Titration to calculate Mr (A level required practical) booklet

This booklet walks students through the full titration practical — from preparing a standard solution to calculating the relative formula mass of an unknown organic acid — with every step written out explicitly and the calculation broken into manageable chunks. It’s built to work as a live lesson companion, not just revision material, with EAL tip boxes that explain the language of practical chemistry (what “persists” means, why we rinse, how to read a meniscus) without dumbing down the science.

Topics covered:

• Indicator selection — comparing methyl orange and phenolphthalein (pH ranges, colour changes), choosing the right one for a strong acid–strong alkali titration
• Preparing a standard solution — weighing by difference, dissolving, transferring to a volumetric flask, rinsing, and making up to the mark
• The titration method — rinsing pipette and burette with the correct solutions, performing a rough titration, then accurate titrations until concordant results are obtained
• Recording results — burette readings to the nearest 0.05 cm³, results table with rough, titre 1–3, and mean titre
• Calculating Mr from titration data — moles of NaOH → moles of acid (using stoichiometry) → scaling up from 25.0 cm³ to 250 cm³ → Mr = mass/moles
• Identifying an unknown organic acid — matching the calculated Mr against succinic, fumaric, malic, and tartaric acid

Key features:

• Full equipment list at the top — students can check they have everything before starting, which avoids disruption mid-practical
• Safety precautions box covering goggles, lab coats, and NaOH handling — ticks the risk assessment box without taking up half the booklet
• EAL tip boxes at every critical point: what a standard solution actually is, why we rinse the beaker into the volumetric flask, how to read a burette at eye level, what “persists” means in context — these explain the practical vocabulary that native speakers take for granted
• Step-by-step calculation scaffold with blanks at each stage — students fill in the values rather than staring at a blank page, which models the working examiners want to see
• Distinction between rough and accurate titrations made explicit — including the technique of adding quickly until 2 cm³ before the rough titre, then switching to drop-by-drop
• Concordant titre guidance built in — only averaging values within 0.10 cm³, with a reminder not to include the rough
• Table of organic acids (succinic, fumaric, malic, tartaric) provided for identification — turns the calculation into a genuine problem-solving task where students match their Mr to the correct compound
• Gap-fill exercise reinforcing key terminology (standard solution, meniscus, titre, end point, concordant)
• Exam-style questions targeting common practical assessment points: white tile reasoning, rinsing rationale, not blowing out the pipette, improving mass accuracy
• Aligned to OCR Chemistry A (H432) practical skills and Module 3.2.1