How this bench works

This page is for learners who want to know how the bench works and its limits, and for lecturers checking what the tool claims. No sign-in is needed.

In plain words

Every task goes the same way:

Read. Read the burette at the bottom of the curved surface, to two decimal places, ending in 0 or 5.
Titrate. Open the tap for a stream, then add one drop at a time near the end. Stop at the first lasting change of colour.
Record. Write each reading in the results table. A recorded reading cannot be changed.
Work it out. Choose the titres that agree, find their average, and use it in the calculation.

A worked example

These numbers are only for this example. No task uses them.

HCl 0.200 mol dm⁻³ in the burette; 10.0 cm³ of sodium hydroxide in the flask, with an indicator.
Titration 1: initial reading 0.40, final reading 8.45, so 8.05 cm³ of acid was used.
Titration 2: initial reading 1.20, final reading 9.15, so 7.95 cm³.
The two agree, so average them: (8.05 + 7.95) ÷ 2 = 8.00 cm³.
Moles of acid: 0.200 × 8.00 ÷ 1000 = 0.00160 mol. HCl + NaOH → NaCl + H₂O is one to one, so the flask held 0.00160 mol of NaOH.
Concentration of NaOH: 0.00160 ÷ (10.0 ÷ 1000) = 0.160 mol dm⁻³.

Words you will see

The same words as the welcome, each with an everyday example.

Titration: Adding one solution to another, a little at a time, to find how much reacts.Example: Like adding sugar to tea a spoon at a time until it tastes right, and counting the spoons.
Burette: A long glass tube with a scale and a tap at the bottom. It lets out a measured volume of liquid.Example: Its scale reads down: 0 is at the top, and the numbers grow as liquid runs out.
Pipette and filler: A pipette measures one fixed volume of liquid. The filler is the rubber bulb that draws the liquid up.Example: Like a dropper that always holds the same amount. Never suck it up with your mouth.
Conical flask: A flask with a wide base and a narrow neck, so you can swirl it without spilling.Example: It stands on a white tile, so a change of colour is easy to see.
Portion: The fixed volume of solution measured into the flask with the pipette.Example: Like one cup of rice measured for each pot.
Indicator: A few drops of a dye whose colour depends on how acidic the solution is.Example: Like a tea that changes colour when you add lemon.
End point: The point where the indicator first changes colour for good, and you stop adding.Example: Like the moment the tea first tastes sweet.
Equivalence point: The point where the moles of acid added exactly match what the base in the flask needs.Example: Like a recipe that needs exactly as many eggs as cups of flour.
Titre, cm³: The volume of solution added from the burette: the final reading minus the initial reading.Example: In the example: 8.45 − 0.40 = 8.05 cm³.
Rough titration: A first titration done quickly, with the tap open for most of it.Example: Like a quick first try at a recipe, before the careful ones.
Concordant: Titres that agree closely, within a set amount.Example: Like two people weighing the same bag and getting almost the same weight.
Meniscus: The curved surface of a liquid in a narrow tube. You read the bottom of the curve.Example: Water in a clear straw curves down in the middle.
Concentration, mol dm⁻³: How many moles of a substance are in each cubic decimetre (one litre) of solution.Example: Like how many spoons of sugar are in each litre of a drink.
Standard solution: A solution whose concentration is known exactly.Example: Like a measuring cup you trust, used to check the others.

Help is always near

Tips: two short tips on every screen. Hide them, and turn them back on in Settings.
Show me how: a short guide to the bench on a sample titration, offered on each topic.
The ring: a coloured ring around the next thing to tap, with the same words under the task.
How it works: what the bench calculates, and what it leaves out.

Review status

Not yet reviewed by a lecturer. The status is unreviewed. Use this for practice only, not for marks. It prepares you for a real practical. It does not replace one.

Engine

titralab-ab-0.1.0

Exercise version

0.1.0

Topics ready

1, Read the glasswaretitra-lab.read-the-glassware
2, Your first titrationtitra-lab.first-titration
3, Find the unknowntitra-lab.find-the-unknown

What the bench calculates

Hydrochloric acid runs from the burette into a portion of sodium hydroxide in a conical flask, with methyl orange as the indicator. After every drop the bench works out the acid left in the flask from one charge balance, and the flask's colour comes from that. Every colour and every level you see comes from that calculation.

The burette holds 50.00 cm³, marked every 0.10 cm³, with 0 at the top. The numbers grow downwards.
A drop is 0.05 cm³. An open tap runs 0.10 cm³ for each step drawn on the screen, about ten a second. There is no half drop.
Readings are to the nearest 0.05 cm³, so they end in 0 or 5.
Methyl orange has four named colours, always written beside the flask: Yellow. Orange-yellow. Orange. Red. It changes between pH 3.1 and 4.4. The end point in these tasks is the first drop that is no longer yellow.
Your answers are checked against your own readings and titres, with exact fractions, not rounded numbers.

What it assumes

25 °C, with the water constant Kw = 1.0 × 10⁻¹⁴.
Ideal solutions: activity is ignored, and volumes add.
Mixing is instant and perfect after each addition. The indicator does not change the pH.
Glassware is exact: the pipette delivers 25.00 cm³ and the burette scale has no error.
There is no random scatter: careful titrations here agree exactly.

What it leaves out

Real titres scatter more, because hands and eyes vary.
A real flask flashes colour where a drop lands. This bench shows only the mixed flask.
Real solutions can be impure or old.

What a phone cannot teach

How a real tap feels in your fingers, and how to swirl a flask.
Judging a real colour change by eye, in real light.
Lab safety. Only a real lab, with a demonstrator, can teach that.

Safety in a real lab

Sodium hydroxide burns skin and eyes. In a real lab wear goggles, and always use a pipette filler. Never your mouth.
Wear goggles and a lab coat at all times.
If any splashes in your eye, rinse it with water for 15 minutes and tell your demonstrator at once.

Reference values

For checking the bench by hand. These two benches are the only ones shown: the hidden cases in topics 2 and 3 are chosen per attempt and are not listed here.

Hydrochloric acid into sodium hydroxide, methyl orange
Bench	Values
Topic 2, task 1, Your first titration	HCl 0.100 mol dm⁻³ in the burette; 25.00 cm³ of NaOH 0.0950 mol dm⁻³ in the flask. The moles match at 23.75 cm³ of acid. The flask first stops being yellow at 23.80 cm³ of acid: Orange-yellow.
Show me how, the sample bench	HCl 0.120 mol dm⁻³ in the burette; 25.00 cm³ of NaOH 0.150 mol dm⁻³ in the flask. The moles match at 31.25 cm³ of acid. The flask first stops being yellow at 31.30 cm³ of acid: Orange-yellow.

How we check the numbers

Reference values were worked out first by a separate program, with 60-digit arithmetic, and the bench is tested against them.
Random titrations are tested for charge balance, and for colours and levels that move only one way.
The same results come out in Chrome, in Safari's engine and in Node, to the last digit.
These are engineering checks. They do not replace review by a qualified lecturer.

Tips

Nothing on this page is needed to do a task. Come back when you want to know why.
The words list is the same one the welcome shows. Settings opens the welcome again.

Your data

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