Acids, Bases & Titration — Extension · Physical Science: Chemistry, Grade 11
Separate strength from concentration and connect proton transfer with pH, buffers, and titration.
Reading a Titration Curve
Investigate
How well does a curve identify equivalence and unknown concentration?
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
- Provided titration data,calculator
- No acid handling required
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
Titrate 25.0 mL modeled HCl with.100M NaOH; infer equivalence from pH versus added volume.
Method
- Write a prediction and the physical/chemical mechanism behind it.
- Draw the setup or system boundary; label variables and units.
- Graph pH against added volume and locate the steepest interval.
- Use modeled equivalence 25.0 mL to infer acid amount and concentration.
- Discuss endpoint resolution and contrast a weak-acid curve.
- 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.
| NaOH volume(mL) | pH |
|---|---|
| 0 | 1 |
| 20 | 1.95 |
| 24.9 | 3.7 |
| 25 | 7 |
| 25.1 | 10.3 |
| 30 | 11.96 |
Analyze and explain
- Find acid molarity under 1:1 stoichiometry.
- Why is endpoint not identical to equivalence?
- Would a weak-acid equivalence necessarily be 7?
- 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
Equivalence 25.0 mL gives.00250 mol acid in.0250L, hence.100M. Endpoint is an observed signal with possible overshoot; equivalence is a stoichiometric condition. A weak-acid/strong-base titration commonly has basic equivalence due to conjugate-base hydrolysis. 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
Equivalence 25.0 mL gives.00250 mol acid in.0250L, hence.100M. Endpoint is an observed signal with possible overshoot; equivalence is a stoichiometric condition. A weak-acid/strong-base titration commonly has basic equivalence due to conjugate-base hydrolysis. 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
Equivalence 25.0 mL gives.00250 mol acid in.0250L, hence.100M. Endpoint is an observed signal with possible overshoot; equivalence is a stoichiometric condition. A weak-acid/strong-base titration commonly has basic equivalence due to conjugate-base hydrolysis. 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
Equivalence 25.0 mL gives.00250 mol acid in.0250L, hence.100M. Endpoint is an observed signal with possible overshoot; equivalence is a stoichiometric condition. A weak-acid/strong-base titration commonly has basic equivalence due to conjugate-base hydrolysis. 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
Equivalence 25.0 mL gives.00250 mol acid in.0250L, hence.100M. Endpoint is an observed signal with possible overshoot; equivalence is a stoichiometric condition. A weak-acid/strong-base titration commonly has basic equivalence due to conjugate-base hydrolysis. 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
Equivalence 25.0 mL gives.00250 mol acid in.0250L, hence.100M. Endpoint is an observed signal with possible overshoot; equivalence is a stoichiometric condition. A weak-acid/strong-base titration commonly has basic equivalence due to conjugate-base hydrolysis. 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
Equivalence 25.0 mL gives.00250 mol acid in.0250L, hence.100M. Endpoint is an observed signal with possible overshoot; equivalence is a stoichiometric condition. A weak-acid/strong-base titration commonly has basic equivalence due to conjugate-base hydrolysis. 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.