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A titration uses a burette to add variable volumes accurately, a pipette for a fixed volume (usually 25.0 cm³), a conical flask and an indicator. Free notes.
Core practical: acid-alkali titration is part of Using concentrations of solutions in mol/dm 3 (chemistry only) (HT only) in GCSE Edexcel Higher Chemistry.
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GCSE Edexcel Higher
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A titration uses a burette to add variable volumes accurately, a pipette for a fixed volume (usually 25.0 cm³), a conical flask and an indicator. Free notes.
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Use this lesson to stay inside Using concentrations of solutions in mol/dm 3 (chemistry only) (HT only) while connecting the detail back to the wider Topic 5: Separate chemistry 1 topic.
Read the core explanations from Core practical: acid-alkali titration before testing yourself from memory.
Picture this: you're given a bottle of hydrochloric acid, but the label has fallen off. You know it's HCl, but you don't know how concentrated it is. Is it strong enough to clean metal, or weak enough to add to food? This is where titrations save the day.
A titration is like a chemical detective story. You add a solution of known concentration (the standard solution) drop by drop to your mystery solution until they react completely. The moment this happens, an indicator changes colour - that's your clue that the reaction is finished.
Every titration needs five key pieces of equipment, and each has a specific job. Think of them as your chemical toolkit - miss one piece and the whole investigation falls apart.
The conical flask holds your unknown solution plus indicator. Why conical? The shape means you can swirl without splashing, and the narrow neck concentrates the colour change so you can spot the endpoint clearly.
Indicators are like chemical traffic lights - they change colour to tell you when to stop adding solution. For strong acid-strong alkali titrations, you have two main choices, and picking the right one matters for accuracy.
Methyl orange works brilliantly for strong acid-strong alkali titrations. It's red in acid and yellow in alkali, with a sharp colour change at the endpoint. Phenolphthalein is colourless in acid and pink in alkali - also sharp and reliable.
Universal indicator might seem like the obvious choice, but it's actually terrible for titrations. Why? It changes through multiple colours gradually, making it impossible to spot the exact endpoint. You need a sharp, sudden change.
Here's where theory meets practice. Follow this method exactly and you'll get reliable, accurate results every time. Miss a step and your results will be all over the place.
Worked example: Carrying Out an Acid-Alkali Titration
Find the concentration of sodium hydroxide solution using 0.100 mol/dm³ hydrochloric acid
Answer: Repeat until you get concordant results (within 0.10 cm³ of each other)
The whole point of doing a titration is to find an unknown concentration. This is where your careful practical work pays off - you can now use your titre values to calculate exactly how concentrated your mystery solution is.
Worked example: Calculating Unknown Concentration
25.0 cm³ of NaOH solution was neutralised by 23.5 cm³ of 0.100 mol/dm³ HCl. Find the concentration of NaOH.
Answer: Concentration of NaOH = 0.094 mol/dm³
Mark-winning tip: Always show the balanced equation first - it's usually worth a mark on its own. Then show each calculation step clearly with units throughout.
Titration questions are mark-rich in exams, but they're also where students lose clear and systematic marks through sloppy technique. Here's how to nail every mark available.
For 6-mark 'describe the method' questions, structure your answer like this: 1) Equipment setup and rinsing, 2) Measuring solutions accurately, 3) Adding indicator, 4) Carrying out the titration, 5) Recording results, 6) Repeating for reliability.
Common exam trap: Questions often ask why you rinse the burette with the acid solution. The answer is to remove water that would dilute the acid and make the concentration lower than expected. Don't say 'to clean it' - that's not specific enough for the mark.
A titre is the volume delivered from the burette, found by subtracting the initial burette reading from the final burette reading. Concordant titres are usually within 0.10 cm3 of each other. If one result lies outside that range, it should be treated as anomalous and left out of the mean. Students should also remember that either acid or alkali can be in the burette depending on the question setup.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
A titration uses a burette, a long graduated glass tube with a tap that delivers variable volumes accurately (±0.05 cm³), a pipette that delivers a fixed volume (usually 25.0 cm³), a conical flask for the unknown solution and an indicator.
A burette is a long, graduated glass tube with a tap at the bottom, used to deliver variable volumes of solution with high accuracy. A pipette delivers a fixed, accurate volume of solution, usually 25.0 cm³ in GCSE titrations.
Read the burette to the nearest 0.05 cm³, always at eye level to avoid parallax error. Record the initial and final readings, and calculate the titre = final reading - initial reading.
The endpoint is the point in a titration where the indicator changes colour permanently, showing that the acid and alkali have reacted completely in stoichiometric proportions. With methyl orange, the solution changes from red to yellow.
A conical flask is used in a titration because its shape allows the solution to be swirled without splashing. Its narrow neck also concentrates the colour change, making the end point easy to spot.
The pipette is rinsed with the alkali it will measure, just as the burette is rinsed with the acid, to remove water that would dilute the solution. Diluting it would make the concentration lower than expected.
Only 2-3 drops of indicator, such as methyl orange, are added because too much indicator affects the end point. The indicator only needs to show a sharp, permanent colour change.
An anomalous titre, one that lies outside the concordant range of 0.10 cm³, should be left out of the mean. The titration is repeated until there are concordant results.
Either the acid or the alkali can be in the burette, depending on the question setup. The other solution is measured into the conical flask with a pipette.