Titration Unknowns Virtual Lab: Vinegar, Juice and H₂O₂

Q: Does every student get the same answer?

No. Each New sample hides a fresh random value, so question 3 accepts the whole 40–60 g/dm³ range. Question 4 uses fixed numbers for a single marked answer.

Updated 2026-10-07

This titration unknowns virtual lab matches the AP Chemistry labs on the acid content of a drink and on hydrogen peroxide by redox titration. It also matches the AQA GCSE titration required practical, which ends with a concentration calculation. Each sample hides a new random concentration, so students can't copy an answer from a neighbor. They dilute the sample, do a rough titre and then accurate titres until two agree. Then they calculate the concentration and press Check. The simulation shows their percentage error and a worked solution.

Titration of unknowns – vinegar, juice and hydrogen peroxide

Curriculum links

AP Chemistry Unit 4: topic 4.6 Introduction to Titration (SPQ-4.B) and topic 4.9 Oxidation–Reduction Reactions. Also the AP Chemistry labs on the acid content of a beverage and on % hydrogen peroxide by permanganate titration.
AQA GCSE Chemistry 4.4.2.5 (titrations) and its titration required practical, including the calculation of an unknown concentration.

Simulic is not affiliated with or endorsed by the College Board or AQA.

Before the lab (5 min)

Ask students to commit to a prediction:

"You put 25.00 cm³ of undiluted vinegar (about 0.8 mol/dm³ ethanoic acid) in a flask and titrate it with 0.100 mol/dm³ NaOH from a 50 cm³ burette. What will happen?"

Many students expect a normal titre of about 20 cm³. Leave the question open until they try it.

Method in the simulation

Set Sample to Vinegar and Dilution to Undiluted. Fill the burette, take a sample and run the tap fully open. Watch the burette run down to 50 cm³ with no color change. That tests the prediction.
Set Dilution to Recommended (×10: 25.00 cm³ made up to 250.0 cm³).
Read the initial burette reading in the zoomed view, to 0.05 cm³. Open the tap fully for a rough titre, close it at the first pink, read the final reading and press Record.
Press Take sample. Open the tap until about 1 cm³ before the rough titre, then press +1 drop until the whole flask stays pale pink. Record. Repeat until two accurate titres are within 0.10 cm³.
Calculate the ethanoic acid content of the original vinegar in g/dm³, then press Check.
Repeat with Pharmacy H₂O₂ (×25, titrated with 0.0200 mol/dm³ KMnO₄, no indicator) and Fruit juice (×2, citric acid).

For younger students, tick Read burette for me.

Run	Final reading (cm³)	Initial reading (cm³)	Titre (cm³)	Concordant?
Rough
1
2
3

Expected results

Undiluted vinegar needs 167–248 cm³ of NaOH, so the burette always runs out first. Over 40 new samples of each type, the simulation gave:

Sample	Dilution	Titrant	Equivalence volume (cm³)	Hidden value
Vinegar	×10	NaOH 0.100 M	16.7–24.9	40–60 g/dm³ CH₃COOH
Fruit juice	×2	NaOH 0.100 M	11.7–27.3	6–14 g/dm³ citric acid
Pharmacy H₂O₂	×25	KMnO₄ 0.0200 M	14.1–19.0	2.40–3.30 %

A sample vinegar run: rough 18.25 cm³, then 18.20 and 18.30 cm³ (concordant), mean 18.25 cm³.

n(NaOH) = 0.100 × 0.01825 = 1.825 × 10⁻³ mol = n(CH₃COOH).
c in the flask = 1.825 × 10⁻³ ÷ 0.02500 = 0.0730 mol/dm³. Original = × 10 = 0.730 mol/dm³.
0.730 × 60.05 = 43.8 g/dm³. The simulation's true value was 43.6 g/dm³, an error of +0.5 %.

An H₂O₂ run gave 15.65 and 15.55 cm³ (mean 15.60 cm³), which works out to 2.65 %, matching the true value. The bottle says 3 %, but the hidden values run from 2.4 to 3.3 % because opened peroxide decomposes.

Questions for students

(Prediction, asked again after the lab) What happens when you titrate undiluted vinegar with a 50 cm³ burette?
Which is a control variable in the vinegar titration?
What is the ethanoic acid content of your vinegar sample, in g/dm³?
From given titration data, what is the % H₂O₂ in the bottle?
What happens to the answer if citric acid is treated as reacting 1 : 1 with NaOH, and why?

Answers for teachers: (1) The burette runs out first, because about 200 cm³ would be needed. (2) The volume of diluted vinegar pipetted, 25.00 cm³. (3) Every sample lies between 40 and 60 g/dm³, so answers from 38.5 to 62 are accepted. The sim's Check gives each student's own error. (4) 2.92 % (accept 2.89–2.95). (5) The answer comes out three times too large: citric acid is triprotic, so n(acid) = n(NaOH) ÷ 3.

Common misconceptions

"Weak acids need less alkali." Ethanoic acid still reacts 1 : 1 with NaOH. Strength changes the pH curve, not the moles.
"Forgetting the dilution factor is a small error." It makes the answer 10 times (vinegar) or 25 times (H₂O₂) too small.
"KMnO₄ needs an indicator." Permanganate is purple and Mn²⁺ is almost colorless, so the first permanent pale pink is the end point. Read the dark KMnO₄ at the top of the meniscus.

Extension

Dilution design: set vinegar to ×2 or ×25 and compare the titres. Which dilution keeps the titre in the 10–25 cm³ range, and why does a titre under 10 cm³ increase the percentage error?
Redox ratio: ask students to derive n(H₂O₂) = 5/2 × n(MnO₄⁻) from the half-equations before they titrate.

FAQ

Does every student get the same answer?

No. Each New sample hides a fresh random value, so question 3 accepts the whole 40–60 g/dm³ range. Question 4 uses fixed numbers for a single marked answer.

How accurate is the simulated equipment?

The burette reads to 0.05 cm³, one drop is about 0.05 cm³ and the pipette varies by about ±0.03 cm³. With careful drop-wise end points, students usually land within ±1 % of the true value.

Why does the juice end point come slightly early?

Citric acid's third proton is weak, so phenolphthalein turns pink about 0.5 % before the equivalence point. The model note in the simulation explains this.