Instructions
Pray, attend to the following scientific inquiries with diligence and a keen eye. You are to undertake two experiments of a chemical nature, documenting your observations and deductions in the manner prescribed by the Cornell method of note-taking. This system, a most excellent tool for the organised mind, requires you to record your notes in the main column, formulate questions or keywords in the smaller column, and, upon completion, compose a summary of your learning at the foot of the page.
Australian Curriculum Alignment (ACARA v9)
These investigations align with the following standards of learning, which a student of good standing is expected to master.
- Year 8 Science: Investigate the properties and interactions of materials, including the chemical reactions of acids and metals, and the conservation of mass (AC9S8U07). Model the rearrangement of atoms in chemical reactions.
- Year 9 Science: Investigate how chemistry can be used to produce a range of useful substances, including knowledge of atomic structure and chemical reactions, such as the transfer of electrons in redox reactions (AC9S9U06, AC9S9U07). Explain how the properties of substances are related to their chemical structure.
Teacher's Compendium: Analytic & Scoring Rubrics
Presented in a manner befitting a scholar of discerning taste.
Experiment 1: Rust Protection – A Tale of Sacrificial Metal
A Rubric for the Year 8 Scholar
| Criterion of Assessment | A Most Accomplished Performance | A Commendable Effort | A Matter Requiring Further Tutelage |
|---|---|---|---|
| Observation & Record | The scholar hath documented, with meticulous detail, all visible transformations, noting colours and textures with the precision of a seasoned naturalist. | Observations are recorded with sufficient accuracy, though they may lack the finer points of descriptive language. | The account is sparse, betraying a want of attention to the subtle changes wrought by the experiment. |
| Interpretation of Events | A most sagacious connection is made between the observed protection of the iron and the presence of the second metal, using the term 'corrosion'. | The scholar correctly identifies that one metal has prevented the other from rusting, yet the explanation remains of a simple nature. | There is little to no attempt to explain the reason for the observed outcome, showing a misunderstanding of the central principle. |
A Rubric for the Year 9 Scholar
| Criterion of Assessment | A Most Accomplished Performance | A Commendable Effort | A Matter Requiring Further Tutelage |
|---|---|---|---|
| Observation & Record | The documentation is exemplary, noting not only which metal corrodes but also the relative rate and nature of the corrosion, with flawless scientific vocabulary. | Observations are accurate and correctly recorded, identifying the sacrificial metal and the protected metal. | The record is incomplete or contains inaccuracies regarding the specific changes to each metallic component. |
| Chemical Justification | The scholar explains the phenomenon with profound insight, correctly employing terms such as 'galvanic protection', 'anode', 'cathode', and referencing the relative reactivity of the metals. | A sound, albeit simplified, explanation is furnished, correctly identifying the more reactive metal as the one that 'sacrifices' itself. | The explanation is confused, failing to correctly apply the principles of electrochemistry or the activity series to the observed result. |
Experiment 2: Electricity vs Iron – A Most Shocking Duel
A Rubric for the Year 8 Scholar
| Criterion of Assessment | A Most Accomplished Performance | A Commendable Effort | A Matter Requiring Further Tutelage |
|---|---|---|---|
| Observation & Record | With keen perception, the scholar notes the dissolution of the iron strip, the formation of gas, and the change in the solution's colour, recording all with laudable clarity. | The main observations, such as the iron strip shrinking, are noted, but subtler details may be overlooked. | The account is vague and lacks the specific details required to understand the transformation that has occurred. |
| Conceptual Understanding | The scholar correctly deduces that electricity is a form of energy that can cause a chemical change, rightly concluding it is responsible for dismantling the iron. | A connection is made between the electric current and the changes observed, though the explanation of *how* it causes the change is elementary. | There is a failure to link the application of electricity to the chemical reaction, showing a want of comprehension. |
A Rubric for the Year 9 Scholar
| Criterion of Assessment | A Most Accomplished Performance | A Commendable Effort | A Matter Requiring Further Tutelage |
|---|---|---|---|
| Observation & Record | Every phenomenon is meticulously recorded: the precise electrode where dissolution occurs, the identity of the gas produced (hypothesised or tested), and the nature of the precipitate formed. | The scholar correctly identifies the changes at both the positive and negative electrodes, though the description may lack full scientific rigour. | The record is muddled, failing to distinguish between the events at the anode and the cathode. |
| Electrochemical Analysis | The process is correctly identified as electrolysis. The scholar explains the events using the terms 'oxidation' at the anode and 'reduction' at the cathode, and may even propose the relevant half-equations. | The scholar identifies that the electricity breaks down the substances but struggles to articulate the specific electron transfer processes of oxidation and reduction. | The explanation is incorrect, confusing the roles of the electrodes or the fundamental principles of electrolysis. |
Simplified Instructor Scripts
Script 1: Rust Protection
Safety First: Ensure safety goggles are worn. Handle chemicals with care.
- "First, we shall prepare our testing ground. Pour the sodium chloride (NaCl) and potassium hexacyanoferrate(III) (K₃[Fe(CN)₆]) solutions into a petri dish and add water as directed. Stir until all is dissolved. This solution will reveal rust by turning blue."
- "Next, prepare your subjects. Take two iron nails. Tightly wrap a small piece of zinc (Zn) wire around one nail. Tightly wrap a small piece of copper (Cu) wire around the other."
- "Place both prepared nails, along with a third, unwrapped iron nail, into the petri dish. Ensure they are submerged but not touching one another."
- "Now, we observe. It shall take some time, perhaps 10 to 15 minutes. Record your initial observations and then watch for the first signs of change. Look closely at the iron itself and the area immediately surrounding each nail."
- "Once a distinct blue colour has appeared, you may document your final observations. Which nail shows the most rust? Which shows the least? What has happened to the zinc and copper?"
Script 2: Electricity vs Iron
Safety First: Ensure safety goggles are worn. Do not touch the electrodes or solution when the power is on. Disconnect batteries when not in use.
- "Prepare the electrolyte. Dissolve the sodium sulfate (Na₂SO₄) in water in a beaker or petri dish."
- "Attach two alligator clips to your battery holder. We shall designate one positive (the anode) and one negative (the cathode)."
- "Clip a clean iron strip to the positive (anode) clip. Clip another clean iron strip to the negative (cathode) clip."
- "Submerge the ends of both iron strips into the sodium sulfate solution. Do not let the clips touch the water. Ensure the iron strips do not touch each other."
- "Insert the batteries to complete the circuit. Your duel begins! Observe both iron strips—the anode and the cathode—most carefully. What do you see happening at each?"
- "Note the formation of bubbles, any change in colour of the solution, and any change to the structure of the iron itself. The experiment will run for 5 to 10 minutes."
- "After observing, disconnect the batteries. Remove the strips and record your final findings."
A Treatise on Chemical Transformations
Part the First: On the Sacrificial Protection of Iron
In this inquiry, we shall investigate how one metal may offer itself up to the ravages of corrosion to preserve another. We seek to understand the hierarchy of metals in their willingness to rust.
Hypothesis: I predict that the metal which is more reactive than iron will protect it from rusting, while the metal that is less reactive will not.
| Keywords & Questions | Observations & Notes |
|---|---|
|
Initial Setup:
What is the purpose of the K₃[Fe(CN)₆] indicator? |
Initial Observations (Time = 0 minutes): Describe the appearance of the three nails and the solution before significant time has passed. |
|
Final State: Which nail rusted the most? Which nail was protected? What happened to the zinc wire? What is a 'sacrificial anode'? |
Final Observations (Time = 15 minutes): Plain Iron Nail: Iron Nail with Copper: Iron Nail with Zinc: |
Summary of LearningIn no more than three sentences, summarise the principle of sacrificial protection as demonstrated by this experiment. |
|
Part the Second: An Electrical Assault Upon an Iron Strip
Here, we shall witness the formidable power of an electrical current to compel a chemical change, forcing a sturdy iron strip to dissolve into solution. This process is known as electrolysis.
Hypothesis: I predict that the iron strip connected to the positive terminal (anode) will dissolve, while gas will form at the negative terminal (cathode).
| Keywords & Questions | Observations & Notes |
|---|---|
|
Anode (+ terminal): What is happening to the iron strip? What colour change is seen in the solution nearby? What is oxidation? |
Observations at the Anode (Positive Electrode): |
|
Cathode (- terminal): What is forming on this iron strip? What gas might this be? What is reduction? |
Observations at the Cathode (Negative Electrode): |
Summary of LearningIn no more than three sentences, summarise how electricity caused a chemical change in this experiment, referencing the two electrodes. |
|
Scaffolded Research Questions
For the Year 8 Scholar:
- Rust Protection: Ships that sail in saltwater often have large blocks of zinc attached to their steel (iron) hulls. Based on your experiment, why is this done?
- Rust Protection: What are the two main things that are required for iron to rust?
- Electricity vs Iron: In your experiment, electricity was used to break something down. Can you think of another example where electricity is used to cause a chemical change? (Hint: think about water).
- Electricity vs Iron: What evidence did you see that a chemical reaction was happening when the electricity was on? List two pieces of evidence.
For the Year 9 Scholar:
- Rust Protection: The "electrochemical series" ranks metals by their reactivity. Research this series. Where do iron, zinc, and copper sit relative to each other? Explain how their positions predict the outcome of your experiment.
- Rust Protection: Define "galvanic corrosion." Explain which metal acted as the anode (was oxidized) and which acted as the cathode (was protected) in the Fe-Zn pairing.
- Electricity vs Iron: This process is called electrolysis. Write the chemical half-equation for the reaction occurring at the anode (oxidation of iron) and the reaction at the cathode (reduction of water).
- Electricity vs Iron: The green-brown substance that formed is iron(II) hydroxide, Fe(OH)₂. Explain how the products from the anode (Fe²⁺ ions) and the cathode (OH⁻ ions) combined to form this precipitate.
Answer Key
Worksheet Observations (Expected Results)
- Rust Protection: The plain iron nail and the iron nail with copper will show significant rusting (blue colour). The nail with zinc will show little to no rust on the iron; instead, a white, cloudy substance may form around the zinc wire as it corrodes. The zinc is the sacrificial anode.
- Electricity vs Iron: At the anode (+), the iron strip will visibly corrode and dissolve, and the solution around it will turn a greenish-brown colour. At the cathode (-), bubbles of gas (hydrogen) will form and stream off the iron strip.
Year 8 Research Questions
- The zinc blocks are more reactive than the steel hull. They rust (corrode) sacrificially, protecting the ship's hull from rusting away in the saltwater.
- Iron needs both oxygen and water to rust.
- Electricity can be used to split water into hydrogen gas and oxygen gas. This is called the electrolysis of water.
- Evidence could include: gas bubbles forming, a solid changing shape/dissolving, a new colour appearing in the solution, a new solid (precipitate) forming.
Year 9 Research Questions
- In the series, zinc is more reactive than iron, and iron is more reactive than copper (Order: Zn > Fe > Cu). Because zinc is more reactive, it will preferentially oxidize (lose electrons) before iron, thus protecting it. Copper is less reactive, so it does not protect the iron; in fact, it can accelerate the rusting of iron.
- Galvanic corrosion is an electrochemical process where one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte. In the Fe-Zn pairing, the more reactive zinc acted as the anode (site of oxidation) and the iron acted as the cathode (site of reduction/protection).
- Anode (Oxidation): Fe(s) → Fe²⁺(aq) + 2e⁻
Cathode (Reduction): 2H₂O(l) + 2e⁻ → H₂(g) + 2OH⁻(aq) - The oxidation at the anode produces aqueous iron(II) ions (Fe²⁺). The reduction of water at the cathode produces hydroxide ions (OH⁻). These ions move through the solution and combine in a precipitation reaction to form solid iron(II) hydroxide: Fe²⁺(aq) + 2OH⁻(aq) → Fe(OH)₂(s).