A control group in a scientific experiment is a group separated from the rest of the experiment, where the independent variable being tested cannot influence the results. This isolates the independent variable's effects on the experiment and can help rule out alternative explanations of the experimental results.
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Answer:
Explanation:
Oxygen gas and water must be present for iron to rust.
A region of the metal’s surface serves as the anode, where oxidation
occurs:
Fe(s) → Fe²⁺ (aq) + 2 e⁻
The electrons given up by iron reduce atmospheric oxygen to water at the cathode, which is another region of the same metal’s surface:
O₂ (g) + 4H⁺ (aq) + 4 e⁻ → 2 H₂O (l)
The overall redox reaction is:
2 Fe(s) + O₂(g) → 4H⁺(aq) + 2Fe²⁺ (aq) + 2 H₂O(l)
The Fe²⁺ ions formed at the anode are further oxidized by oxygen:
4 Fe²⁺ (aq) + O₂(g) 1 (4 + 2x) H₂O (l) → 2 Fe₂O₃ . xH₂O(s) + 8 H⁺(aq)
This hydrated form of iron(III) oxide is known as rust. The amount of water associated with the iron oxide varies, so we represent the formula as 2 Fe₂O₃ . xH₂O.
