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CookbookLabs and workshopsNo. 24

A chemistry lab manualexperiments, hazards and a titration curve to play with

Recipe No. 24 · Labs and workshops

For: A chemistry teacher writing a year of lab practicals

You get: A manual of experiments, each hazard a Risk, and a titration to drive

Time: An evening to draft, a week to check

See it in know.sh

Try it. A titration you can run: choose the acid, add sodium hydroxide a drop at a time, and watch the pH curve jump at equivalence.

The vinegar titration: pre-lab, a Risk section per hazard, a section per step, a common mistake filed as a Problem, and the answer key kept off the link.

know., Experiment 7 · Look up, New, ⋯

Chemistry practicals, No. 7

Experiment 7 — How much acid is in vinegar?

11 sections, 2,140 words, about 9 minutes, filed 18 August, revised 22 September, 4 highlights.

☆ Star, Focus, Share, Move, Edit

Students titrate diluted white vinegar with 0.100 mol/L sodium hydroxide, using phenolphthalein, and work out how much ethanoic acid the bottle holds. It is the first titration of the year, so the pre-lab spends time on the burette and on reading a meniscus, and the model in the pre-lab shows why phenolphthalein is the indicator for a weak acid.

Two periods: the dilution and a rough titration in the first, three accurate titrations in the second. Concordant titres agree within 0.10 mL.

Sections

  1. Pre-lab: what a titration measures (Question, 4 questions). Equivalence, end point, titre and concordant results, then the model: add sodium hydroxide and watch where the pH jumps.
  2. Hazard: sodium hydroxide, 0.100 mol/L (Risk, key). Can damage eyes even this dilute. Goggles on before the bottle opens; control measures and first aid as in the school’s risk assessment. (highlighted)
  3. Hazard: phenolphthalein indicator solution (Risk, key). Made up in ethanol, which is flammable: no flames on the bench. Dropping bottles only, kept by the technician.
  4. Dilute the vinegar ten times. 25.00 mL by pipette, with a pipette filler, into a 250 mL volumetric flask; made up to the mark with distilled water and inverted to mix.
  5. Rinse and fill the burette. Rinse with a little of the sodium hydroxide, fill with a funnel with the burette below eye level, then take the funnel out before reading it.
  6. Titrate to the first permanent pink. Swirl constantly; drop by drop within a millilitre of the rough titre. The end point is the first pink that lasts thirty seconds.
  7. Reading the meniscus from above (Problem, 1 note). Read the bottom of the meniscus at eye level, to the nearest 0.05 mL. Two groups read from above last year and lost 0.2 mL.
  8. Data table and calculations: answer key (Evidence, key). Trial-run readings, a mean titre of 20.53 mL, and 4.93 g of ethanoic acid per 100 mL of vinegar. Left out of the link. (highlighted)
  9. Post-lab questions (Question, 5 questions). Why rinse the burette with sodium hydroxide? Why is methyl orange no use here? Read the pH at half-equivalence from the curve.

and 2 more sections

The answer key: trial-run readings as a table element with the concordant titres noted, then the calculation line by line.

Chemistry practicalsExperiment 7

8of 11

Data table and calculationsanswer key

Evidence, key section, 2 highlights, 1 note, 286 words

My trial run, 15 September, with the same stock the class will use: 0.100 mol/L sodium hydroxide, standardised by the technician that morning.

Sodium hydroxide used. 0.100 mol/L × 0.02053 L = 2.053 × 10⁻³ mol.

Ethanoic acid in the aliquot. CH₃COOH + NaOH → CH₃COONa + H₂O, one to one, so 2.053 × 10⁻³ mol in 25.00 mL.

Concentration. 2.053 × 10⁻³ mol ÷ 0.02500 L = 0.0821 mol/L in the diluted vinegar, so 0.821 mol/L in the bottle.

Mass per 100 mL. 0.821 mol/L × 60.05 g/mol = 49.3 g/L, which is 4.93 g per 100 mL, close to the 5 per cent on the label.

How it works

Replace the photocopied worksheets with a lab manual that improves every year. Each experiment has the same six parts, and each hazard is a Risk section written from your own risk assessment. Beside the titration sits a model: add sodium hydroxide a drop at a time and watch the pH curve climb, jump and level off.

  1. Draft the experiments from last year’s sheets

    Give your assistant last year’s sheets and your risk assessments. Ask for a document per experiment in six parts, a section per procedure step, and a Risk section per hazard.

  2. Check every hazard against the risk assessment

    Read each Risk section beside the risk assessment and the safety data sheet. Where they disagree, the risk assessment wins. Mark every hazard Key.

  3. Ask for a titration curve to play with

    Ask for a widget element in the pre-lab: pick the acid, add sodium hydroxide, watch the pH. Check it reads 4.76 at half-equivalence for ethanoic acid.

  4. Share each experiment, answers left out

    Share each experiment with the class, leaving the answer key out of the link. After each practical, have your assistant file what went wrong as Problem sections.

Try this prompt

Your assistant, connected to know.sh (Claude, ChatGPT or a local model):

In the Pre-lab section of Experiment 7 in my know.sh library, add a widget element: an acid–base titration model. Let the reader choose hydrochloric or ethanoic acid (pKa 4.76) and the concentrations, add sodium hydroxide with a slider and a one-drop button, and plot pH against volume with the equivalence and half-equivalence points marked. Suggest an indicator, and say in the caption what the model leaves out.

Your assistant, connected to know.sh (Claude, ChatGPT or a local model):

Using know.sh, make a shelf called Chemistry practicals and a document per lab sheet I have given you, titled “Experiment N — the question it answers”, with six sections: Pre-lab, Safety, Procedure, Data table, Calculations, Post-lab questions. Make each hazard a Risk section, taken only from my risk assessments, and file a Question wherever a figure is missing.

Made with

ShelfDocumentSectionYour AI assistantElementsPublic link

See also