Electrochemistry & Corrosion Worksheet for 15‑Year‑Olds — Mel Science Starter Kit

Instructions

Read each question carefully and answer based on the principles you observed during your MEL Science experiments. Use your knowledge of chemistry to explain the "why" behind the reactions.

Section 1: Lab Safety & Fundamentals

Before any experiment, safety is the top priority. Answer the following based on your starter kit materials.

1. Why is it crucial to wear safety glasses during these chemistry experiments, even if you think a reaction is gentle?


2. What is the primary purpose of the plastic tray provided in your kit?
   a) To use as a cutting board
   b) To contain spills and protect surfaces
   c) To measure liquids accurately
   d) To mix chemicals in

Section 2: Chemistry & Electricity

These questions relate to the experiments where you generated electricity using chemical reactions.

Part A: The Lemon Battery

In this experiment, you used a lemon, a zinc wire, and a copper wire to power an LED.

3. The lemon juice, which contains citric acid, serves a critical role in the battery. It is the electrolyte, a substance that contains ions and can conduct electricity.
4. In any electrochemical cell, there are two electrodes: the anode and the cathode. Oxidation occurs at the anode, and reduction occurs at the cathode. Given that zinc is more reactive than copper, which metal acts as the anode (loses electrons)?
   
   Anode: _________________________


5. Explain why using two identical wires (e.g., two copper wires) would not work to create a functioning battery.

Part B: The Daniell Cell

This experiment uses zinc wire in zinc sulfate (ZnSO₄) and copper wire in copper(II) sulfate (CuSO₄) to create a more efficient electrochemical cell.

6. The overall process involves the transfer of electrons. This type of reaction, involving both oxidation and reduction, is called a _______________ reaction.


7. At the anode, the more reactive metal, zinc, is oxidized. Complete the chemical half-reaction for this process:
   
   Zn_(s) → Zn²⁺_(aq) + _____ e^-


8. At the cathode, copper ions from the copper(II) sulfate solution are reduced. Complete the chemical half-reaction for this process:
   
   Cu²⁺_(aq) + _____ e^- → Cu_(s)


9. In which direction do the electrons flow through the external wire connecting the two electrodes?
   a) From Copper to Zinc
   b) From Zinc to Copper
   c) There is no flow of electrons.
   d) The flow is random.

Section 3: The Science of Corrosion

These questions relate to the experiments involving the rusting of iron and methods to prevent it.

10. Rusting is the common name for the corrosion of iron. Chemically, it is the oxidation of iron. What two substances are required from the environment for iron to rust?
    
    1. _________________________
    2. _________________________


11. In one experiment, you likely observed how to protect an iron nail from rusting using a strip of magnesium. Magnesium is more reactive than iron. When the two are in contact in an electrolyte (like salt water), the magnesium corrodes preferentially, "sacrificing" itself to protect the iron. What is the name for the magnesium in this scenario?
    a) The Primary Anode
    b) The Cathodic Protector
    c) The Sacrificial Anode
    d) The Inert Electrode


12. The indicator potassium hexacyanoferrate(III) is used to detect the presence of Iron(II) ions (Fe²⁺), which are formed when iron begins to corrode. It turns a deep blue color (Prussian blue) in their presence. If you set up an experiment with an iron nail alone and an iron nail wrapped in magnesium, in which Petri dish would you expect to see the most intense blue color? Explain your reasoning.

Section 4: Concept Connection

13. What is the single, fundamental concept that connects the lemon battery, the Daniell cell, and the corrosion of iron? Explain how this concept applies to all three scenarios.

Answer Key

1. Safety glasses protect your eyes from splashes of chemicals or small projectiles from an unexpected reaction. Eyes are extremely sensitive and damage can be permanent.


2. b) To contain spills and protect surfaces


3. (This is a statement, no answer required.)


4. Anode: Zinc


5. A battery requires a difference in electrical potential to drive the flow of electrons. This potential difference is created by using two different metals with different reactivities (different tendencies to lose electrons). Two identical metals would have no potential difference between them, so no electrons would flow.


6. Redox (or Oxidation-Reduction)


7. Zn_(s) → Zn²⁺_(aq) + 2 e^-


8. Cu²⁺_(aq) + 2 e^- → Cu_(s)


9. b) From Zinc to Copper


10. 1. Oxygen (usually from the air)
    2. Water


11. c) The Sacrificial Anode


12. You would expect to see the most intense blue color in the Petri dish with the iron nail alone. This is because the unprotected nail is free to oxidize (corrode), producing the Fe²⁺ ions that react with the indicator. The nail wrapped in magnesium is protected; the magnesium oxidizes instead, so very few (if any) Fe²⁺ ions are formed.


13. The fundamental concept is Redox (Oxidation-Reduction) Reactions, which involve the transfer of electrons.
    - Lemon Battery/Daniell Cell: These are examples of galvanic cells that harness a spontaneous redox reaction to produce electricity. A more reactive metal (like zinc) is oxidized (loses electrons) and a less reactive metal (or its ions, like copper) is reduced (gains electrons), causing a flow of electrons that can power a device.
    - Corrosion: This is an unwanted spontaneous redox reaction. Iron is oxidized (loses electrons) by oxygen in the presence of water, forming rust. The principles of electrochemistry are used to prevent it, for example, by providing a more easily oxidized metal (a sacrificial anode) to be corroded instead.