An investigation into how concentration affects the rate of reaction between Sodium Thiosulphate and Hydrochloric acid
An investigation into how concentration affects the rate of reaction between Sodium Thiosulphate and Hydrochloric acid
In this experiment I am going to find out how the rate of reaction between sodium Thiosulphate and hydrochloric acid is affected by changing the concentration of Hydrochloric acid..
We will be placing the mixture of both liquids on a paper with a black cross-drawn on, once the mixture begins to turn cloudy and the cross is no longer able to be seen, the reaction would have taken place. We will be measuring the time taken for this to happen, and therefore measure the rate of reaction. We will be doing this several times, changing the concentration of Hydrochloric acid, and completing the experiment of each level of concentration three times in order to gain an average result for each.
The input variable we will be changing is the concentration of Hydrochloric acid. We are going to vary this factor to see what concentration of HCL is the fastest to react with Sodium Thiosulphate, and to measure the rate of reaction.
The variable we will be measuring to find out how the effect the concentration has will be the time taken for the reaction to complete.
Plan
Below is a list of apparatus I will need to complete the experiment .
· Sodium Thiosulphate (50 cm3 each time)
· Hydrochloric acid (a total of 100 cm3 but varying in concentration each time)
· Conical flask.
· Distilled water
· Stop watch
· Paper with black cross on it
· Small measuring cylinder
· Large measuring cylinder
I will be using five different concentrations of Hydrochloric acid.
Below is a table to show how to make a particular concentration of hydrochloric acid.
0.2
20
80
0.4
40
60
0.6
60
40
0.8
80
20
Method
Firstly we measured out our first concentration of hydrochloric acid (0.2) using 20 cm3 of Hydrochloric acid and 80cm3 of distilled water. We then poured 50 cm3 of Sodium Thiosulphate into a conical flask and placed it over the piece of paper with a black cross drawn on. We then poured 5 cm3 of the 0.2 ...
This is a preview of the whole essay
Below is a table to show how to make a particular concentration of hydrochloric acid.
0.2
20
80
0.4
40
60
0.6
60
40
0.8
80
20
Method
Firstly we measured out our first concentration of hydrochloric acid (0.2) using 20 cm3 of Hydrochloric acid and 80cm3 of distilled water. We then poured 50 cm3 of Sodium Thiosulphate into a conical flask and placed it over the piece of paper with a black cross drawn on. We then poured 5 cm3 of the 0.2 concentration into the Sodium Thiosulphate and started the stopwatch.
We then waited till the black cross could no longer be seen as the mixture was completely clouded. We stopped the stopwatch and recorded what the time was.
We completed the same procedure for each level of concentration three times, then enabling us to find an average for the amount of time each level of concentration took to react.
In order to keep the experiment fair, I will need to keep four factors constant throughout. Below are the four different factors and the reasons why I have decided I need to keep them the same.
Temperature: temperature is a known factor of affecting the rate of reaction. The temperature of a liquid increasing causes particles to move faster, therefore colliding more, meaning more successful collisions which increases the rate of reaction. Whilst looking at how concentration affects the rate of reaction, I need to keep the temperate the same in order to make sure the concentration is the only factor affecting the rate of reaction.
The hydrochloric acid and Sodium Thiosulphate will both be from bottles left at room temperature, and should therefore be the same temperature. Throughout the experiment, I will also be using a thermometer to ensure the temperatures of the two liquids do not dramatically change.
Volume of both Hydrochloric acid and Sodium Thiosulphate: the more volume of a liquid, the more particles it has to collide and therefore increase the rate of reaction. To prevent this from happening, and making sure the volume of both the liquids does not affect the rate of reaction, I will be using the same amount of Hydrochloric acid, (mixed with the distilled water, depending on what concentration I am making), and Sodium Thiosulphate each time.
Pressure and surface area: these are both known factors that affect the rate of reaction, but as I am using two liquids, and doing each part of the experiment on the same day, these certain factors should not affect the experiment.
Catalyst: a catalyst is a chemical substance that increases the rate of a reaction without being consumed; after the reaction it can be recovered from the reaction mixture chemically unchanged. The catalyst allows the reaction to proceed more quickly or at a lower temperature. To make sure a catalyst does not affect the rate of reaction in this particular experiment, I will simply not be adding a catalyst.
There are also a number of other things to consider to ensure a fair test.
Both the Hydrochloric acid and Sodium Thiosulphate should be poured into the conical flask at exactly the same time, otherwise this could potentially affect the results.
The stop watch should also be started at the same time each time, as the two liquids are poured into the conical flask. To ensure this always happens, one person will be starting the stop watch as the other person pours in the two liquids.
This also applies for judging when the cross can no longer be seen, and to ensure this is also the same each time, the same person will do this throughout.
Safety
Safety is an important factor when completing any experiment, and as we will be using substances that could potentially be very harmful, we will need to follow a few simple safety guidelines.
Firstly we should ensure coats and bags are out of the way and tie back hair to make sure the substances do not come into contact with these. It would also be sensible to wear safety goggles whilst competing the experiment, for the very unlikely yet possible chance the mixture could come out of the conical flask.
Prediction
I think that the higher the concentration we use of Hydrochloric acid, the faster the reaction will happen and the cross will not be able to be seen.
As we increase each level of concentration, I predict the time taken for the cross to no longer be seen will decrease.
The reason I think that this will happen is because the higher concentration of a solution, the more particles there are. If there is a larger number of particles, there is a higher chance of them colliding and more successful collisions taking place. Therefore increasing the rate of reaction.
I also predict if I double the level of concentration, the rate of reaction will be halved. I have drawn a diagram to explain this.
Conclusion of results table
Looking at my results table, I am able to prove my prediction was correct. As we increased the level of concentration of Hydrochloric acid, the rate of reaction was quicker, the time taken for the cross to no longer be seen decreased.
The reason I wrote my prediction was, as the concentration of a solution becomes higher, the number of particles increased which means there is more chance of successful collisions which would increase the rate of reaction. My results table shows this, as I increased the concentration, the time taken decreased.
Using the results from my table, I will now go on to draw a graph using the average time for each level of concentration.
Evaluation
Looking back at the experiment and my results I am able to see my experiment was fairly accurate. There were no anomalous results which shows we were very accurate and careful whilst completing each part of the experiment.
However, there are a number of ways the accuracy of the experiment could have been improved. For example, using more accurate measuring equipment and ensuring to be completely accurate when choosing to stop the stop watch. As this was purely left down to the interpretation of one person, there was room for human error.
Another way to improve accuracy would have been to ensure the temperature was kept the same at all times throughout the experiment, making sure temperature was not a factor affecting the rate of reaction.