Investigate the concentration of Sodium Thiosulpate and see how it affects the rate of reaction of Hydrochloric acid.

GCSE Science

HCL AND SODIUM THIOSULPHATE

In my investigation I am going to investigate the rate of reaction. The rate of reaction depends on four factors

Temperature

Concentration

Catalyst

Size of particles (surface area)

I have chosen to investigate the concentration of Sodium Thiosulpate and see how it affects the rate of reaction of Hydrochloric acid. I am going to adjust the concentration by adding more or less water and more or less Sodium Thiosulpate but keeping the total amount the same.

Fair test

My experiment will be done as fair as possible. I am making my experiment as fair as possible to make my results more accurate to do this I will have to do these things:

I am going to use the same volume of HCL each time. I will try to keep the same temperature as this could change the speed rate of reaction. The same temperature of water and HCL as this could interfere with the results. The time that the HCL will be measured will be measured to the nearest second as this will give me more accuracy and a fair result. I will repeat the experiment again so I will have three pairs of results and get an average set of results. This will set me to have accurate results.

I cannot control the temperature of the room in so my results could change as the higher the temperature the rate of reaction could change which could change my results. I will try and prevent this by keeping it in a box were the temperature stays the same.

INTRODUCTION

As I mentioned before, the rates of reaction depends on four things. All four methods of increasing the rate of reaction can be explained in terms of the number of collisions.

Temperature increases the number of collisions. When the temperature is increased, the particles all move quicker, they’re going to have more collisions.

Reactions only happen if the particles collide with enough energy. At a higher temperature there will be more particles colliding with enough temperature to make the reaction happen. This initial energy is known as the activation energy, as it is needed to break the initial bonds.

The affect of temperature on rates of reaction is important. Raising the temperature makes the rate of reaction faster. Because the temperature increases, the pressure of the molecules causing them to move faster which will then lead them bump into each other more frequently.

Concentration increases the number of collisions. If the solution is made more concentrated it means it means there are more reactant particles knocking about between the water molecules, which makes collisions between the particles more likely which therefore speeds up the reaction. In a gas, increasing the pressure means the molecules are more squashed up together ...

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If one of the reactants is a solid then breaking it up into smaller pieces will increase its surface are. This means the particles around in the solution will have more area to work so there will be more effective collisions.

A catalyst works by giving the reacting particles a surface to stick to where they can bump into each other. This obviously increases the number of collisions too. Catalyst lower the activation energy of reacting, making it easier for them to happen. This means a lower temperature can be used.

The largest surface area the faster the reaction will bee. This is because there will be a larger area for the particles to collide with. So more collisions will occur and the particles will have more chances to react.

I will be given a solution of Sodium Thiosulphate, this is the most concentrated solution, and I will use the solution and time it accurately. I will dilute it 13 times and repeat the experiment, I then realised the cross would still be visible so 13 times is obviously to dilute. I will therefore dilute it around 5 times and should have measurable readings.

Prediction

What I predict to happen in my experiment is that when I add 50cm3 of Sodium Thioluphate into the flask with the Hydrochloric acid, I hypothesise that the cross is a lot faster than when I add 10cm3 of Hydrochloric acid and 40cm3 of water. This is because I already know that the more Sodium Thiosulphate used the quicker the cross will disappear as I already done research to know this.

Apparatus

Flask Measuring cylinders (50cm3 and

5cm3)

Beaker 1 Beaker 2

Stopwatch Goggles

Water paper with marked cross on it

Safety

I will need to take safety precautions such as using goggles at all times whilst doing the experiment just in case some Thiosulphate goes into my eyes. I will have to wash my hands thoroughly after finishing the experiment to remove the chemicals I have used. I will also have to do my experiment in a spacious place and a big classroom will be ideal.

I will be measuring the amount of Thiosulpahte and water in cm3. There are four different concentrations that I will be experimenting with. These are in a ratio of water: Thiosulphate I will pour the solutions into a flask with a piece of paper with a cross underneath it. I will then time how long how long it takes for the cross to completely disappear. Then I will record the time then repeat the process for he other concentrations.

Accuracy

I feel I have measured with enough accuracy to provide accurate and reliable data:

The concentration of solution I measured to the nearest percentage
The volume of solution was measured to the nearest millilitre.
The time was measured to the nearest second

I am happy with the experiment and feel, my results an I feel they were accurate when repeated. I am also happy with the way I recorded the results.

Water: Thiosulphate

0:50 here I expect the cross to disappear really quickly as there is a high concentration of Thiosulphate and using my background knowledge I know that the more solution of Thiosuphate the quicker the dot will disappear.
10:40 I again expect the cross to disappear quickly but not as quickly as 0:50 as there is less concentration of Thiosulphate and there is a bit water which will slow down the reaction.
20:30 I expect the experiment to be reasonably quick but not as quick as the other two as there is a less concentration of Thiosulphate and more water which obviously will slow down the reaction.
30:20 I expect the experiment to take time as there is more concentration of water than Thiosulphate
40:10 I expect the experiment to take a long time, as there is little Thiosulphate and a lot of water, which will therefore take along time.

Results

Accuracy

I feel I have measured with enough accuracy to provide accurate and reliable data:

The concentration of solution I measured to the nearest percentage
The volume of solution was measured to the nearest millilitre.
The time was measured to the nearest second

I am happy with the experiment and feel, my results an I feel they were accurate when repeated. I am also happy with the way I recorded the results.

The pattern I noticed is the more the concentrated Thiosulphate the quicker the cross will disappear just like I predicted and said.

Analysis

By looking at my graph I can see that when the concentration of the thiosulphate is increased, the time taken for the cross to disappear decreases. This means that the concentration is inversely proportional to the time taken for the cross to disappear.

My results co-ordinate very well with my predictions. I predicted that when I add less Sodium Thiosulphate and more water to the flask the cross will disappear a lot slower, and by looking at my results on the graph I believe that my results do agree with my prediction. I predicted that my results would be accurate and the result compares exactly how I expected the results to be as I said the more Thiosulphate used the quicker the cross will disappear and that is exactly what the graph suggests.

The fact that there are more HCL molecules knocking about the water molecules means that collisions between Thiosulphate are more likely to occur.

To sum all this information up basically the particles have to collide in order to react, and they have to collide hard enough as well. My results

Evidence

I believe that I have an accurate set of results and that I have enough results to be sure about my conclusion. My results are accurate as when I read the collision theory it told my exactly what my results told me. I do not have any outlying results which do not fit I the pattern because my predictions co-ordinated with my results very well.

My method of carrying my experiment was fairly accurate as I made sure that I washed the flask clean for the other concentrations and repeated the experiments. I measured the same amount of solutions in each time and I stopped the stopwatch as soon as I though the cross had disappeared. I think that I should have used four different concentrations because this would be fairer and there would not be any water at the bottom of the flask.

If I was to do the experiment again I could improve the accuracy and reliability of my results by having a range of different concentrations, also I could use the same amount of flasks for the number of different concentrations I use.

If I had more time I could do extra experiments to investigate another factor such as the affects of temperature on a rate of reaction. Also and I could investigate the affects of pressure on a rate of reaction.