In my experiment I will find out what makes a reaction between sodium thiosulphate and hydrochloric faster.

These are they ways the atoms collide.

I will do the experiment at least five times to give me a range of results, which will help me to spot any anomalies. I will go down to 1cm³ of hydrochloric acid and up to 24cm³ of distilled water. I will use 1cm³, 2cm³, 3cm³, 5cm³, 10cm³, 15cm³, 20cm³ and 25cm³. It is a fair test as I will the temperature the same; I will keep the molar of the liquids the same; I will use the liquid from the same container each time as not all the liquids will be the same and I will keep the measurement of the sodium thiosulphate the same. I will also use safety glasses as if the liquids go in my eye they could be dangerous. I will keep the temperature the same as this might effect the results as if it a higher temperature than all the rest, it will have added energy which would not make it a fair test.

Prediction

I think that the less water is in the concentration, the quicker it will react.

Justification

The ions are closer together in a concentrated solution. The closer together they are, the more often the ions collide. The more often they collide, the more chance they have of reacting. So if the solution is less concentrated the less chance there is of them colliding so the time in which they react will go down. 

Diagram

Here is a diagram of what my experiment looked like:

This is what the object that we saw through the flask looked like:

Preliminary experiment

I did a preliminary experiment because I needed to find out which was the lowest amount of hydrochloric acid I could use. I found out that it works out that I could go down to 1cm³ of hydrochloric acid before it took to long to do.

Apparatus

• A conical flask
• Hydrochloric acid
• Sodium thoisulphate
• Distilled water
• Stop watch
• Paper design to go underneath flask
• Cylinder

Method

1. First I put 25cm³ of sodium thiosulphate into a conical flask.

2. I then measured out 5cm³ of hydrochloric acid (for the preliminary experiment put used 25cm³ on the real experiment) and 20cm³ of distilled water and put them together.

3. I then poured the mixture of distilled water and sodium thoisulphate into the conical flask with the hydrochloric acid in.

4. I then timed how long it took for the liquids to react so that I could not see the picture underneath.

Results

Actual Results for experiment 1

Experiment 2

Experiment 3

I have highlighted the anomalies in red to make them stand out from the right ones.

Analysing

My results show me that as the concentration of hydrochloric acid goes down, the time it takes to react goes up. This shows that it is a negative correlation.

My research shows that the higher the concentration the more chance there is of ions colliding. This theory agrees which what my results show. These results and research also agree with my prediction. Therefore my prediction was correct.

The reason that I got a straight line for the 1/time graph is that the faster the faster the reaction, the less time it takes to react. This can also be said as the speed of the reaction is inversely proportional to the time it takes to react. This is:

Speed of reaction      1/time

And:

1/time      concentration

So:

Speed of reaction      concentration.

In this experiment the concentration of hydrochloric acid was altered. This means that if we doubled the concentration of the acid then the speeds would double. The reason for this is that the ions will be closer together in double the concentration of the acid. The closer the ions, the more chance they will collide and the more often they collide, the more chance there is of it reacting.

Evaluating

I think that this experiment was not totally fair as it was hard to find out when exactly, the sodium thiosulphate and hydrochloric acid had actually reacted. To make it better I would use a light senor and detect it by that.

I have done one of my experiments by using a light sensor. I did three different concentrations: 50cm³ of sodium thiosulphate and 50cm³ of hydrochloric acid; 50cm³ sodium thiosulphate, 25cm³ of hydrochloric acid and 25cm³ of distilled water; and 50cm³ thiosulphate, 10cm³ of hydrochloric acid and 40cm³ of distilled water. The graph to show it is at the back. I would not do this as the real experiment as it would have taken too long and I would not have had enough results on one graph.

On my graph I found 3 anomalies. The first two, which were both in the 2nd experiment, both had to be redone and are found in the 3rd experiment. The 3rd one in found on the graph with the anomaly.

I think that my prediction was correct as the acid with no water in was most effective in the experiment.

If I was to do an other investigation on the lines of this one, I would probably change the temperature of the acid or sodium thiosulphate.