What is the overall reaction studied in Core Practical 14?
BrO3⁻ + 5Br⁻ + 6H⁺ → 3Br2 + 3H2O, followed by C6H5OH + 3Br2 → C6H2Br3OH + 3HBr
What is the purpose of the phenol in this experiment?
Phenol reacts with the bromine produced, removing it from solution; the end of the reaction is detected when phenol is used up.
How is the end point of the reaction determined?
When phenol is exhausted, bromine is no longer removed and it bleaches the methyl red indicator; the disappearance of the indicator signals the end point.
How much phenol solution and bromide/bromate solution are used?
10.0 cm³ of phenol solution and 10.0 cm³ of bromide/bromate solution.
How many drops of methyl red indicator are added to the mixture?
Four drops.
How much sulfuric acid solution is used and where?
5.0 cm³ of sulfuric acid solution is pipetted into a separate boiling tube.
How is the reaction started?
Mix the contents of the two tubes by pouring rapidly from one tube into the other and back; start the stop clock immediately.
What is timed in this experiment?
The time taken for the methyl red indicator to disappear in the reaction mixture.
Why is the reaction repeated at different temperatures?
To measure how the reaction rate changes with temperature, allowing calculation of activation energy.
What is the role of methyl red indicator in this practical?
It signals the end point of the reaction by changing colour when bromine is no longer removed by phenol.
Why is it important that the boiling tubes reach the water bath temperature before mixing?
To ensure that the reaction starts at a known, controlled temperature for accurate timing.
How is the reaction mixture handled to ensure uniform mixing?
Pour the contents rapidly between the two tubes and then back to the empty tube to ensure complete mixing.
What kind of kinetic information can be obtained from this practical?
The rate of reaction at different temperatures, which allows calculation of the activation energy using the Arrhenius equation.
Which ions are reacting to produce bromine in this experiment?
Bromide ions (Br⁻) and bromate ions (BrO3⁻) in acidic conditions (H⁺).
Why is sulfuric acid added separately rather than with the phenol?
To control the timing of the reaction and avoid premature reaction before the temperature stabilizes.
How is the rate of reaction determined from the data collected?
By taking the reciprocal of the time taken for the colour change to occur (rate ∝ 1/time).
What practical considerations help ensure accuracy in timing the reaction?
Use a consistent water bath temperature, ensure rapid and uniform mixing, and start the stopwatch immediately when the tubes are combined.
What safety precautions should be observed in this practical?
Wear gloves and goggles; bromine is toxic, phenol is irritant, sulfuric acid is corrosive; handle hot water baths carefully.
