Investigating the effect of temperature on the rate of reaction of sodium thiosulphate and acid.

Chemistry Investigation

Sodium Thiosulphate and Hydrochloric Acid

Reaction

Planning

I will investigate the effect of temperature on the rate of reaction of sodium thiosulphate and acid. I will keep the acid and sodium thiosulphate concentration constant and vary the temperature. The maximum volume in total will be 60cm³ cubed.

The rate of reaction will be found by finding the time for a cross drawn on a piece of paper with a pencil and placed under a conical flask to disappear from sight when looked at from above. It disappears because the sulphur formed is a solid and forms a cloud of fine particles through which you cannot see.

Simple Plan:

Add 30ml of water to a measuring cylinder
Add 20ml of Sodium Thiosulphate to the same cylinder
Heat (or cool) the solution to one of the desired temperatures (shown below)
Add 10ml of acid to a separate cylinder
Add the acid to a conical flask placed above a piece of paper with a cross on it
Mix the Sodium Thiosulphate with the acid and begin timing the experiment

For safety I will need to wear protective goggles to shield my eyes from the chemicals. I will need to be careful when measuring the acid too as it is corrosive. I will put a mat on the table whilst I pour the chemicals so as not to damage the table.

I will make my testing fair by making sure that the same person times all of my experiments. This will make sure that all the timing is reasonably accurate as the person timing the experiments will make a similar decision when the reaction has occurred and the black cross can no longer be seen.

To make my testing fair, I could also do multiple tests using the same temperatures and concentration and getting an average for my answers. I could also compare the results with another group’s work.

They key factor in my experiment is the concentration of the sodium thiosulphate solution. This is because the more concentrated the solution, the faster the reaction will take place as there are more collisions during the reaction. My concentration will be 20ml sodium thiosulphate and 30ml water. The temperature of the sodium thiosulphate solution is very important as the hotter the sodium thiosulphate the faster the reaction will occur as the particles in the experiment move around faster and contain more energy. This gives them a greater chance of colliding with other particles with enough energy to make the collisions active.

If the concentration of sodium thiosulphate was any greater, we would struggle to time the experiment as it reacts very quickly. We discovered this during our preliminary work in class.

Activation energy is the minimum amount of energy which particles require to react when they collide. This is because there are bonds which need to be broken to form new chemicals. I will control the temperature of the Sodium Thiosulphate solution in the experiment.

The concentration of acid is important as this could change the rate of reaction. In this experiment, the acid concentration will remain the ...

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If the concentration of sodium thiosulphate was any greater, we would struggle to time the experiment as it reacts very quickly. We discovered this during our preliminary work in class.

The concentration of acid is important as this could change the rate of reaction. In this experiment, the acid concentration will remain the same at 10ml and the intensity of the pencil on the piece of paper. This is because if the intensity is high, the reaction will take too long.

For my investigation I will change the temperature of the sodium thiosulphate solution. This will speed up or slow down the reaction times depending on the temperature. I will use the concentration 20ml / 30ml (20ml being the sodium thiosulphate and 30ml being water). The acid will not be heated.

I will use five different temperatures, 20°c, 30°c, 40°c, 50°c and 60°c to obtain a large enough range of measurements. I will then compare my work with another group to see if our results are similar and reliable.

The factors I will control are the concentrations of sodium thiosulphate. I will control the timing of the reactions, the temperature of the sodium thiosulphate and the concentration of the acid.

When I make my prediction I will take into account that the following factors can affect the experiment:

The concentration of Sodium Thiosulphate
The temperature of the Sodium Thiosulphate

For my prediction, I predict that the higher the temperature (the temperature of the sodium thiosulphate solution is very important as the hotter the sodium thiosulphate the faster the reaction will occur as the particles in the experiment move around faster and contain more energy). This gives them a greater chance of colliding with other particles with enough energy to make the collisions active.

The volume of sodium thiosulphate will also be an important factor as the more sodium thiosulphate there is the more chance there is of a collision between particles. The fewer amount of particles there are, the less chance there is of a reaction taking place. My concentration is only 2/5 sodium thiosulphate because any larger amount would be difficult to time, as the reaction we tested in class before this experiment was far to fast to measure at larger concentrations.

I will use a maximum of 60ml of volume. The ranges of measurements which I will take include the following concentrations of Acid and Sodium Thiosulphate:

To obtain the correct concentration of Sodium Thiosulphate, I will dilute the solution. So for example, I will add 30ml of water to the 20ml of Sodium Thiosulphate.

I think that this range will give a reasonable measurement of results for me to analyse. This will be adequate enough to plot graphs.

My quantitative prediction for this investigation is that for every 10 degrees temperature rise, the rate of reaction will double. This means the hotter my sodium thiosulphate, the faster the reaction will occur.

Obtaining

To perform my experiment, I will need the following equipment:

Sodium Thiosulphate Solution
Hydrochloric Acid
1 Thermometer
1 Beaker
2 Measuring Cylinders
1 Conical Flask
1 Tripod
1 Heatproof Mat
1 Stopwatch
1 Bunsen burner
X on a Piece of Paper
1 Pair of Tongs
1 Pair of Goggles
1 Apron

I will need a pair of safety goggles so I do not get any acid in my eyes. I will also need a pair of tongs so I don’t burn my hands moving the conical flask, which is heated in very hot water, onto the paper with a cross on it.

My measurements of the experiment are shown in the table below:

I believe these results to be accurate as they are all similar and they all go in sequence. They follow the trend that: the higher the temperature, the quicker the reaction. Such as the result at 20°c is 75.70 seconds (average result) and at 60°c the experiment is 13.03 seconds (average result).

I have taken another group’s results to study against my own and they are shown in the table below. The other group used the same temperatures and concentrations as my group, so I predict that there results will be very similar to my own.

I believe these results to be reasonably similar to my own results. I think that this provides good evidence that the experiment was done correctly. This makes my results more reliable.

I think I have a large enough range of results at different temperatures to make accurate observations. I also studied another group’s work consisting of the same temperatures and the same concentration (20ml Sodium Thiosulphate and 30ml Water).

My equipment was used to precision as my temperatures were recorded to within 1 or 2 degrees Celsius when I added the sodium thiosulphate solution and I started timing the experiment.

Analysing

By doing this experiment I have found out that the higher the temperature, the faster the reaction takes place. This is because the particles have more energy and move faster. This gives them more chance of colliding with other particles and reacting. I also found out that at the lowest temperature (which was 20°c); the reaction took 75.70 seconds (average result of my experiments).

The graph shows that the higher the temperature, the faster the rate of the reaction. For example, at 20°c the experiment took 76.81 seconds. But at 60°c the experiment took 13.26 seconds.

The graph agrees with the one above. For example, at 20°c the experiment took 74.59 seconds. But at 60°c the experiment took 12.8 seconds.

The graph above shows that the overall trend of results agrees with my prediction. The higher the temperature, the faster the rate of reaction. There are no measurements which are out of place so I believe I have completed the experiments accurately.

The second group’s results agree with my results - though the times are a little higher. In the experiment of the second group, the time at 20°c is 76.81 seconds longer than my test and the time at 60°c is 13.26 seconds higher than my results.

This graph is similar to the one above. It has the same trend and similar measurements.

There are no results which are out of place, showing that the second groups experiment’s can be considered as reliable evidence.

This graph is for the average results of the second group. It shows that the trend is a reasonably steady downward sloping line. This is reliable as there are no measurements which are miss fitting to the line, though there is a slight dip at the 40°c measurement, it is not big enough to be considered out of place and therefore can be ignored.

Evaluating Evidence

My method was good enough to make a conclusion because I gathered a large enough range of results to make accurate observations from. I also studied another group’s work to see if their results agreed with what I had measured.

I believe that I had enough evidence because I had a large range of results which were similar to each other.

Most of my measurements were accurate and fit in with my prediction and the rules of science (the hotter particles are, the faster they react). The only result which I believe to be out of place is the second groups average results. Though there is a slight dip at the 40°c measurement, it is not big enough to be considered out of place and therefore can be ignored. I believe them to be out of place because they were probably timed in-accurately.

I have gathered enough evidence to support my firm conclusion that the hotter the Sodium Thiosulphate, the quicker the reaction. I wrote this for my prediction and all of the results from my group and the second groups experiments show this.

To further improve my experiment and add additional conclusive data, I would test a larger range of temperatures. For example, test every 5°c instead of testing every 10°c to improve the accuracy of my results. This would extend my investigation. I would also test higher and lower temperatures (starting from 5°c to 95°c instead of 20°c to 60°c). This would give a larger range of data for me to analyse and draw a conclusion from.