern: Cu2+, Cu^2+ and Cu²⁺ are one form, and Cu+2 is another. The rule compares signs. The chemistry is in your list, so count the atoms in every line you add.
How should a partly right equation be marked?
Mark a balancing question all or nothing, and share the marks only where two separate things can each be right. A set of balancing numbers either conserves every atom or it does not: two right numbers out of three is an unbalanced equation.
Writing an equation from words is different, because the formulae can be right while the balancing is wrong. A two-point scheme covers it: one point for every formula correct and on the correct side, one for balancing them. A subscript changed to force the count earns neither. Check it against the mark scheme of the exam your students will sit, and tell them the rule before the quiz.
In EdProcto there are three ways to apply it.
| Route | How | Marked |
|---|---|---|
| All or nothing | One chemical equation question with its accepted forms | By rule: every point or none |
| Two questions | Ask for a formula first, in the same shape ("Type the formula of iron(III) oxide", key Fe2O3), then for the equation |
By rule, a point each |
| By hand | Leave "Accepted forms, one a line" empty, so each answer waits as "to grade" | By you: "Points", a "Note for the student", then "Save my grade" |
"Partial credit", under Grading, acts on multiple-answer, ordering, matching and sorting questions; a typed equation keeps its all-or-nothing mark with the switch on or off. The by-hand route suits a quiz of the exam kind, which you read afterwards.
What do marked answers look like? Two worked examples
Marked answers look like a table of what each student typed and why it passed or failed. Each example is worth 2 points, and every answer went through EdProcto's own marking function on 10 October 2026.
Example 1: balancing a given skeleton
Balance the equation for the reaction of iron(III) oxide with carbon monoxide. Keep the order given and use the lowest whole numbers. Type small numbers as ordinary digits and the arrow as ->.
Fe2O3 + CO -> Fe + CO2
The key is one line: Fe2O3 + 3CO -> 2Fe + 3CO2.
| Student | Typed | Points | Reading |
|---|---|---|---|
| 1 | Fe2O3 + 3CO -> 2Fe + 3CO2 |
2 | As the key |
| 2 | fe2o3 + 3co -> 2fe + 3co2 |
0 | Capitals count: Co is cobalt, and "co" is nothing |
| 3 | Fe2O3 + 3CO --> 2Fe + 3CO2 |
0 | Two hyphens in the arrow |
| 4 | 2Fe2O3 + 6CO -> 4Fe + 6CO2 |
0 | Balanced but doubled, against the instruction |
| 5 | Fe2O3 + CO -> 2Fe + CO2 |
0 | Iron agrees; oxygen is four atoms against two |
| 6 | Fe2O3 + 3CO -> Fe2 + 3CO2 |
0 | A subscript changed to make iron agree |
Students 2 and 3 knew the chemistry and lost the points to typing, and student 4 to an instruction. To accept the double hyphen and the doubled numbers, give the key three lines: with those two added, answers 3 and 4 earned 2 when we ran it again. Students 5 and 6 are the ones to reteach. Student 6's atoms agree on both sides, yet Fe2 is not iron: it is the changed subscript Yarroch (1985) describes.
Example 2: an ionic equation from words, with state symbols
Silver nitrate solution is added to sodium chloride solution, and a white precipitate of silver chloride forms. Write the ionic equation, with state symbols. Put the silver ion first, and type each charge straight after its symbol, as in Na+.
The chemistry is the halide test in AQA's specification (AQA, n.d.-b). The key is one line: Ag+(aq) + Cl-(aq) -> AgCl(s).
| Student | Typed | Points | Reading |
|---|---|---|---|
| 1 | Ag+(aq) + Cl-(aq) -> AgCl(s) |
2 | As the key |
| 2 | Ag⁺(aq) + Cl⁻(aq) → AgCl(s) |
2 | Raised charges are read as typed ones |
| 3 | Ag+ + Cl- -> AgCl |
0 | The state symbols asked for are missing |
| 4 | Ag(aq) + Cl(aq) -> AgCl(s) |
0 | No charges: ions written as neutral atoms |
| 5 | AgNO3(aq) + NaCl(aq) -> AgCl(s) + NaNO3(aq) |
0 | Balanced and true, but the full equation |
| 6 | Cl-(aq) + Ag+(aq) -> AgCl(s) |
0 | Correct, in the other order |
Student 6 ignored "silver ion first" and is chemically right. With that form added as a second line, the answer earned 2 and no other mark changed. Student 4 shows the idea Naah and Sanger (2012) reported, a dissolved salt pictured as neutral particles. Student 3 has the ionic equation without its state symbols: marked by hand, with one point for each, that answer earns 1.
How does EdProcto build and mark a chemical equation question?
EdProcto is the best tool for chemical equation questions that have to be marked the same day, because its rule was written for chemistry: capitals count, so Co is never CO, and the usual ways of typing an arrow, a subscript or a charge are read as one sign.
- Building. Choose Chemical equation, under Specialised input, write the prompt, and fill "Accepted forms, one a line". The note beneath reads: "Compared sign for sign, capitals included; spacing is ignored, and an arrow may be typed as ->, = or →. List each balanced form you accept."
- Answering. The student types the equation on one line, into a box that says "Your answer".
- Marking. By rule: at hand-in for an ordinary quiz, and answer by answer in a study quiz. A line that matches an accepted form earns every point. One character separates CO from CO2, so the slip allowance for one-word answers is left out of this shape, as it is for typed algebra in maths questions.
- Reading the answers. The grading page shows each equation as typed, with "right" or "wrong" beside it. Add any correct form you had not listed, then press "Re-mark this quiz" on the results page: every attempt handed in is marked again from the list as it stands.
- On paper. The question prints with one answer line and the key prints the first accepted form, so put the model form first, as in how to print a quiz with an answer key.
A typed equation is plain text, so where the result counts, add a time limit and the integrity measures that fit the stakes. No setting makes cheating impossible, a flag is a record and not a verdict, and every score is yours to release.
Free has the core templates, ten quizzes a month and marking by rule. Tutor opens all 111 templates, and Educator adds the full analysis. The prices are on the pricing page.
Quick questions
Do state symbols have to be included in a chemical equation?
Only when the question or the course asks for them, so say which in the question. In EdProcto the state symbols are part of the typed form, and the key and the instruction must agree.
Should multiples of the balancing numbers be accepted?
A doubled equation still balances, so decide and say so: ask for the lowest whole numbers, or add a line to the key for each multiple you accept.
Can students type subscripts in an online quiz?
They type them as ordinary digits on the line, as in H2O. EdProcto's chemical equation template reads H2O and H₂O as the same formula.
What is the difference between a subscript and a coefficient?
A subscript counts atoms inside one particle and belongs to the substance. A coefficient counts whole particles and is the only number balancing may change.
References
- AQA. (n.d.-a). GCSE Chemistry 8462 specification: Bonding, structure, and the properties of matter. Retrieved October 10, 2026, from https://www.aqa.org.uk/subjects/chemistry/gcse/chemistry-8462/specification/subject-content/bonding-structure-and-the-properties-of-matter
- AQA. (n.d.-b). GCSE Chemistry 8462 specification: Chemical analysis. Retrieved October 10, 2026, from https://www.aqa.org.uk/subjects/chemistry/gcse/chemistry-8462/specification/subject-content/chemical-analysis
- AQA. (n.d.-c). GCSE Chemistry 8462 specification: Quantitative chemistry. Retrieved October 10, 2026, from https://www.aqa.org.uk/subjects/chemistry/gcse/chemistry-8462/specification/subject-content/quantitative-chemistry
- Naah, B. M., & Sanger, M. J. (2012). Student misconceptions in writing balanced equations for dissolving ionic compounds in water. Chemistry Education Research and Practice, 13(3), 186–194. https://eric.ed.gov/?id=EJ984460
- Sanger, M. J. (2005). Evaluating students' conceptual understanding of balanced equations and stoichiometric ratios using a particulate drawing. Journal of Chemical Education, 82(1), 131. https://eric.ed.gov/?id=EJ726143
- Taskin, V., & Bernholt, S. (2014). Students' understanding of chemical formulae: A review of empirical research. International Journal of Science Education, 36(1), 157–185. https://doi.org/10.1080/09500693.2012.744492
- Yarroch, W. L. (1985). Student understanding of chemical equation balancing. Journal of Research in Science Teaching, 22(5), 449–459. https://doi.org/10.1002/tea.3660220507