Reaction Lab
A free virtual lab for the signs of a chemical reaction. Mix real lab chemicals, watch golden rain and pink potions appear, and collect the evidence that a new substance formed.
What students do
Students work through a virtual version of the classic "Chemical Reaction Indicators" lab with their partner, Dr. Pugrilla. At each station they first inspect the reactants and record their properties. Then they squeeze 15 drops of each chemical into a test tube and watch closely as the drops hit. Next they use three observation tools: a magnifying glass, a thermometer, and wafting to safely smell. Finally they check off which of the six signs of a chemical reaction they saw. The lab gives targeted feedback on wrong answers. Then students see the word equation, with color-coded chips that show the atoms swapping partners, and identify which product caused what they observed.
Copper sulfate + barium chloride, silver nitrate + sodium iodide, NaOH + phenolphthalein, lead nitrate + potassium iodide, permanganate + vitamin C.
Students predict what happens when they pour Tube A★ into Tube C★, then compare their prediction to the result.
Elephant toothpaste, a baking soda balloon, burning magnesium, and a toasted marshmallow show gas, light, odor, and temperature change.
A quick quiz with trick questions, plus a free-mixing bench with 19 reactions to discover.
The science behind Reaction Lab
Evidence of a chemical reaction
A chemical reaction makes new substances with new properties.
Atoms are far too small to see rearranging, so scientists look for evidence instead. Reaction Lab teaches six signs: a color change, gas production, light or combustion, a new odor, a temperature change, and a precipitate. Students earn a badge for each sign. They need the bonus stations to collect all six, because the worksheet reactions only show color changes and precipitates.
Precipitates and double replacement
AB + CD → AD + CB
When two clear solutions are mixed, their dissolved ions can swap partners. If a new pair cannot stay dissolved, it forms a solid called a precipitate. Students see barium sulfate snow out as white specks, silver iodide as a pale yellow cloud, and lead iodide as glittering "golden rain." The equation chips are color-coded by ion, so students can see that the same pieces appear on both sides of the arrow, just with new partners.
Properties before and after
Every Lab Mode station starts with students inspecting each reactant's color, clarity, state, temperature, and smell, and ends with a before-and-after comparison. This is the heart of NGSS MS-PS1-2. The lab also builds careful thinking about evidence. For example, the vinegar in Station G smelled sour before the reaction, so that odor does not count. In Station I, the burner flame heats the marshmallow, so its temperature change does not count unless the marshmallow catches fire and starts giving off its own heat.
Conservation of mass
Atoms are rearranged, not created or destroyed.
A "Why?" button on every products screen explains that the atoms in the products were already in the reactants. One answer choice even asks whether the yellow solid could be gold. It can't, because no gold atoms went into the tube.
NGSS alignment
Reaction Lab supports the following Next Generation Science Standards for middle school physical science.
| Standard | What it says | How the lab supports it |
|---|---|---|
| MS-PS1-2 | Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred. | Students record reactant properties, collect evidence with three tools, compare before and after, and decide which signs of a reaction occurred. |
| MS-PS1-5 | Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved. | Color-coded equation chips show the same atoms on both sides of each reaction. |
| MS-PS1-6 | Undertake a design project to construct, test, and modify a device that either releases or absorbs thermal energy by chemical processes. | Supporting background: students measure an exothermic reaction (elephant toothpaste warms up) and an endothermic one (baking soda and vinegar cools down). |
| DCI PS1.A, PS1.B | Structure and Properties of Matter; Chemical Reactions | Every station, plus the Chemical or Physical? challenge. |
| Crosscutting concepts | Patterns; Energy and Matter | Students notice which reactant pairs make precipitates in Explore Mode, and track energy given off or taken in. |
How to use it in class
- Hook (5 min). Ask: "If you mix two clear liquids, can you get a solid?" Have students commit to yes or no.
- Lab (30 min). In Lab Mode, students complete Stations A through E and the Mystery Mix. Each station takes about four minutes.
- Bonus (10 min). Early finishers do Stations F through I to collect all six signs, then play Chemical or Physical?
- Notebook and submit (5 min). Students list five signs of a chemical reaction and three questions they have in the notebook, then screenshot their lab report.
- Debrief. Use the discussion questions below.
It also works as a pre-lab before running the real reactions, or as a make-up lab for absent students.
Discussion questions
- In Station A, two liquids made a solid. Where did the solid come from?
- Boiling water makes bubbles. Is that a chemical reaction? What else would you need to know?
- What was your prediction for the Mystery Mix? Why did the pink disappear?
- The marshmallow got hot over the burner. Why didn't that count as a temperature change?
- Which sign of a chemical reaction do you think is the most convincing? Which is the easiest to be fooled by?
Key vocabulary
Chemical reaction, chemical change, physical change, reactant, product, precipitate, indicator, exothermic, endothermic, double replacement, decomposition, synthesis, combustion, conservation of mass.
Frequently asked questions
Is Reaction Lab free?
Yes. It runs free in any web browser with no ads, no download, and no login.
What are the six signs of a chemical reaction in the lab?
Color change, gas production, light or combustion, a new odor, a temperature change, and the formation of a precipitate. Students collect a badge for each sign as they find evidence of it.
Is the chemistry accurate?
Yes. Every reaction shows its real result: barium sulfate forms a white precipitate, silver iodide is pale yellow, lead iodide forms bright yellow golden rain, phenolphthalein turns pink in sodium hydroxide, vitamin C turns purple permanganate colorless, and mixing copper chloride with sodium hydroxide makes light blue copper hydroxide.
Why use a virtual lab for these reactions?
Several classic indicator reactions use chemicals that are toxic or hard to get, like lead nitrate, barium chloride, and silver nitrate. The virtual lab lets every student run every reaction safely, as many times as they want, and works as a make-up lab for absent students.
What is the difference between Lab Mode and Explore Mode?
Lab Mode walks students through each station step by step: observe the reactants, add 15 drops of each chemical, use three observation tools, record the signs, and identify the products. Explore Mode is a free-mixing bench where students combine any two of ten chemicals to discover all 19 reactions.