When matter meets matter — is it a mixture, or something brand new?
📋 NGSS Standard:5-PS1-4 — Conduct an investigation to determine whether the mixing of two or more substances results in new substances.
🎯 Learning Objectives
Students will:
Distinguish between a mixture (substances combined but not chemically changed) and a chemical reaction (new substance formed with different properties)
Identify evidence of a chemical reaction: color change, gas production, temperature change, precipitate formation, and light/energy release
Design and conduct a controlled investigation testing whether mixing produces a new substance
🔑 Key Vocabulary
Reactant — A starting substance that enters a chemical reaction
Product — A new substance formed as a result of a chemical reaction
Mixture — Two or more substances combined but not chemically changed; each substance keeps its own properties and can be separated
Chemical reaction — A process where reactants combine to form products with new, different properties
Evidence — Observable changes that indicate a chemical reaction occurred (gas, color change, temperature change, precipitate formation, light)
Precipitate — A solid that forms when substances react (the milk curds in today's experiment are a precipitate — a solid that appeared from a liquid mixture)
🔬 The Big Idea
When you combine substances, two very different things can happen:
🥄 Mixture
The substances are combined but not changed. Each ingredient keeps its own properties. You could separate them back out — no new substance was made.
Example: Salt + water. The salt dissolves, but evaporate the water and your salt comes back!
⚗️ Chemical Reaction
The substances react and form something new. The starting materials are transformed — you can't get them back. New properties appear.
Example: Baking soda + vinegar. The fizzing CO₂ gas is a brand-new substance!
💡 How do you know a reaction happened? Look for these clues: fizzing/bubbles (gas produced), color change, temperature change (feels warmer or colder), a solid forming in a liquid (precipitate), or light/energy released.
📦 Materials
🏠 Pantry Items
Baking soda
Baking powder
White vinegar
Whole milk (or 2%)
Salt
Sugar
Sand (optional — grab some from outside, or skip)
Lemon (or bottled lemon juice)
🧰 Equipment
6–8 small cups or glasses
Spoons for stirring
Baking sheet or tray (to contain spills!)
Student Worksheet (last pages of this lesson)
Pencil for recording observations
⚠️ Safety Note: All materials are household food-grade items — safe for 5th graders. Vinegar is a mild acid; avoid splashing it near eyes. Do the experiments on a tray — baking soda + vinegar can overflow small cups!
🔬 The Investigation
This experiment has three parts. Record all observations on the Student Worksheet as you go.
Part 1 — Mixtures (No New Substance)
Test these combinations. Predict first — will anything exciting happen?
Experiment 1A — Salt + Water
Add a teaspoon of salt to a half-cup of water. Stir. Observe and record. Does it dissolve? Any gas? Any color change? Any heat?
Key question: Where did the salt go? Did it disappear?
Experiment 1B — Sand + Water (skip if no sand available)
Add a spoonful of sand to water. Stir vigorously. Observe. Does the sand dissolve? What happens when you stop stirring?
Key question: Is the sand still sand?
Experiment 1C — Baking Soda + Sugar
Mix a teaspoon of baking soda with a teaspoon of sugar in a dry cup. Stir. Observe. Any change? Any new properties?
Key question: Could you separate these if you had to?
💡 What to notice: No color change, no gas, no temperature change, no new properties. These are physical combinations — mixtures. The substances are all still themselves.
Part 2 — Chemical Reactions (Something New Forms)
Now things get interesting. Watch closely and record every observation.
Experiment 2A — Baking Soda + Vinegar ⭐
Place 1 teaspoon of baking soda in a cup on your tray. Slowly pour in 2 tablespoons of white vinegar. Step back and observe!
Carefully touch the outside of the cup with your hand. Does it feel warmer, cooler, or the same?
What you'll see: vigorous fizzing (CO₂ gas!), and the cup feels slightly cooler to the touch.
Experiment 2B — Milk + Vinegar
Add 2 tablespoons of milk to a cup. Add 1 tablespoon of white vinegar. Stir gently. Let it sit for 2–3 minutes. Observe what forms.
Gently pour off the liquid. Touch the solid that remains.
What you'll see: white curds form — a rubbery solid called casein. This is the same protein used to make early plastics!
Experiment 2C — Lemon Juice + Baking Soda
Squeeze (or pour) 2 tablespoons of lemon juice into a cup. Add 1 teaspoon of baking soda. Observe.
What you'll see: fizzing — same chemistry as 2A, but lemon juice is a weaker acid than vinegar, so it's gentler.
💡 Compare Parts 1 and 2: What's different? Part 2 produced gases, solids, and temperature changes. Those are clues that new substances formed — the reactants rearranged into products.
Part 3 — 🔍 The Mystery Challenge (Optional Extension)
This challenge is optional. If your family is ready for more, give it a try! Otherwise, skip to the Discussion Questions.
🔍 Mystery Powder Identification
Your parent has prepared an unlabeled powder for you. It is either baking soda or baking powder. Your job: figure out which one it is using only the evidence you collect.
Your tools: water and white vinegar (test each separately)
Add a small amount of the mystery powder to one cup. Add water only. Observe.
Add a small amount of the mystery powder to a second cup. Add vinegar. Observe.
Compare to what you know from Parts 1 and 2. Record your observations and your conclusion on the Student Worksheet.
The clue: baking powder already contains an acid (cream of tartar), so it fizzes with water alone. Baking soda is a pure base — it only fizzes when you add an acid like vinegar.
⚗️ The Science Behind the Reactions
Science Snapshot
Some changes only combine materials, but chemical reactions create products with new properties.
What is happening?
A mixture is a physical combination of substances, while a chemical reaction rearranges atoms to make new substances. Reactants are the starting materials, and products are the new substances formed after the reaction.
Why it works that way
Students can often spot a reaction by evidence such as gas bubbles, temperature change, color change, smell change, or a solid precipitate. Those clues matter because they suggest the particles were rearranged, not merely stirred together.
Look for this in the lesson
Students should compare “mixed but still the same materials” with “new substances formed.” The investigation gets more scientific when they explain which observations count as evidence for each case.
Ask while you read: Which observations suggest a new substance formed instead of a simple mixture?
💬 Discussion Questions
🗣️ Question 1: "You mixed baking soda and vinegar and got CO₂ gas. Where did the gas come from? Was it in the baking soda, the vinegar, or did it form during the reaction?"
The gas formed during the reaction. Neither the baking soda nor the vinegar contained CO₂ gas — the atoms rearranged into a new arrangement (carbon dioxide) as a product. Specifically, the carbon in CO₂ came from the bicarbonate in the baking soda, and the vinegar's acid triggered the decomposition. This is what makes it a chemical reaction: atoms don't appear or disappear, they just rearrange into new molecules.
🗣️ Question 2: "Your milk curdled when you added vinegar. Is that reversible? Could you get your milk back?"
No — this is why it's a chemical reaction and not a mixture. The proteins changed shape permanently (denaturation) and the casein formed new molecular bonds clumping into curds. You can't uncurl a protein. In contrast, salt dissolved in water can be recovered — just evaporate the water. Reversibility is one clue (though not a perfect rule) for distinguishing physical from chemical changes.
🗣️ Question 3: "Scientists say 'matter is neither created nor destroyed.' But you added baking soda and vinegar and got a pile of foam that seemed to appear from nowhere. How does that work?"
The foam is the reactants — they just changed form. The CO₂ gas comes from the bicarbonate in the baking soda decomposing when the acid from vinegar was added. The total mass of baking soda + vinegar equals the total mass of sodium acetate + water + CO₂ gas that escapes (law of conservation of mass). If you could capture all the gas and weigh everything, the scales would balance. Nothing was created or destroyed — just rearranged.
🚀 Extensions
🧮 Word equation challenge: Can you write the word equation for the baking soda + vinegar reaction? (baking soda + vinegar → carbon dioxide + water + sodium acetate)
🍳 Cooking connections: Cooking is chemistry! Baking powder in muffins, eggs setting when heated, browning meat (Maillard reaction). Find three examples of chemical reactions in your kitchen.
🌧️ Real-world reactions: Rusting = iron + oxygen → iron oxide. Burning = fuel + oxygen → CO₂ + water + energy. Both are chemical reactions. What evidence tells you something reacted?
⚖️ Conservation of mass experiment: Weigh the baking soda and vinegar separately. Mix them in a sealed bag. Weigh the bag. Does the total mass change? Why or why not?
📚 Further reading: Look up the Maillard reaction — it's what makes toast brown and steak delicious. Pure chemistry in your kitchen every day!
👩🏫 Parent/Teacher Notes
Use a tray: Do all experiments on a baking sheet or tray. Baking soda + vinegar can overflow a small cup if you add too much. Keep amounts small: 1 tsp baking soda + 2 tbsp vinegar is plenty.
Milk reaction timing: Use about 2 tablespoons of milk + 1 tablespoon of vinegar. Stir and let sit 2–3 minutes before draining. The rubbery solid is casein — have students feel it! It's fascinating.
Mystery challenge: This is the best part. Give the unlabeled powder without revealing which it is. Let students work it out from evidence before you confirm. If they need a hint: "What happened when you added just water to each?" Baking powder fizzes with water alone; baking soda does not.
Sand is optional: If you don't have clean sand, simply skip Experiment 1B. The lesson works fine without it.
For advanced students: Can they write the full word equations for each reaction? Can they explain why some reactions release heat (exothermic) while baking soda + vinegar absorbs heat (endothermic)?
Real-world connections: Cooking is chemistry. Baking powder in muffins rises because of the baking soda + acid reaction. Eggs set when heated because proteins denature (like the casein). These are all chemical reactions students eat every day!
Safety: All materials are food-grade and safe. Vinegar may irritate eyes — don't splash. No flames, no heat sources required for any experiment.
NGSS alignment: This lesson fully addresses 5-PS1-4. Students design and conduct investigations (Part 3 mystery), gather evidence (data table), and make evidence-based conclusions about whether new substances form.
1. List 3 pieces of evidence that tell you a chemical reaction occurred:
① _____________________________________________________________________________
② _____________________________________________________________________________
③ _____________________________________________________________________________
2. What is the difference between a reactant and a product? Give an example from today's investigation:
🖊️ Diagram — Label the Reaction
Label the diagram below for the baking soda + vinegar reaction. Write the names of the reactants in the left boxes and the products in the right boxes. Add arrows to show the direction of the reaction.
Reactant 1:
(write name)
starting substance
+
Reactant 2:
(write name)
starting substance
→
Products:
(write all 3)
new substances formed
Hint: there are 3 products — gas, liquid, and a dissolved substance
🔑 PARENT/TEACHER ANSWER KEY — Detach before giving to student
📊 Data Table — Expected Answers
Experiment
What to Observe
Gas?
Color Change or Precipitate?
Cup Warmer/Cooler?
Reversible?
Mixture or Reaction?
Salt + Water
Salt dissolves; clear salty solution
N
N
N
Y (evaporate water)
Mixture
Sand + Water
Sand sinks/suspends; doesn't dissolve
N
N
N
Y (filter/settle)
Mixture
Baking Soda + Sugar
Powders mix; no new properties
N
N
N
Y (could be separated)
Mixture
Baking Soda + Vinegar
Vigorous fizzing/foam; cools slightly
Y (CO₂ gas)
N
Y (cools)
N (irreversible)
Reaction
Milk + Vinegar
Milk curdles; rubbery white casein forms
N
Y (precipitate forms)
N
N (can't un-curdle)
Reaction
Lemon Juice + Baking Soda
Fizzing (gentler), bubbles visible
Y (CO₂ gas)
N
Slight
N (irreversible)
Reaction
🔍 Mystery Powder — Key
If the mystery powder is baking soda: Water → no fizzing. Vinegar → vigorous fizzing. Conclusion: baking soda.
If the mystery powder is baking powder: Water → slight fizzing (the built-in acid activates). Vinegar → vigorous fizzing (extra acid added). Conclusion: baking powder, because it fizzes with water alone.
Note: baking powder contains baking soda + cream of tartar (an acid) + a starch. The acid is already inside, so just adding water is enough to start the reaction.
✏️ Short Answer — Model Answers
1. Three pieces of evidence of a chemical reaction:
Any three of: gas/bubbles produced, color change, temperature change (warmer or cooler), a precipitate (solid) forming, light or energy released, irreversibility. Students should cite specific observations from today's experiments.
2. Reactant vs. product:
A reactant is a starting substance — it enters the reaction. A product is a new substance formed by the reaction. Example: in baking soda + vinegar, the baking soda and vinegar are the reactants. Carbon dioxide gas, water, and sodium acetate are the products. The key difference is that products have new properties the reactants didn't have.
🖊️ Diagram — Baking Soda + Vinegar
Reactant 1: Baking soda (sodium bicarbonate / NaHCO₃)
Reactant 2: Vinegar (acetic acid / CH₃COOH)
Products: Carbon dioxide gas (CO₂) + water (H₂O) + sodium acetate (NaCH₃COO)
Accept "baking soda" and "vinegar" as correct names; chemical formulas are a bonus for advanced students.
✅ Success Criteria
Student correctly classifies all 6 experiments as mixture or reaction (minor errors acceptable — discuss together).
Student can identify at least 2 pieces of evidence of a chemical reaction from their own observations.
Student can explain in their own words: reactants go in, products come out, something new is formed.
Student correctly identifies the mystery powder using evidence.
You're seeing a preview. Full-library access is not live yet. For now, browse the live store products and free sample lessons while the larger subscription offer stays in Coming Soon. Live now: free samples + Kitchen Chemistry.
