Tag: planning notes

Purpose of These Notes

These notes cover all five types of Planning questions tested in H2 Chemistry Paper 4: Volumetric Analysis (Titration), Gravimetric Analysis, Gas Collection, Energetics, and Kinetics. For each type, you will find: what the question is testing, the exact procedural format with precision-tagged steps, a worked example using the thermometric titration question from RVHS 2024, a mark scheme, and the most common errors.

The mark annotation system used throughout: (P1) = Procedure, (P2) = Precision, (A) = Apparatus, (R) = Reliability, (Q) = Quantity.

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1.2 General Rules That Apply to ALL Planning Questions
• Write your procedure in numbered steps — never continuous prose.
• Every step must name the apparatus and give the quantity to the correct precision.
• State both the initial and the final measurement for every instrument used.
• Reliability steps (repeat until consistent) must be specific — state the tolerance (e.g. ±0.10 cm³, ±0.01 g).
• Safety: name the specific chemical involved and the specific hazard it poses. Give the action to take, not the action to avoid.

⚠ Never repeat information already given in the question. Read the question stem carefully — restating given facts scores zero.

PART 2 — VOLUMETRIC ANALYSIS (TITRATION)

2.1 What is Tested

Titration questions ask you to determine an unknown concentration, basicity (number of acidic H⁺), or percentage purity. They may involve: acid-base titration, back titration, redox titration (MnO₄⁻ or iodometric), or thermometric titration. The planning always follows a three-phase structure: (i) preparation of standard solution, (ii) dilution if needed, (iii) the titration itself.

2.2  Pre-Experimental Calculation — Titre Volume

Before writing any procedure, check whether a dilution is needed. The key rule:

Key Rule

Target titre volume: 10.00 – 40.00 cm³. If concentrations differ by a factor of 10 or more, dilute first using C₁V₁ = C₂V₂. Use a 250 cm³ volumetric flask for dilution.

A titre that is too high → requires burette refill → high % error.

A titre that is too low → small volume → high % error from burette uncertainty (±0.05 cm³ per reading).

Percentage error in burette = (0.10 / titre volume) × 100%. Target ≤ 0.5%.

2.3  Indicator Selection

Choosing the wrong indicator is a common and costly error. Always match indicator to the type of titration.

2.4 The Standard Procedure — Step by Step

Phase 1: Preparation of Standard Solution (from solid)

1. Weigh accurately about [mass to 2 d.p.] g (P2), (Q) of [name of solid] into a dry and clean (R) weighing bottle (A), (P1).
2. Transfer the solid quantitatively into a 100 cm³ beaker (A). Reweigh the emptied weighing bottle and record its mass (P1). Calculate the actual mass transferred (P1).
3. Add from a 50.00 cm³ (P2) burette (A), [volume to 2 d.p.] cm³ (P2) of [solvent/acid] to dissolve the solid. Swirl until fully dissolved (R), (P1).
4. Transfer the solution and all washings into a 250 cm³ volumetric flask (A). Make up to the mark with deionised water (P1).
5. Stopper and shake the flask and mix thoroughly to obtain a homogeneous solution (P1).

⚠ Always reweigh the emptied weighing bottle — this gives the actual mass transferred. Do NOT weigh into the volumetric flask directly.

Phase 2: The Titration

6. Pipette 25.0 cm³ (P2), (Q) of [analyte solution] into a 250 cm³ conical flask (A), (P1).
7. Add 2–3 drops of indicator name into the conical flask.
8. Fill a 50.00 cm³ burette (A) with [titrant solution] and record the initial burette reading to 2 d.p. (P1), (P2).
9. Titrate [titrant] against [analyte]. Add dropwise near the endpoint. Swirl the flask continuously (R). Stop when the solution changes from [colour A] to [colour B] and the colour persists for 30 s (P1).
10. Record the final burette reading and calculate the titre (P1). Repeat until two titre values are consistent within ±0.10 cm³ (R). Use the mean of the consistent readings (P1).

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