My aim is to investigate one effect of concentration on the rate of reaction between sodium thiosulphate solutions and dilute hydrochloric acid.

Tom Bill Science Coursework

Investigation

The Apparatus I intend to use is as follows:

Beakers (250ml & 100ml)
Stop clock
Measuring cylinder
Paper with cross
Hydrochloric acid
Sodium Thiosulphate
Safety goggles
Conical Flask (100ml & 250ml)

I predict that a higher concentration of sodium thiosulphate will increase the reaction rate and a low concentration will lower the reaction rate and increase the time taken for the reaction.

HIGH CONCENTRATION = FAST REACTION = HIGH RATE = DECREASED TIME

LOW CONCENTRATION = SLOW REACTION = LOW RATE = INCREASED TIME

Explanation of prediction

Increasing the number of particles in the same volume increases the chance that the particles will collide. This means that there will be more collisions in a given amount of time.

Here is an example form a metal chip reaction experiment which was also on of my preliminary experiments:

Method

Firstly I will draw a cross on a piece of paper, and then I will put sodium thiosulphate into a beaker (50ml, 40ml, 30ml, 20ml, and 10ml) and water (0ml, 10ml, 20ml, 30ml, and 40ml) I will test each of the 5 concentrations 3 times). To each of the concentrations I will add 5ml of hydrochloric acid and then mix. I will time the reaction until the cross is no longer visible under the beaker looking through the solution it self. After each test I will rinse the equipment and dry before I repeat the experiment to ...

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Method

I will use 10ml cylinder to measure the Hydrochloric acid and a 50ml cylinder to measure the sodium thiosulphate solution. I will keep the experiment at a constant temperature because a rise in temperature could speed up the reaction or a decrease in temperature could slow down the reaction either of these would mean the experiment was unfair. The overall of volume of the solution will remain constant. As will the volume of hydrochloric acid. If these volumes were change then my results would not be correct and it would be a fair test. I will record my results in this table:

Analysis

After I had taken the results (each concentration 3 times) I added the three results from the same concentrations together and divided them three, this gives my the mean time for each concentration . With this mean time I could now go on to work out the rate.

From my table of results I have noticed certain trends:

The higher the concentration the faster the reaction and the faster the time this gives you a high rate. Of course this means that if you lower the concentration the reaction is slower there for the rate is lower. These trends are true my prediction.

I have plotted two graphs from my results. A graph to show the time vs. the volume of thiosulphate and a graph to show the Rate of reaction vs. the concentration. All graphs have a line of best fit.

Looking at my graphs I can see that in the rate vs. concentration graph that the rate rises proportionally to the concentration. This is because when the concentration is increased there are more particles to collide, making the reaction quicker. This produces a virtually straight line of best fit.

I can also see that in the time vs. volume graph that time also reflects the volume proportionally, although the time does increase dramatically as the volume of thiosulphate decreases this because there are fewer particles to collide making the reaction slower. This produces a curved line of best fit. I drew the line of best fit on both graphs with an equal amount of points below, above and trough the line.

In conclusion:

I have found out that when the concentration is higher the time decreases, the reaction is faster and the rate is higher and also that when the concentration is lower the time increases, the reaction is slower and the rate decreases.

I explained the theory to this after my prediction on page one.

I was easily able to analyze my results, and I could see that I achieved correct results according to my prediction and that my prediction was correct.

Evaluation

What could have gone wrong?

I could have measured the volumes incorrectly, either by human error or by using the incorrect gauge on my measuring equipment.

There could have also been human errors with the timing.

Could I have been More Accurate?

I could have been more accurate by using a burette instead of a measuring cylinder to measure the volumes. Unfortunately this equipment was not available to me at the time of the experiment.

I did how ever make the experiment as accurate as I could by using the equipment at hand. I did this by using the correct gauge of measurements for the specific volumes. E.G. a smaller gauge for the smaller measurements and a larger gauge for the bigger measurements this meant that the measurements were more accurate.