There are four factors that dictate the number of collisions and therefore the amount of successful reactions:
- Temperature
- Surface area
- Concentration
- The presence of a catalyst
Our experiment aims to show how temperature affects the rate of reaction while the other factors remain constant.
Equipment
Glass beakers (100ml and 250ml)
Measuring cylinders (10, 25, 100 and 250ml)
Test tubes and boiling tubes
Stirring rods
Thermometers
Stopwatches
Water baths (30°, 40°, 50°, 60°)
Hydrochloric acid (2moldm-3)
Sodium Thiosulphate (40g per litre)
Method
Pour 5ml of Hydrochloric acid and 30ml of water into a boiling tube/test tube. Pour 20ml of Sodium Thiosulphate into a separate tube. Draw a large cross on a piece of paper and place a beaker over it. Pour the contents of the 2 test tubes into the beaker at the same time; the process of pouring at the same time effectively stirs the reactants. Measure with a stopwatch the time between pouring the reactants into the beaker and the cross underneath the beaker being no longer visible. Record this time and wash out the beaker. For the different temperatures just do the same but before you pour the contents of the tubes into the beaker, put them both in the water bath. Wait until they reach the desired temperature (use a thermometer) and continue the experiment. Continue like this until you have a measurement for each temperature. It is recommended to have at least 2 measurements for each temperature though so carry out some retests and take an average time.
Fair Test
To make the experiment fair, only the temperature of the reactants will be changed. The other factors that determine rate – surface area, concentration & a catalyst – will remain constant. The same apparatus will be used for each experiment and will be washed out after each result is recorded.
Preliminary work
To decide which concentration of Sodium Thiosulphate to use we conducted some preliminary work. We decided to use 20ml of Sodium Thiosulphate and 30ml of water as it wasn’t too slow but would not be too quick on the higher temperatures.
Prediction
I predict that as the temperature increases by 10°C, the time will half and the rate will double. This is because as the temperature rises the molecules become more agitated, moving faster and colliding more with greater energy producing more successful reactions.
Safety
Sulphur dioxide gas is poisonous. As soon as the experiment is complete, the reaction mixture must be disposed of with lots of running water and the glassware is to be rinsed.
Eye protection must be worn when acid is being handled in the lab.
