IChO 1990, Подбрани задачи 1980–1990 · семинар Амстердам 1990 — Задача 10. Practical problem No. 2 — Potentiometric determination of phosphoric acid in Coca-Cola
The best ICHO-tasks of the last years — Amsterdam workshop, October 1990 (selection from 1980–1990)
Внимание: Бележка към темата
This archive copy is the 1990 Amsterdam workshop top-twelve selection, containing eight theoretical tasks and four independent practical experiments from earlier Olympiads. 1990 identifies the workshop, not the year of every selected task. Solutions are attributed to the archive copy; no established official authorship is inferred. Practical1,2 and4 have no supplied keys. Separate report/answer forms referenced by Practical1,2 and3 are absent; Practical4 includes its blank answer sheet. Printed scientific and numerical discrepancies are retained.
Third International Workshop on the Development of the International Chemistry Olympiads (Amsterdam, October 1990)
According to the decision of the work shop of Amsterdam the delegation leaders of 8 countries made an attempt to rank the ICHO-tasks of the years 1980 ~ 1990 into the categories excellent / good / not so good / not acceptable The following pages indicate the ”top-twelve”, i.e. is the best tasks of the last years. This collection should be an aid for the ICHO-designers of the next years. Examples for tasks considered as ”not acceptable” are available for the next organisers too.
Original ranking tables (1980–1990)
The workshop’s complete native ranking tables are retained below. Ratings exc., good, n.s.g. and n.acc. are those printed by the source.
Условие
Apparatus: Round bottom flask (500 mL), magnetic stirrer, reflux condenser, water bath, electric heater.
Reagents: 6.0 g charcoal, standard solution of sodium hydroxide (c = 0.05 mol L⁻¹), buffer solutions.
Preparation of the sample: Pour the contents of a Cola can into a round-bottomed flask and add 6.0 g of powdered charcoal to the stirred solution. Cautiously raise the temperature of the solution and reflux for 10 minutes. Allow the solution to cool to room temperature and filter using a fluted filter paper. Repeat the filtration step.
Calibration of the potentiometer: Calibrate the pH-meter by means of two buffer solutions.
Titration: Titrate a 150 mL aliquot of your sample with sodium hydroxide solution (c = 0.05 mol L⁻¹) by measuring the pH using a pH-meter. The first equivalence point occurs after the addition of about 6 mL NaOH solution. Continue the titration until at least 12 mL of sodium hydroxide solution has been added.
Evaluation:
a) Draw the titration curve. Determine the first equivalence point.
b) Give the pH-value of the boiled Cola-beverage and the pH-value of the first equivalence point.
c) Calculate the concentration of phosphoric acid in the Cola-beverage. Record the calculation and the result in the answer sheet.
Решение
Внимание: Непълно решение
В архива няма официално решение на тази задача.
Оригинал в Архива: best_problems_1980-1990.pdf · допълнителни данни: IChO 21st-40th.pdf