I will first make my concentration of Sodium Thiosulphate. To do this I will mix Sodium Thiosulphate with Water. I have shown the concentrations above in the table. One I have my 25cm³ of concentrated Sodium Thiosulphate I will place it into a conical flask, which will be placed on top of a board with an X marked on it. I will then add 20 cm³ of Hydrochloric Acid. As Hydrochloric Acid is added I will start the stopwatch. When the letter X can no longer be seen the stopwatch will be stopped and the time will be recorded. The experiment is repeated with all the concentrations. The whole procedure is then repeated. I will repeat this until I find a concentration that takes a suitable amount of time. I will be looking for a time of around 90-100 seconds.
- 2nd Experiment - Changing The Temperature
I will first make a large amount of my concentrated Sodium Thiosulphate. The concentration I found in my preliminary experiment. To make my large amount of concentrated Sodium Thiosulphate I will take the amount of Sodium Thiosulphate that is appropriate for the concentration I am making and multiply the amount my 10. I will also do this for the amount of water. I have decided to do this so that I know that the concentration is always the same throughout the experiments, so if there is a slight mistake in the concentration every1 of my results will contain that mistake, therefore making it a fair test.
I will then measure out 25cm³ of concentrated Sodium Thiosulphate in a measuring cylinder and place in the conical flask. I will then heat to the desired temperature (20-70ºC increasing in 10ºC intervals) on the Bunsen burner. I will then place my conical flask on top of the board that is marked with an X and add 20 cm³ of Hydrochloric Acid. As the Hydrochloric Acid is added I will start the stopwatch. When the letter X can no longer be seen the stopwatch will be stopped and the time will be recorded. I will repeat this procedure for all other temperatures.
Repeat results and averages will be taken to improve the credibility of the findings, and present solid grounding for the final conclusion. The repeat results will help to iron out any anomalies that may occur and the average will give a good summary of the results of the experiment. However if one set of results is entirely different to the other, a third experiment will be performed to replace the anomalous set of results.
A pair of goggles will be worn throughout experiment in order to protect the eyes due to the corrosive nature of Hydrochloric Acid. This reaction will also produce a poisonous gas when in hailed in large amounts. So I will carry out this experiment in a well ventilated room. When handling hot beakers a pair of tongs will be used. A gauze and heatproof mat will be used while heating to avoid any damage to the equipment.
In order for my findings to be valid the experiment must be a fair one. I will use the same standard each time for judging when the X has disappeared. I will make sure that the measuring cylinders and beakers for the Hydrochloric Acid and Sodium Thiosulphate will not be mixed up. This can lead to contamination and incorrect results. The amount of Hydrochloric Acid will be fixed at 20 cm³ each time, and the amount of Sodium Thiosulphate will be fixed at 25 cm³. During the heating stage of the experiment, a blue flame will be used throughout. Also the same Bunsen burner and gas tap will be used to maintain continuity. All of these precautions will make my final results more reliable and keep anomalies at a minimum so thus make the entire investigation more successful.
Prediction
I predict that as the temperature is increased the rate of reaction will increase. I also predict that as the concentration of the Sodium Thiosulphate increases the rate of reaction will increase. This means that both graphs drawn up in my analysis will have positive correlation, and will probably be curved as the increase in rate of reaction will not be exactly the same as the concentration/temperature is increased.
This can be justified by relating to the collision theory. When the temperature is increased the particles will have more energy and thus move faster. Therefore they will collide more often and with more energy. Particles with more energy are more likely to overcome the activation energy barrier and thus react successfully. If solutions of reacting particles are made more concentrated there are more particles per unit volume, collisions between reacting particles are therefore more likely to occur. All this can be understood better with full understanding of the collision theory itself.
For a reaction to occur particles have to collide with each other. Only a small percent result in a reaction. This is due to the activation energy barrier. Only particles with enough energy to break past the barrier will react after colliding. The minimum energy that a particle must have to overcome the barrier is called the Activation Energy, or Ea. The size of this activation energy is different for different reactions. If the frequency of collisions is increased the rate of reaction will increase.
Maxwell-Boltzmann energy distribution curves show the distribution of the energy in a reaction.
The main points to note about the curves are:
- There are no particles with zero energy.
- The curve does not touch the x-axis at the higher end, because there will always be some
particles with very high energies.
- The area under the curve is equal to the total number of particles in the system.
- The peak of the curve indicates the most probable energy.
The activation energy for a given reaction can be marked on the distribution curve. Only particles with energy equal or greater than the activation energy can react when a collision occurs.
Increasing the temperature of a reaction affects the Maxwell-Boltzmann energy distribution curves. The theory is that for every 10ºC rise the rate of reaction will double. A small increase in temperature causes significant changes to the distribution energy.
As the temperature increases:
- The peak is at a higher energy.
- The peak is lower.
- The peak is broader.
- There is a large increase in the number of particles with higher energies.
It is the final change that results increase in rate, even with a relatively small increase in temperature. A small increase in temperature greatly increases the number of particles with energy greater than the activation energy. The shaded areas on the energy distribution curves show this.
