SCIENCE · INVESTIGATE AND EXPLAIN

Balance electron equivalents separately from ionic charge

Combine half-reactions under a specified medium before calculating reaction yield.

Learning outcome: Compare Fe2+ feeds 10,15,25 at MnO4−2. Retain electron equivalents, acid consumption and residual amounts; audit charge and O/H atom counts in the combined equation.

Starting recap

Review amount dimensions, chemical formulas and charge, signed differences, ratio bounds and the distinction between a theoretical constraint and measured conversion.

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Try

Fifteen mmol Fe2+ with two mmol MnO4− permits extent 2 mmol, transferring10 mmol electron equivalents and leaving5 mmol Fe2+.

Open the experiment

Predict

Does a five-electron reduction imply five free electrons remain in the final solution?

Your prediction and reason

Experiment

Compare Fe2+ feeds 10,15,25 at MnO4−2. Retain electron equivalents, acid consumption and residual amounts; audit charge and O/H atom counts in the combined equation.

Match electron equivalents before a redox yield

Worked teaching model · synthetic values · Specified acidic aqueous model: MnO4− + 8H+ +5Fe2+ → Mn2+ +4H2O +5Fe3+. H+ is in stipulated excess; no other pathways. Oxidizing chemicals and acid are not handled. Electron count is a reaction-equivalent ledger, not free electrons accumulating in solution.

Fe2+ available: 15 mmol MnO4− available: 2 mmol

Reset keeps your prediction, captures and practice history.

MnO₄⁻ + 8 H⁺ + 5 Fe²⁺ → Mn²⁺ + 4 H₂O + 5 Fe³⁺

Stipulated acidic medium. Protons come from the declared excess reservoir; electron equivalents cancel between half-reactions and are not free product electrons.

Before, signed reaction change and after — theoretical packet, not actual measured conversion
Species	Initial	Change	Final	Unit
Fe²+	15	-10	5	mmol
MnO4−	2	-2	0	mmol
Fe³+	0	10	10	mmol
Mn²+	0	2	2	mmol

Calculated evidence under the stated assumptions
Quantity	Value	Unit
Reaction extent	2	mmol
Electron equivalents transferred	10	mmol electrons
H+ consumed from excess reservoir	16	mmol
Water formed	8	mmol
Left charge per reaction unit	17	e
Right charge per reaction unit	17	e

Five one-electron oxidations accompany one five-electron reduction.

Fe²+→Fe³++e− and MnO4−+8H++5e−→Mn²++4H2O cancel electrons when combined. Acidic medium and the specified products are essential; changing medium can change the manganese product and stoichiometry. This mathematical packet authorizes no oxidizer or acid handling.

Retain the reaction/measurement boundary with every number. This mathematical packet is not a chemical procedure or evidence of actual laboratory technique.

Five one-electron oxidations accompany one five-electron reduction.

Observation to attach to a capture

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

Separate oxidation state from net charge

Oxidation state is electron-assignment bookkeeping. In MnO4−, four oxygens assigned−2 require manganese+7 so the sum is −1. Producing Mn2+ lowers manganese’s assigned oxidation state by five. That change counts transferred electron equivalents; it does not say that the entire reactant ion initially has charge+7.

Build compatible half-reactions

The oxidation is Fe2+→Fe3++e−. In the specified acidic medium, reduction is MnO4−+8H++5e−→Mn2++4H2O. Multiplying the iron half-reaction by five and canceling electrons gives MnO4−+8H++5Fe2+→Mn2++4H2O+5Fe3+. Oxygen and hydrogen balance, and both sides have total charge+17 per symbolic reaction unit.

Use electron stoichiometry for amount inference

With 15 mmol Fe2+ and 2 mmol permanganate, extent is the smaller of 15/5 and 2, hence2 mmol. The model forms10 mmol Fe3+ and 2 mmol Mn2+, consumes16 mmol H+ from the stipulated excess reservoir and leaves5 mmol Fe2+. Ten mmol electron equivalents transfer between the half-reactions; they do not accumulate as free product electrons.

Preserve the medium boundary

The chosen reduction product and proton coefficient depend on the declared chemistry. Manganese can have different products under different conditions. A balanced equation for one medium cannot be used unchanged as a universal permanganate reaction. The activity supplies excess acid and complete conversion for mathematical analysis; it does not establish actual mechanism, kinetics or selectivity.

Transfer without a protocol

If10 mmol Fe2+ meets3 mmol MnO4− under the same assumptions, extent is 2 mmol and one mmol MnO4− remains. The limiting amount follows electron equivalents, not which feed has the smaller raw number. No acid, oxidizer or metal solution is handled in this lesson. The retained evidence is a symbolic balance and a virtual inventory, not a performed redox experiment.

Sources and evidence boundary

Conceptual sources checked 30 October 2026: Oxidation-reduction reactions. All prose, cases, code and diagrams are original. The supplied models are not measured structures, a performed laboratory investigation or certification of independent mastery. No chemical handling, heating, pressure vessel or cryogenic experiment is requested. Retain predictions, contrasting evidence and a changed-case explanation.

Apply

Public practice checks a specific claim. It does not establish independent mastery.

Why can changing the medium invalidate an otherwise balanced product assumption?

Your explanation and limitations

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Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

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Previous: Cancel spectators from an equation without deleting them from solution Next: Use reaction extent to explain a limiting-reactant switch

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