Increasing the temperature of the atoms taking part makes them move more and faster, enabling more collisions to take place, speeding up the reaction. The added heat energy also allows more collisions to have the required activation energy, again, speeding up the reaction.
In order to make this experiment a fair test, I changed only one input variable, the temperature. I kept the amount and concentration of the liquids the same (20ml of Sodium Thiosulfate, 5ml of HCl), so that this did not affect the results. I used the same indicator of clouding, a cross, drawn on a piece of paper underneath the conical flash. This was protected from the liquids, which would have made the ink run between experiments, making for inconsistent readings, by a plastic wallet. The same sized conical flask was used for all of the experiments as well, as different sizes or shapes may alter the speed of the reaction.
20ml of Sodium Thiosulfate, measured using a measuring cylinder, was added into a conical flask, and heated to the required temperature using a water bath heated by a Bunsen burner. A thermometer was used to monitor the Sodium Thiosulfate’s temperature, so that the flask could be removed from the water bath when the chemical was at the correct temperature. 5ml of HCl was measured in a different measuring cylinder, and was poured into the Sodium Thiosulfate when this was at the required temperature. The stopwatch was started when the acid had been completely poured in. Then, standing over the flask, which had been placed on top of the cross, I looked down, and stopped the watch when I could no longer see the meeting point of the two lines. This was carried out for each of the five temperatures. When the Sodium Thiosulfate had been heated too much, it was run underneath the cold-water tap to cool down.
I chose to use temperatures between 20°C and 40°C, as I felt that if I used higher temperatures, it would prove difficult in moving the hot equipment
List of Equipment
Bunsen Burner
Heatproof Mat
Tripod
200ml Beaker
100ml Conical Flask
2 50ml Measuring Cylinders
Thermometer
Digital Stopwatch
The results I obtained from the stopwatch recorded the time taken, in seconds to two decimal places, for the solution to cloud. As I felt that I could not be accurate to a hundredth of a second, I rounded the times to the nearest second. By looking at the results in the above table, I can see that there is agreement between all sets of results, with only a few seconds difference between two sets of results. The agreement shows that these results are accurate, and that the experiment does not need to be repeated.
I shall now plot the average of these results onto a graph, and shall draw a line of best fit.
By looking at the line of best fit on the graph, I can see that as the temperature that the reaction took place at increased, the time taken for the cross to be obscured decreased. The line of best fit is straight, so this shows that the relationship is inversely proportional.
The results found can be explained by the collision theory. As the temperature increased, the particles in the liquids gain energy, and vibrate more and further. The particles collide more often due to this, increasing the speed of the reaction. The vibrations carry more energy, so that when a collision takes place, there is more energy involved, meaning that more collisions have the required activation energy, again, increasing the speed of the reaction.
My method could have been improved in several ways. The amount of the chemicals used could have been made more exact by using a pipette, which is much more accurate than a measuring cylinder. A better method of timing the time taken for the solution to cloud could have been used, as my reaction times in observing the clouding, registering it, and stopping the stopwatch would have added extra time to the results. My method must have been quite appropriate, however, as the results that came out of it were very good, with agreement between the sets.