The effect of concentration of sodium thiosulphate on the reaction between hydrochloric acid and sodium thiosulphate.

The effect of concentration of sodium thiosulphate on the reaction between hydrochloric acid and sodium thiosulphate

Aim:

With the knowledge from our preliminary experiment, I will be trying to find out the rate of reaction between the two chemicals. We are investigating whether the effect of concentration of sodium thiosulphate will change the rate of reaction. I want to make it a fair test so it will be better for the accuracy of my future results, I think if I do a fair test it will be reflected in my results. A fair test will be done to make sure that I do not mix any of the chemicals together and accurately measure amounts of chemicals used. I will also try to keep out as many factors, which are avoidable, but inevitably there will be things, which I cannot avoid, I will try to keep the test constant, as it will make it even more fairer.

Apparatus:

Flask, measuring cylinder, paper labelled with an, ‘X’, stirring rod, stop-clock, safety mat, and safety goggles.

Method:

Using the equipment in the previous diagram, I will do the experiment in the following manner:

·I will put 50cm³ of 40g/dm³ sodium thiosulphate solution into a flask.

·I will measure out 5cm³ of dilute hydrochloric acid and place it in a measuring cylinder.

·I will add the acid to the flask and start the clock.

·I will stir the flask to mix the solutions with a stirrer.

·I will place the flask on to the piece of paper labelled with the ‘X’ on it.

·I will look down at the ‘X’ from above it, when the ‘X’ disappears, stop the clock and note down the time, of how long it took for the ‘X’ to disappear completely.

This process needs to ...

This is a preview of the whole essay

·I will measure out 5cm³ of dilute hydrochloric acid and place it in a measuring cylinder.

·I will add the acid to the flask and start the clock.

·I will stir the flask to mix the solutions with a stirrer.

·I will place the flask on to the piece of paper labelled with the ‘X’ on it.

·I will look down at the ‘X’ from above it, when the ‘X’ disappears, stop the clock and note down the time, of how long it took for the ‘X’ to disappear completely.

This process needs to be repeated about three or four times if time is available. This will be a way of making the experiment fair. This is because if we repeat the experiment it gives us more accurate results, this is because we can calculate the average of each results and plot them on a graph, which will show the accuracy of the results. Also we need to change the concentration value in order to gain other results. The way I will get various other results will be by adding water to effect the concentration of the sodium thiosulphate solution. I will repeat this with different volumes of water being added to the solution. For my results, I will calculate the concentration of sodium thiosulphate in the flask at the start of each experiment. I will also calculate the reaction rate, by using the formula of 1/time. After that I will plot a graph to show how the rate of reaction varies with the concentration of the sodium thiosulphate solution. The graph will have the reaction rate on the y-axis and the concentration on the x-axis.

Conclusion

The graphs show that the higher the concentration of sodium thiosulphate solution, the quicker the reaction rate was. In my experiment, I proved this in my results. When I started with a very high concentration of sodium thiosulphate solution, the reaction rate was very quick but when the concentration went down so did the speed of the reaction rate.

The effect of the amount of water added to the solution proved to be of great significance. As I kept adding water to the solution it brought down the reaction rate quite hugely. The adding of the water makes the solution a lot more diluted, which means it is a lot less concentrated. My results seemed to be what I predicted, so I am pleased with the outcome. What I predicted which was if I doubled the concentration, I would double the reaction rate. From my results, it has roughly been true, for example the reaction rate at when the volume of sodium thiosulphate was at 25cm³, the rate was 0.0161 1/s, when I doubled the volume the rate was 0.0303 1/s, which is approximately double. I have therefore proved that my prediction was correct.

As I doubled the concentration, the reaction rate grew, this is because of the particles, which are available to hit and collide with each other. It increases the chances of successful collisions, i.e. the ones that involve bonds being broken down in the reactants – sodium thiosulphate and hydrochloric acid. After these bonds have been broken down the reaction can happen. This is what my results have shown.

Evaluation

There were many things, which could have hindered the fairness of my experiment, leading to poor results such as:

Contamination of chemicals in flasks.
Poor measurements of chemical usage.
Starting and the stopping of the stop clocks at the exact right time.

If I contaminated the chemicals in the flasks and did not clean them properly, this could have lead to quicker or slower reaction rates. If I did this it would not have been a fair test. But sometimes things like this are unavoidable; as we do not have these facilities at school where we can make sure that it is a fair test. So little chemical spillages and mixes are quite hard to avoid. Anomalous results could have happened due to these problems but luckily there wasn’t any in my results, which is clearly shown by the shape of the graph.

Poor measurements of chemicals were one of the problems that I encountered quite frequently. If we used a pipette in the experiment it would have been much easier as overfilling in flasks can happen when you pour it into flasks, as it is hard to control the flow. But if we used a pipette it would have been so much easier as you can put a drop in at a time, this is far more accurate and is quicker.

The starting and the stopping of the clock was crucial as well because if you started it that little bit too late or too early the results would have been inaccurate. But as you have to judge for yourself as to when the reaction is finished or not, it could be wrong due to safety goggles being dirty or if you have bad eyesight, it is your own opinion, so it’s your decision.