Reactions, Moles & Composition — Extension · Physical Science: Chemistry, Grade 11
Account for atoms, charge, particle counts, and measured composition.
Atom Accounting and Ionic Change
Investigate
How do balanced equations conserve atoms and charge?
Use two dedicated sessions: first define the model, boundary, variables and comparison, then collect suitable records or analyze the complete supplied-data route; second complete calculations/graphs, compare alternatives, revise and prepare the report. Extend collection time where needed. Supplied-data work does not certify supervised laboratory minutes or mandated investigations.
Materials
- Colored paper counters
- Three paper ion cards Na⁺,Cl⁻,Ag⁺ and nitrate cards
Before you begin
Use only the listed household materials or analyze the supplied data. An adult should review setup. No flames, strong acids/alkalis, unknown chemicals, household mains, radiation sources, or high-speed projectiles are needed. Keep food-study materials separate from eating and wash hands afterward.
Plan a fair test
Count atoms/ions with a closed paper model; distinguish spectators from reacting ions.
Method
- Write a prediction and the physical/chemical mechanism behind it.
- Draw the setup or system boundary; label variables and units.
- Model 2H₂+O₂→2H₂O using counters and count each element.
- Write molecular and net ionic equations for the supplied silver-chloride reaction.
- Represent an empirical-formula result using mole counts, not raw masses.
- Record repeated observations where possible; keep original readings and note resolution or uncertainty.
- Write a claim supported by specific numbers, explain the mechanism, and identify one limitation and a next test.
Example data — for analysis when materials are unavailable
Illustrative teaching data, not measurements from a real district laboratory. Analyze these when materials are unavailable and identify them as provided data. Do not claim to have performed a measurement you did not make.
| Case | Initial count/amount | Product count/amount | Check |
|---|---|---|---|
| Water reaction | 4H,2O | 4H,2O | Atoms conserved |
| AgCl net | Ag⁺+Cl⁻ | AgCl | Charge 0 each side |
| Empirical sample | 1molC,2molO | CO₂ ratio | 1:2 |
Analyze and explain
- Why do coefficients change while subscripts stay fixed?
- Which ions are spectators?
- Why do elemental masses need conversion before ratio comparison?
- Link the pattern to a labeled particle, structure, energy or amount model from the chapter.
- Distinguish supplied illustrative records from measurements actually collected.
- Identify uncertainty and propose a comparison that would test an alternative explanation.
What a strong explanation includes
- A stated prediction, conditions, and controlled variables or explicit model boundary.
- A labeled table/graph with units, calculations, and attention to repeated values or uncertainty.
- A claim citing numerical evidence and a scientifically accurate mechanism.
- A limitation, alternative explanation, and useful follow-up test.
- Preserve initial reasoning and an evidence-supported revision.
- Check units, species identity, system boundary and physical assumptions.
Parent / teacher guide: discuss after the investigation
Coefficients count unchanged chemical formulas; modifying subscripts changes identity. Na⁺ andNO₃⁻ are spectators in the stated reaction. Mass-to-mole conversion accounts for different elemental molar masses before deriving atom ratios. Preserve the original observations, intermediate working and a labeled mechanism. Report the relevant boundary and model assumptions, discuss an alternative explanation, and identify the next useful measurement; do not replace unexpected data with the illustrative record.
Compare this model with the learner’s actual evidence. Different measurements can support a different conclusion; check the reasoning and limitations, not matching wording.
Extend the chapter investigation by evaluating its evidence and proposing a better test.
Problem 1
Answer and explanation
Coefficients count unchanged chemical formulas; modifying subscripts changes identity. Na⁺ andNO₃⁻ are spectators in the stated reaction. Mass-to-mole conversion accounts for different elemental molar masses before deriving atom ratios. Preserve the original observations, intermediate working and a labeled mechanism. Report the relevant boundary and model assumptions, discuss an alternative explanation, and identify the next useful measurement; do not replace unexpected data with the illustrative record.
Problem 2
Answer and explanation
Coefficients count unchanged chemical formulas; modifying subscripts changes identity. Na⁺ andNO₃⁻ are spectators in the stated reaction. Mass-to-mole conversion accounts for different elemental molar masses before deriving atom ratios. Preserve the original observations, intermediate working and a labeled mechanism. Report the relevant boundary and model assumptions, discuss an alternative explanation, and identify the next useful measurement; do not replace unexpected data with the illustrative record.
Problem 3
Answer and explanation
Coefficients count unchanged chemical formulas; modifying subscripts changes identity. Na⁺ andNO₃⁻ are spectators in the stated reaction. Mass-to-mole conversion accounts for different elemental molar masses before deriving atom ratios. Preserve the original observations, intermediate working and a labeled mechanism. Report the relevant boundary and model assumptions, discuss an alternative explanation, and identify the next useful measurement; do not replace unexpected data with the illustrative record.
Problem 4
Answer and explanation
Coefficients count unchanged chemical formulas; modifying subscripts changes identity. Na⁺ andNO₃⁻ are spectators in the stated reaction. Mass-to-mole conversion accounts for different elemental molar masses before deriving atom ratios. Preserve the original observations, intermediate working and a labeled mechanism. Report the relevant boundary and model assumptions, discuss an alternative explanation, and identify the next useful measurement; do not replace unexpected data with the illustrative record.
Problem 5
Answer and explanation
Coefficients count unchanged chemical formulas; modifying subscripts changes identity. Na⁺ andNO₃⁻ are spectators in the stated reaction. Mass-to-mole conversion accounts for different elemental molar masses before deriving atom ratios. Preserve the original observations, intermediate working and a labeled mechanism. Report the relevant boundary and model assumptions, discuss an alternative explanation, and identify the next useful measurement; do not replace unexpected data with the illustrative record.
Problem 6
Answer and explanation
Coefficients count unchanged chemical formulas; modifying subscripts changes identity. Na⁺ andNO₃⁻ are spectators in the stated reaction. Mass-to-mole conversion accounts for different elemental molar masses before deriving atom ratios. Preserve the original observations, intermediate working and a labeled mechanism. Report the relevant boundary and model assumptions, discuss an alternative explanation, and identify the next useful measurement; do not replace unexpected data with the illustrative record.