Prac 3

Question 1

Required Practical 3
Rate of Reaction and Temperature

Answer 1

• Use a measuring cylinder to measure 10.0 cm3 of 0.05 mol dm3 sodium thiosulfate solution into a conical flask. Place this on a white tile with cross drawn in black ink.
• Note the initial temperature.
• Add 1 cm3 of hydrochloric acid to the thiosulfate solution and start timing.
• Record the time for the cross to disappear from view.
• Record the final temperature of the reaction mixture.
• Repeat (using water baths/ice) to obtain results for at least five different temperatures in total, ideally spaced 10°C apart.
• Plot a graph of temperature v time, using the average temperature for each reaction.

Question 2

Repeat using five different temperatures, spaced x?

Answer 2

10°C apart. Keep all other variables the same (control variables like volumes, flask, paper with the cross etc.).

Question 2

Why Record the time for the cross to disappear from view, why is it flawed, why does it disappear from view?

Answer 2

The practical is flawed because the disappearance of the cross is subjective (different people see different things). It won’t make a big difference but it is far better to use a light gate and data logger.
The cross disappears because solid yellow sulphur is produced (S(ppt)).

Question 3

Sometimes Rate vs Concentration is used. How to do this?

Answer 3

Change the concentration of one of the reactants. It is easier to dilute one of the reactants by reducing the volume of the reactant and making up to the original volume with deionised water.
Use five different concentrations, uniformly spaced apart. Keep all other variables the same (control variables like volumes, temperature, flask, paper with cross etc.).

Question 4

Why use a conical flask instead of a beaker?

Answer 4

Reduces loss of liquid droplets Allow description of reduction of loss of liquid

Question 5

Why can orders with respect to certain reactants be ignored?

Answer 5

Concentrations much larger than other reactants, or change in conc is neglibile.