Required Practical: Investigating the Effect of Concentration on Rate of Reaction Flashcards
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What two methods are used in the required practical investigating the effect of concentration on rate?
Measuring the volume of gas produced, and following a change in colour or turbidity (the disappearing cross).
What are the steps of the 'disappearing cross' method for investigating concentration and rate?
e.g. sodium thiosulfate + hydrochloric acid- Place the flask over a paper cross, add fixed volumes of thiosulfate and acid and start the timer.
- Time how long until the cross can no longer be seen through the cloudy mixture.
- Repeat with different concentrations of thiosulfate, keeping volumes and temperature the same.
In the sodium thiosulfate and hydrochloric acid reaction, why does the mixture become cloudy?
Sulfur is produced, which is an insoluble solid (a precipitate).
In the required practical on concentration and rate, what are the independent, dependent and one control variable?
Independent: concentration of the solution; dependent: volume of gas collected (or time taken); control: temperature (also volumes and mass of solid).
When collecting a gas from a conical flask, why must the stopper be inserted as quickly as possible?
To reduce the amount of gas that escapes before it can be collected.
When collecting gas over water from a reaction flask, what apparatus error must be avoided with the delivery tube?
The delivery tube must not be left in the reaction mixture (the acid) — it must lead into the collecting vessel.