Instructions
Read through the questions below which relate to the experiments in your Mel Science kits. Answer each question in the space provided, using your observations and scientific knowledge. These experiments explore the fascinating fields of electrochemistry, energy transformation, and corrosion.
Part 1: Chemistry & Electricity
These questions relate to the Lemon Battery and the Daniel Galvanic Cell experiments.
1. What type of energy transformation occurs in both the lemon battery and the Daniel cell?
2. A simple electrochemical cell has four main components. Identify the role of the following in the lemon battery:
- Anode (Negative Electrode): _________________________
- Cathode (Positive Electrode): _________________________
- Electrolyte: _________________________
- External Circuit (Conductor): _________________________
3. Both zinc and copper are used as electrodes. Based on your observations (the LED lights up), which metal is more reactive? Explain how you know.
4. The Daniel cell uses solutions of copper(II) sulfate and zinc sulfate. Why is this cell generally more powerful and reliable than the lemon battery?
Part 2: Corrosion Chemistry
These questions relate to the Rust Protection and Electricity vs Iron experiments.
5. Rusting is the common name for the corrosion of iron. What type of chemical reaction is it? What are the two main substances required for iron to rust?
6. In the rust protection experiment, you likely connected an iron nail to a more reactive metal like a magnesium strip. This method is called "sacrificial protection". Explain in your own words how this protects the iron from rusting.
7. The indicator potassium hexacyanoferrate(III) turns blue in the presence of iron(II) ions (Fe2+). What does the appearance of a blue colour tell you is happening to the iron metal?
Part 3: Connecting to the Big Ideas (Australian Curriculum Links)
Match the scientific concepts from the curriculum (listed below) to the experiment that best demonstrates it. An experiment can be used more than once. Write the experiment number (1a, 1b, 2a, 2b) next to the concept it demonstrates.
Experiments:
1a. Lemon Battery | 1b. Daniel Galvanic Cell | 2a. Rust Protection | 2b. Electricity vs Iron
| Scientific Concept (from the Year 8-10 Curriculum) | Matching Experiment(s) |
|---|---|
| Chemical energy is transformed into electrical energy. | |
| The properties of different metals (like reactivity) determine their use. | |
| Chemical reactions involve the transfer of electrons from one substance to another (oxidation and reduction). | |
| The rate of a chemical reaction (like corrosion) can be controlled or influenced by different factors. | |
| An external energy source (like a battery) can be used to drive a non-spontaneous chemical reaction. |
Answer Key
Part 1: Chemistry & Electricity
Chemical energy stored in the substances is transformed (or converted) into electrical energy.
- Anode (Negative Electrode): The zinc wire/strip (it is oxidized).
- Cathode (Positive Electrode): The copper wire (reduction occurs here).
- Electrolyte: The citric acid within the lemon juice.
- External Circuit (Conductor): The wires and the LED that the electrons flow through.
Zinc is more reactive. In a galvanic cell, the more reactive metal gives up its electrons (is oxidized) and becomes the negative anode. The flow of these electrons from zinc to copper through the wire is what creates the electric current.
The Daniel cell is more efficient because it uses solutions with a high concentration of mobile ions (from the dissolved salts) as electrolytes, which is much better at conducting charge than lemon juice. It also keeps the oxidation and reduction reactions separate, which allows for a more stable and higher voltage.
Part 2: Corrosion Chemistry
Rusting is an oxidation-reduction (redox) reaction. The two substances required are oxygen and water.
Magnesium is more reactive than iron, meaning it loses its electrons more easily. When connected to iron, the magnesium corrodes (oxidizes) "sacrificially" instead of the iron. The magnesium gives its electrons to the iron, preventing the iron from losing its own electrons to oxygen and thus protecting it from rusting.
The blue colour indicates that solid iron metal (Fe) is losing electrons and turning into iron(II) ions (Fe2+). This is the first step of the rusting process (oxidation). Therefore, blue colour means the iron is corroding in that area.
Part 3: Connecting to the Big Ideas (Australian Curriculum Links)
This table shows how the concepts demonstrated in the experiments link to the ACARA v9 Science Understanding strand (Chemical sciences sub-strand).
| Scientific Concept | Matching Experiment(s) | Relevant ACARA Achievement Standard Links (Years 8-10) |
|---|---|---|
| Chemical energy is transformed into electrical energy. | 1a, 1b | Year 8 (AC9S8U07): Investigating energy transfer and transformation in systems. |
| The properties of different metals (like reactivity) determine their use. | 1a, 1b, 2a | Year 9 (AC9S9U07): Relating atomic structure to properties of elements. Reactivity is a key chemical property. |
| Chemical reactions involve the transfer of electrons from one substance to another (oxidation and reduction). | 1a, 1b, 2a, 2b | Year 10 (AC9S10U07): Explaining different types of chemical reactions. Redox is a fundamental type of reaction. |
| The rate of a chemical reaction (like corrosion) can be controlled or influenced by different factors. | 2a, 2b | Year 10 (AC9S10U08): Investigating how reaction rates can be influenced. Sacrificial protection and applied currents influence the rate of corrosion. |
| An external energy source (like a battery) can be used to drive a non-spontaneous chemical reaction. | 2b | Year 10 (AC9S10U07 / Senior Chemistry concepts): This is the basis of electrolysis, which is a key type of chemical reaction driven by electrical energy. |