The range of concentrations of hydrochloric acid I will use will be 0.2M, 0.4M, 0.6M, 0.8M and 1M and the measurements I take will be the time between when the acid is added, and when the cross is no longer visible for the solution. I chose this range, as the highest concentration of acid available to me is 1M. Therefore, I have to mix my other concentrations by diluting the acid with distilled water. Also, the range I have chosen will give me a good range of results.
To mix the different concentrations, I will add distilled water to the hydrochloric acid in the ratio to make the desired concentration. All volumes will be measured using a burette as after doing my preliminary work with measuring cylinders, I think it will make the test fairer if I use burettes as the will give more accurate readings.
This table shows the volumes of each solution needed to make the various concentrations:
Initial Equipment:
Stop clock
Paper with black cross drawn on
100cm3 Conical Flask
100cm3 Measuring Cylinder
Thermometer
Distilled Water
Sodium Thiosulphate 0.1M
Hydrochloric Acid 1M
Using the CD-ROM Focus on Science to research the experiment, I have decided to use a burette as opposed to a measuring cylinder to measure volumes. This will help me gain more accurate measurements. I chose the burette over the bulb pipette, as I will be measuring small volumes, and I feel the burette will enable me to do this most accurately.
Fair Test:
In order to ensure a fair test is carried out the concentration of the hydrochloric acid must be the only variable that is changed. The collision theory states that the more kinetic energy particles have, or the more particles there are in a solution, the more chance there is of a collision, and therefore the reaction is sped up. Particles must collide with sufficient force to react. Particles gain kinetic energy as they gain heat, and therefore the experiment must be carried out at the same temperature in order to ensure fair results are obtained. To do this, I will measure the temperature in the laboratory, to ensure there are no great changes in temperature. The concentrations of the chemicals will also affect the reaction speed, as there are more particles on the solution, there is a greater chance that they will collide. This means I must change only the concentration of the hydrochloric acid; the concentration of the sodium thiosulphate must remain the same.
Measurements should be taken accurately with a burette to maintain the same volumes of chemicals for each experiment.
Repeat the test twice to collect many results: this will highlight any irregularities.
Safety:
The chemicals used in this experiment can be harmful and should be treated with caution. Safety goggles must be worn at all times while near to or handling chemicals. If chemicals are spilt they should be wiped up immediately, and a teacher should be notified. Similarly, if chemicals are spilt on the skin, wash off immediately and alert a teacher. Do not contaminate chemicals by using the same pipette or other measuring device for both chemicals without washing them thoroughly. This will result in a large waste of chemicals.
Treat glass containers with care. If smashed, inform a teacher and stand well clear from glass. Follow all laboratory rules to avoid accidents. For example, do not run and do not eat in labs.
Prediction:
I predict that as the concentration of the acid increases, the reaction will occur more quickly. This is due to the collision theory, which states that as concentration increases, so does the amount of particles in the solution, which means there is a greater chance of a collision with a force that is sufficient to result in a reaction, therefore increasing the rate of reaction.
Results:
To make the results I collected as precise as possible, I used the most accurate equipment I could and used great care when taking results and measuring. Measurements were taken with a burette to ensure the same volumes of chemicals were used in each experiment and so that concentrations were as accurate as possible, as if the concentrations were inaccurate, this could affect my results.
The room temperature was measured and remained constant throughout each experiment and the test was repeated twice to ensure any anomalies could be identified. As I had many results I could calculate an average set of results.
TABLE 1
I can now use these results to calculate a set of average results.
TABLE 2 - AVERAGES
Analysing:
The results clearly show that as the concentration of the hydrochloric acid increases, the time taken for the solution to become opaque decreases. This shows that concentration affects the rate of reaction and that the higher the concentration the greater the rate of reaction.
This pattern can be seen clearly on the graphs, which show a downward curve from left to right.
In conclusion, the concentration of solutions affects the rate of reaction. As the concentration of the hydrochloric acid is increased so is the rate of the reaction and as it is decreased so is the rate of reaction. This is because the more particles there are in a solution, the more chance there is of a collision, and therefore the reaction is sped up. The concentration of the hydrochloric acid affects the reaction speed, as there are more particles on the solution, there is a greater chance that they will collide with sufficient force to react.
The conclusion supports my prediction, as I predicted that as the concentration of the acid increased, the reaction would occur more quickly. This is due to the collision theory, which states that as concentration increases, so does the amount of particles in the solution, which means there is a greater chance of a collision with a force that is sufficient to result in a reaction, therefore increasing the rate of reaction.
Evaluating:
My investigation went according to plan and was carried out safely and as accurately as possible with the methods and equipment I planned to use. The experiment provided me with a good set of results that allowed me to identify anomalies.
There was an anomalous result in the 1st repeat for the reaction where 0.6M hydrochloric acid was used. This anomalous result was most likely due to human error and a mistake in measurement. Although this anomaly occurred, as I had collected many results, I could identify it. The room temperature remained constant during each individual experiment; however, it was not the same for all three experiments. The temperature was higher for the two repeats than it was for the first experiment and this may explain why in the two repeats the reactions occurred faster. This is due to the collision theory, which states that the more kinetic energy particles have, the more chance there is that particles will collide with sufficient force to react, and therefore the reaction is sped up. Particles gain kinetic energy as they gain heat.
My method was very suitable for the investigation as it provided me with a good set of results, and allowed me to carry out a safe and fair test. However, the method could have been improved in a number of ways: I could have made a stock of each concentration of hydrochloric acid rather than diluting the acid separately for each experiment. This would have meant for the solutions would have been of exactly the same concentration for each experiment, as although I measured the volumes with extreme care and with a burette, as I made the solutions for each experiment separately, there is a possibility that the solutions in the three experiments were of a slightly different concentration. A stock of 1M sodium thiosulphate could also have been made, but due to the large volumes of it used, this was not possible with the equipment we had. To measure the point at which the solution became opaque more accurately, I could have used the computer program “Logit” to measure light intensity, had the equipment been available to me. I could have then stopped the experiment at exactly the same point of light intensity for each experiment rather than using my eyes to estimate when the solution was opaque.
My evidence is reliable as the most of the results followed the trend shown in my conclusion. Any anomalous results were identified as I carried out the experiment three times. This also enabled me to get a set of average results and it also showed that the results were not one offs.
To provide further evidence I would investigate the how temperature affected the rate of reaction. I could do this by using a similar set up as for my concentration investigation but using the same concentrations and volumes of sodium thiosulphate and hydrochloric acid and heating the acid to different temperatures such as, 25 degrees, 35 degrees, 45 degrees and 55 degrees. I predict that as the temperature of the acid increases, so does the rate of reaction. This is because the collision theory states that the more kinetic energy particles have, the more chance there is of a collision, and therefore the reaction is sped up. Particles must collide with sufficient force to react. Particles gain kinetic energy as they gain heat, and therefore as the heat of the acid is increased, there is a greater chance that the particles will collide. I would need the following equipment:
Stop clock
Paper with black cross drawn on
100cm3 Conical Flask
100cm3 Measuring Cylinder
Thermometer
Sodium Thiosulphate 0.1M
Hydrochloric Acid 1M
Water Bath
I would use a water bath to heat the acid, as using a Bunsen burner would be more dangerous. In order to ensure a fair test is carried out the temperature of the hydrochloric acid must be the only variable that is changed. The concentrations of the chemicals will affect the reaction speed, as there are more particles on the solution, there is a greater chance that they will collide. This means I must change only the temperature of the hydrochloric acid; the concentration of the sodium thiosulphate and acid must remain the same for each experiment. This is because any inconsistency would make the test unfair.
Measurements should be taken accurately with a burette to maintain the same volumes of chemicals for each experiment. I must make sure that the hydrochloric acid is heated to the correct temperature, and it must be added to the sodium thiosulphate as soon as it is removed from the water bath.
Repeat the test twice to collect many results: this will highlight any irregularities.
