Reaction between hydrochloric acid and sodium thiosulphate.
Sophie Corcoran 11D 6th January 2004
Reaction between hydrochloric acid and sodium thiosulphate
Introduction
I am investigating how different concentrations of thiosulphate and distilled water in ratio to 10cm³ of hydrochloric acid affect the rate of reaction. I will also investigate if there will be a change in temperature after the reaction has occurred. I will know when the reaction is taking place as the solution turns from clear to opaque. The reaction that takes place is as follows: -
Sodium + Hydrochloric --> Sulphur + Sulphur + Sodium + Water
Thiosulphate acid dioxide chloride
Na S O + 2HCl --> S + SO + 2NaCl + H O
The reaction will have finished when the solution has turned completely opaque and it is visible that the solution is not turning increasingly more so. At atomic level, at this point all of the particles in the solution will have stopped colliding.
My prediction
I predict that as the concentration of distilled water to sodium thiosulphate increases, the rate of reaction will take longer as the distilled water is making the solution weaker. This is due to the fact that there will be less fruitful collisions between sodium thiosulphate and the hydrochloric acid. This can be easier described by using the following diagrams: -
Sophie Corcoran 11D 6th January 2004
Here there are many successful collisions between the sodium thiosulphate and the hydrochloric acid because there is a large volume of sodium thiosulphate in ration the volume of water, meaning that the water cannot dilute the solution to a great enough extent.
Here there is no where near as many successful collisions as seen previously. This is because there is a larger volume of water in ration to the volume of sodium thiosulphate, meaning that there will not be as many sodium thiosulphate molecules that would be able to collide successfully.
Due to this collision theory, the higher the concentration of sodium thiosulphate, the quicker the rate of reaction because there will be more successful collisions happening in a shorter space of time. In terms of the temperature change I predict that the more sodium thiosulphate in ratio to ...
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Here there is no where near as many successful collisions as seen previously. This is because there is a larger volume of water in ration to the volume of sodium thiosulphate, meaning that there will not be as many sodium thiosulphate molecules that would be able to collide successfully.
Due to this collision theory, the higher the concentration of sodium thiosulphate, the quicker the rate of reaction because there will be more successful collisions happening in a shorter space of time. In terms of the temperature change I predict that the more sodium thiosulphate in ratio to distilled water, the greater it will be. However, I will say that this change will not be very great, and I may not even be able to measure it in the school laboratory.
Sophie Corcoran 11D 6th January 2004
Method:
Equipment
In this experiment I will be using: -
* Stopwatch
* Measuring cylinder
* Paper marked with an 'X'
* Sodium thiosulphate solution
* Clamp stands
* 2 burettes
* Thermometer
* Distilled water
* Hydrochloric acid
* Small beaker
* 3 large beakers
Plan
Firstly I will set my apparatus up as follows: -
Sophie Corcoran 11D 6th January 2004
I will use the clamp stands to keep the burettes in place, while I am measuring out the volumes of sodium thiosulphate and distilled water. I collected the sodium thiosulphate and water in 2 larger beakers. I then used a measuring cylinder to measure out the hydrochloric acid to 10cm³ exactly, and collected it in a large beaker. I used a thermometer before and after the reaction to help me see if there was change in the temperature. I used a small beaker to mix the solutions of sodium thiosulphate, hydrochloric acid, and water in. I placed the small beaker on the piece of paper marked with the 'X' immediately after this. The 'X' would allow me to calculate when the reaction had completed (when the 'X' would no longer be visible through the solution).
To ensure my experiment is a fair test I will make sure I use 10cm³ of hydrochloric acid each time and that I measure every solution accurately and carefully. Also I will need to make sure I start and stop my timing at the precise moment. Finally I will use the same apparatus throughout the whole experiment, thoroughly cleaning them when needed. This will result in my observations being reliable. Also all the equipment I have chosen to use can be used over and over again, meaning that anybody could do this experiment at any given time using the named apparatus, and they would be ensured to obtain reliable results. I will do this experiment a total of 3 times to ensure the results taken are not anomalous.
From these 3 results I will then create an average of these results. The easiest way to describe how I will get my range of results can be viewed in the following table: -
Volume of sodium thiosulphate / cm³
Volume of water / cm³
Volume of hydrochloric acid / cm³
Time taken / seconds
40
0
0
35
5
0
30
0
0
25
5
0
20
20
0
5
25
0
This would mean that the total volume for the solution would be 50cm³ at all times.
Results
Sophie Corcoran 11D 6th January 2004
Having followed my method, here are the results which the experiment produced: -
Volume of sodium thiosulphate / cm³
Volume of water / cm³
Volume of hydrochloric acid / cm³
Time taken / seconds
Temperature before reaction / °C
Temperature after reaction / °C
Experiment
1 2 3
40
0
0
21
22
23
22
22
35
5
0
29
33
33
22
22
30
0
0
34
32
37
21
21
25
5
0
42
44
45
21
21
20
20
0
66
66
64
21
21
5
25
0
02
04
08
21
21
From these results I was able to calculate the average time taken in each case: -
Volume of sodium thiosulphate / cm³
Volume of water / cm³
Volume of hydrochloric acid / cm³
Time taken / seconds
Temperature before reaction / °C
Temperature after reaction / °C
Average
40
0
0
22
22
22
35
5
0
32
22
22
30
0
0
34
21
21
25
5
0
44
21
21
20
20
0
65
21
21
5
25
0
05
21
21
These results can also be represented in the following graph: -
Sophie Corcoran 11D 6th January 2004
Analysis
On my graph a curve is shown, this allows me to see that my results are correct, as the volume of sodium thiosulphate goes down and more water is added the time taken for a reaction to occur increases. Which is what I predicted would happen, as fewer molecules will collide in a given time. However, as the concentration of sodium thiosulphate decreases the steepness of the curve also decreases to an extent where the line is going in an almost horizontal direction. This would show that the concentration of sodium thiosulphate below this point may not result in the reaction occurring unsuccessfully, or it may take an extremely long time. This point can be seen on my graph at the 15cm³ of sodium thiosulphate intersection with the curve.
My results descend in a rounded curve, however at the point of 35cm³ of sodium thiosulphate and 31 seconds, I obtained an odd result. It doesn't fit into the curve at all. I think this could of happened because of a number of reasons. I could of measured my solutions inaccurately, or stopped or started the stopwatch at the wrong times.
Evaluation
My results are fairly reliable; I know this because the equipment used ensured that reliable results could be obtained. The results are mostly (bar one) all accurate. I can tell this by viewing the curve on my graph as it is regular and has a visible progression. I believe that my results reflect the experiment to a sufficient standard. However, to obtain a more consistent and precise curve, more results could have been taken.
To further my experiment, I could add an extra variable into the experiment, for example, time the rate of reactions of the solutions at different temperatures, and then compare the subsequent results and graphs. This would give me an understanding of how temperature affects rate of reactions.
If I were to do this experiment again, I could make sure that I do not get any anomalies by finding means of measuring the solutions to a more accurate standard, the same could be said for the use of the stopwatch.
