Weighed Before, Weighed After
A 60-minute Grade 5 lesson on measuring and graphing to show that the total weight of matter is conserved through a change.
Weighed Before, Weighed After is a free 60-minute Grade 5 science lesson plan for Common Core standard 5-PS1-2 — measure and graph to show that weight is conserved when matter changes. It is timed across 5 sections, gives the exact wording to use where the wording carries the mathematics, names 3 misconceptions with the teaching move that addresses each, and ends with an exit ticket and a printable worksheet with its answer key.
- Grade:
- Grade 5
- Length:
- 60 minutes
- Standard:
- 5-PS1-2
Grade 5 · Physical Science
5-PS1-2
Measure and graph quantities to provide evidence that regardless of the type of change that occurs when heating, cooling, or mixing substances, the total weight of matter is conserved.
Objective
Students will be able to measure mass before and after a change and account for any difference.
Students are successful when they can
- Measures on the same balance both times.
- Seals the container where gas is produced.
- Explains a loss rather than accepting it.
What you need
- Balance, sealable jars and bags, vinegar, baking soda, ice, sugar
- Graph paper for mass-before against mass-after
- The printable practice sheet linked at the end of this plan
The lesson
Warm-up
5 min- Fizz vinegar and soda in an open beaker on a balance and watch the mass fall.
- Ask whether matter has just been destroyed.
Teach — seal it, then ask again
15 min- Repeat the same reaction in a sealed jar. The mass does not move.
- Ask what the difference between the two runs was. Only whether gas could escape.
- Do sugar dissolving and ice melting, sealed: unchanged both times.
- Plot mass-before against mass-after for all four and look at the line.
- State the claim: total mass is conserved when nothing can leave.
- Say why the open jar is still useful: it shows what the escaping matter was doing.
“Did anything leave? If so, it left the jar, not the world.”
Investigate — four changes, sealed and open
22 min- Groups measure mass before and after four changes on the same balance.
- They repeat the gas-producing one both sealed and open.
- They graph before against after for all readings.
- They write an explanation for the one point that does not sit on the line.
Independent practice
15 min- Students complete the 'Weighed Before, Weighed After' page.
- Check the open-jar loss is explained rather than ignored.
Close
3 min- Ask what would have to be true for matter genuinely to be destroyed.
What goes wrong, and why
Each of these is a reasoning error rather than carelessness. The fix addresses the reasoning.
Concludes matter is destroyed from the open jar.
Why: The balance says less.
Fix: Seal it and repeat. The matter left the jar, not existence.
Uses a different balance for the second reading.
Why: Any balance measures mass.
Fix: Two balances can disagree by more than the change. Use one.
Thinks dissolving reduces mass.
Why: The solid vanishes.
Fix: Weigh the sealed beaker. Unchanged.
If they are not there yet
- Two changes rather than four.
- A graph with the axes drawn and one point plotted.
If they finish early
- Design a way to catch and weigh the escaping gas.
- Predict the mass after a change you have not tried.
- Explain a rusting nail gaining mass.
Exit ticket
An open jar of vinegar and soda loses 3.5 g; a sealed one loses none. What does that show?
What to look for: Matter is conserved; the gas escaped from the open jar rather than being destroyed. Concluding destruction means the sealed comparison needs another run.
Printable practice for 5-PS1-2
Free to print and copy, answer key included. Each sheet can generate a fresh set of problems for a retake.
- Weighed Before, Weighed AfterRead the record, then answer the questions.
Questions about Weighed Before, Weighed After
How long does the Weighed Before, Weighed After lesson take?
60 minutes, split across 5 timed sections: warm-up 5 min, teach 15 min, investigate 22 min, independent practice 15 min, close 3 min. The minutes are stated per section and add up to the stated length, so the plan can be cut or extended at a section boundary rather than abandoned halfway.
Which standard does Weighed Before, Weighed After teach?
5-PS1-2 — 5-PS1-2, Physical Science for Grade 5: “Measure and graph quantities to provide evidence that regardless of the type of change that occurs when heating, cooling, or mixing substances, the total weight of matter is conserved.” In plain terms, measure and graph to show that weight is conserved when matter changes.
What do I need to teach this lesson?
Balance, sealable jars and bags, vinegar, baking soda, ice, sugar, graph paper for mass-before against mass-after and the printable practice sheet linked at the end of this plan. Everything listed is either ordinary classroom equipment or a free printable from this site — there is nothing to buy and nothing to prepare beyond photocopying.
What mistakes should I expect in this lesson?
Three, each a reasoning error rather than carelessness: concludes matter is destroyed from the open jar; uses a different balance for the second reading and thinks dissolving reduces mass. The plan gives the thinking behind each one and the teaching move that addresses the thinking rather than the symptom.
How do I know whether the lesson worked?
The exit ticket asks: “An open jar of vinegar and soda loses 3.5 g; a sealed one loses none. What does that show?.” Matter is conserved; the gas escaped from the open jar rather than being destroyed. Concluding destruction means the sealed comparison needs another run. That tells you whether the class needs a reteach or a thirty-second conversation before you plan tomorrow.
Is there a worksheet to go with Weighed Before, Weighed After?
Yes — 1 printable 5-PS1-2 worksheet, linked at the end of the plan and free like the rest of the site. Each one comes with an answer key and 25 versions, so the practice after the lesson can be a different paper on every desk.
Is Weighed Before, Weighed After free to use?
Yes. The plan, its printables and their answer keys are free to read, print and photocopy for your own class, with no account and no email capture. It was last reviewed on 8 September 2026. Please do not resell it or republish it as your own.
Last reviewed 2026-09-08. Aligned to 5-PS1-2 of the Next Generation Science Standards.