Connect reaction representations and evidence limits
Solve eight mixed reaction cases, diagnose competing explanations, and separate conserved ledgers from supported physical conclusions.
These original public packets sample connected Unit 4 reasoning. They are not a secure exam, unseen assignment, full-unit mastery score or a conducted practical. Existing Unit 1 and Unit 2 reviews retain separate counts and history.
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Separate balanced products from identified composition
Two proposals for C + O₂ → CO + CO₂ use coefficients 5:4:2:3 and 4:3:2:2 in that order. Choose the supported conclusion. Independently check carbon and oxygen and explain whether dividing by a common factor makes the two proposals identical.
Quantity / representation
Packet value
Proposal A
5 C + 4 O₂ → 2 CO + 3 CO₂
Proposal B
4 C + 3 O₂ → 2 CO + 2 CO₂
Missing evidence
No conditions, product analysis, rate or yield supplied
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0/3 attempts retained. No feedback exposure is recorded.
Cancel only an unchanged species portion
A supplied complete ionic inventory contains 7 X⁻(aq) before and 3 identical X⁻(aq) after. All other species are fixed, and the full equation is balanced. Enter the X⁻ coefficient remaining on the reactant side after maximal equal-term cancellation. Explain why the whole X⁻ species cannot be called a spectator solely because some remains.
Quantity / representation
Packet value
X⁻ before / after
7 /3, same composition, charge and state
Operation
Subtract equal identical terms from both sides
Interpretation
Cancellation changes the written difference, not the full physical inventory
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Preserve a weak molecular acid in the net equation
The packet supplies weak acid HNO₂(aq), a fully dissociated strong base and an acid–base reaction. Choose the appropriate stoichiometric net ionic representation. Check H/O/N and total charge, name the conjugate pair, and explain why this equation does not give an equilibrium composition.
Quantity / representation
Packet value
Acid premise
HNO₂ is weak; do not represent its entire initial amount as H⁺ + NO₂⁻
Base participant
OH⁻(aq)
Scope
One-proton stoichiometric representation, no equilibrium constant supplied
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Bound theoretical capacity without promising actual product
For the supplied reaction 3 A +2 B →2 P, allowed input amounts are A=12±3 mmol and B=10±2 mmol, with every pair of allowed values possible. Use stipulated M(P)=50 g/mol. Enter the lower bound of the theoretical product-mass ceiling in grams. Explain its upper bound, whether one reagent must always limit, and why this is not guaranteed collected product.
Quantity / representation
Packet value
Allowed amounts
A 9–15 mmol; B 8–12 mmol
Stoichiometry
3 A +2 B →2 P
Teaching molar mass / scope
P 50 g/mol; no actual conversion or recovery supplied
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Construct multipliers from a new pair of electron counts
An original oxidation half produces 4 electron equivalents and a reduction half consumes 3. Enter the electron equivalents canceled in the smallest positive whole-half combination. Give both multipliers in your explanation and describe what fails if one copy of each is combined then the unmatched electron is erased.
Quantity / representation
Packet value
Oxidation half
Produces 4 e⁻ per copy
Reduction half
Consumes 3 e⁻ per copy
Requirement
Both halves participate; no external electron source or sink
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Distinguish proton transfer from a globally conserved alternative
A supplied donor has charge −2 and transfers one H⁺ to a neutral acceptor. A proposed construction moves one H nucleus but leaves both charges unchanged. Which repair represents H⁺ transfer? Explain why the uncorrected construction can still conserve global atoms and charge.
Quantity / representation
Packet value
Parents
Donor charge −2; acceptor charge 0
Transferred entity
One H nucleus with charge +1 and zero electrons
Candidate mistake
H moved, both net charges unchanged
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Choose evidence that distinguishes a chemical change
An original observation packet reports bubbles when a colorless liquid is warmed. It gives no initial dissolved-gas inventory, gas identity or chemical analysis. Which conclusion and next-evidence plan are justified? Name a physical alternative and explain why a closed-system mass check alone would not distinguish it from a chemical reaction.
Quantity / representation
Packet value
Reported observation
Bubbles during warming
Missing controls
No matched warming blank, dissolved-gas baseline or product identification
Scope
Fictional observation record, not a conducted practical
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0/3 attempts retained. No feedback exposure is recorded.
Distinguish recovered target from isolate mass and conversion
A supplied theoretical target ceiling is 2.40 g. The recovered isolate has mass 2.10 g and an independently supplied target mass fraction 0.80. Enter the corrected target recovery as a percentage of the theoretical ceiling. Explain why neither isolate mass alone nor corrected recovery identifies reaction conversion when collection losses are unknown.
Quantity / representation
Packet value
Theoretical target ceiling
2.40 g
Isolate mass / target mass fraction
2.10 g /0.80
Unknowns
Incomplete conversion, side reactions and collection loss not separately measured
Write a reason before recording. This checks only that text is present, not its correctness. Your explanation stays editable and is not a locked first-attempt report.
0/3 attempts retained. No feedback exposure is recorded.
Retain a snapshot for a human review
The report separates current editable explanations from retained first/latest answers. It includes comparison reasoning only for already exposed cases. Preparing a snapshot does not submit it or establish independent review.
The observation packet asks what evidence is missing; it is not authentic empirical data or a conducted investigation. A human reviewer should request unfamiliar representations, inspect atom/charge and uncertainty reasoning, and assess practical evidence separately. These cases do not close empirical classification, independent half-reaction derivation, broader quantitative design or supervised practical requirements.
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