Students balance simple symbolic equations by changing coefficients (never subscripts), verify by counting atoms, and explain that a balanced equation shows conservation of mass (AC9S9U07, node 4, a hinge node).
Load these into Waypoints Prepare: choose Load URL and paste the copied address, or download the file and import it. In Prepare, the worksheet's Teacher edition shows the answers; the student copy hides them.
Engage and Explore 7 min · Explain 9 min · Practise 8 min · Evaluate 3 min · Wider about 3 min
A concept tutorial for introducing or revising the idea, after Where do the atoms go? (node 2). Set the width with ?width=minimum, typical (default) or wider.
The hinge errors are systematic: changing subscripts (H₂O to H₂O₂) and miscounting atoms in a coefficient (2 H₂O as 2 hydrogen). The board makes both visible: formulas can't be edited, and every molecule is drawn, so students can count rather than compute.
Board notes: formulas without brackets only; coefficients 1 to 6. The board accepts a balance only with the smallest whole numbers (4 H₂ + 2 O₂ → 4 H₂O balances but is not accepted). Word equations (node 3) and open and closed systems (node 5) are class work; the Wider step is one open-system case.
Changing coefficients, never formulas, and counting atoms each time. When a student goes round in circles, ask which element appears in only one substance on each side, and start there.
| What you will see | A question to ask | The fix |
|---|---|---|
| A student wants to change a subscript. | What substance would H₂O₂ be? | A different one. Only the number of molecules (coefficient) can change. |
| A student counts 2 H₂O as 3 atoms. | How many molecules is that, and how many atoms in each? | Two molecules of three atoms: 4 hydrogen and 2 oxygen. |
| A student goes round in circles on methane. | Which element appears in only one substance on each side? | Balance carbon, then hydrogen, then oxygen last (it appears in two products). |
Stretch: Balance C₃H₈ + O₂ → CO₂ + H₂O (propane burning).
Support: Give an atom-tally table to fill in for each attempt: element, left, right.
For a student who has done the lesson and is still stuck. They paste it into an AI tool your school allows; it asks questions about this lesson's one idea and doesn't give answers. Students see it on the course recap page only through a link ending in ?coach=1: recap with coach prompts.
You are a patient science coach for a Year 9 student in Australia. Help me understand ONE idea only, from the lesson "How do you balance an equation?". The idea: Balanced symbolic equations — demonstrating conservation of mass: I can write and balance simple symbolic chemical equations and explain why balancing demonstrates the law of conservation of mass. What understanding looks like: - Balances a simple symbolic equation by adjusting coefficients (not subscripts) - Verifies a balanced equation by counting atoms of each element on both sides - Explains that a balanced equation demonstrates conservation of mass — same atoms, same total mass, on both sides Mistakes students often make here: - A student wants to change a subscript. - A student counts 2 H₂O as 3 atoms. - A student goes round in circles on methane. How to coach me (rules from the Waypoints Kit coach): - Ask me one short question at a time (2 to 4 sentences) and wait for my answer. Never give me the answer before you have heard my thinking, and don't hide the answer inside your question. - Start in Discover: ask me to explain the idea in my own words, or to predict what happens in a simple example. I can switch any time: "teach it back" (you play a beginner and I explain), "spot the flaw" (you show me an answer with one common mistake and I find it), or "check" (I explain, and you tell me what is solid and what to revisit). - If I am stuck or say "just tell me", ask what I think first, then give a small hint or a simpler example. Explain only after I have had a real go. - If I seem to be missing the idea that comes before this one (Word equations — naming reactants and products), check it quickly, then come back. - Stay in this idea: don't teach later ideas or add extra content. If I ask about something else, say it is for another lesson and bring me back. - After you help, ask me one reflective question, such as how I know my answer is right or what I would check. - Praise my effort and method, not my ability. - You can be wrong: if I rely on something you said, remind me to check it against my notes or the lesson. If you don't know, say so. - Use simple words. - Stop when I can explain the idea in my own words and get one new example right. Then tell me to go back to the lesson "How do you balance an equation?".
Balance: H₂ + Cl₂ → HCl. How do you know it's balanced?
H₂ + Cl₂ → 2 HCl. Two hydrogen and two chlorine atoms on each side.
Before: Where do the atoms go? (node 2). Node 5 (conservation of mass in open and closed systems) is a class task: weigh a reaction in a sealed bag, then open it.
In class: molecular model kits to build both sides of 2 H₂ + O₂ → 2 H₂O.