Questions:
How can we identify that a chemical reaction has occurred? What evidence shows that burning something is a chemical reaction?
Hypothesis:
Write your hypotheses as: If… then… because…
Objective:
Observe and explain evidence of a chemical reaction through the combustion of magnesium, identifying changes in matter and energy.
EXPERIMENT 1:
Materials:
- Magnesium ribbon
- Bunsen burner
- Tongs
- Heat-resistant surface / watch glass
Procedures:
- Put on your safety goggles.
- Light up the bunsen burner.
- Hold the magnesium ribbon with tongs.
- Carefully place the ribbon in the flame.
- Observe what happens during the burning process.
- After the reaction, observe the material formed. Place it in the watch glass.
- Record all observations.
Results:
Observe and record:
- Changes in color
- Emission of light
- Release of heat
- Formation of smoke or powder
- Differences between the initial and final substances
Discussion:
- What changes were observed during the reaction?
- Did the reaction produce energy? How do you know?
- Was a new substance formed? What evidence supports your answer?
- Is the final material equal to the original magnesium? Why?
- What characteristics indicate that this was a chemical reaction?
Conclusion:
Is burning magnesium a chemical or a physical reaction? Why? Is your hypothesis correct? Why?
EXPERIMENT 2:
Objective:
Investigate a chemical reaction between potassium permanganate and glycerin by identifying signs of transformation and energy release.
Materials:
- Potassium permanganate crystals
- Glycerin (glycerol)
- Mortar or crucible
- Spatula
- Safety goggles
- Gloves
Procedures:
- Put on safety goggles and gloves.
- Place a small amount of potassium permanganate on the crucible.
- Add a few drops of glycerin onto the crystals.
- Observe carefully without touching the mixture.
- Wait and record all visible changes.
Results:
Observe:
- Delay before the reaction starts
- Color changes
- Smoke formation
- Release of heat
- Fire or sparks
- Formation of residues
Discussion Questions:
- What happened after the substances were mixed?
- Did the reaction happen immediately?
- What evidence showed that energy was released?
- Was a new substance formed?
- Why is this considered a chemical reaction?
Conclusion
The mixture of potassium permanganate and glycerin causes a chemical or a physical reaction? Explain why. Is your hypothesis correct? Why?
Final Reflection (for both experiments)
Comparative Analysis
On a new paper, in groups, copy and complete the table below with your observations:
| Evidence of Chemical Reaction | Magnesium | Permanganate + Glycerin |
|---|---|---|
| Light produced | ||
| Heat released | ||
| Color change | ||
| New substance formed | ||
| Smoke/gas produced |