Investigation to find out how the rate of reaction between sodium thiosulphate and hydrochloric acid.

Investigation to find out how the rate of reaction between sodium thiosulphate and hydrochloric acid

Aim

Investigation to find out how the rate of reaction between sodium thiosulphate and hydrochloric acid is affected by changing the concentration of hydrochloric acid

Introduction

In this experiment I am going to find out how the rate of reaction between sodium thiosulphate and hydrochloric acid is affected by changing the concentration.

The equation to this is as follows:

Sodium +Hydrochloric Acid Sodium +Sulphur +Sulphur +water

Thiosulphate Acid Chloride Dioxide

Na2 S2 O3 (aq) +2HCL (aq) NaCl (aq)+ S(s) +SO2(g) + H2O(l)

This reaction usually produces a yellow precipitate.

We place the reaction flask on a card with a black cross-drawn on it. When the cross is completely obscured, the reaction will have finished. The time taken for this to happen is the measure of the rate of reaction. We must do this several times, and change the concentration of sodium thiosulphate.

The rate of reaction is a measure of the change, which happens during a reaction in a single unit of time. The things that affect the rate of reaction are as follows:

Surface area of the reactants-does not apply for this experiment
Concentration of the reactants
The temperature at which the reaction is carried out- If not kept the same particles will get more energy for being of a higher temperature and therefore causing more collisions.
Use of a catalyst- this will speed up a reaction so would affect the rate.

The factor that we are using is Concentration of the reactants.

Preliminary

I have decided to do a preliminary test so that I can decide how to do the investigation, and find what range I will use. I will also be able to find if there are any ways of improving the way we conduct the test.

I have decided to use concentrations 100% 90% 80% 70% 60% of hydrochloric acid to investigate in our preliminary test. We will be generating these on a simulated computer program to get the results.

Apparatus

List of apparatus we would have us if doing by hand and not using computer generated results.

Conical flask
Sodium Thiosulphate (different concentrations)
Hydrochloric acid (same concentration each time)
Water (different concentrations)
Stop watch
Paper with black cross on it
Small meniscus
A large meniscus

Results

Conclusion

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I have decided to use concentrations 100% 90% 80% 70% 60% of hydrochloric acid to investigate in our preliminary test. We will be generating these on a simulated computer program to get the results.

Apparatus

List of apparatus we would have us if doing by hand and not using computer generated results.

Conical flask
Sodium Thiosulphate (different concentrations)
Hydrochloric acid (same concentration each time)
Water (different concentrations)
Stop watch
Paper with black cross on it
Small meniscus
A large meniscus

Results

Conclusion

Plan

Prediction

I think that the higher the concentration we use of sodium thiosulphate, the faster the reaction will happen.

The reason I think that this will happen is because, in a reaction particles collide to give the end results of the reaction. So if there is a higher concentration of particles on a solution, then there will be a high number of collisions. If there are a high number of particles colliding, then there is a higher chance of them reacting.

Apparatus

Conical flask
Sodium thiosulphate (different concentrations)
Hydrochloric acid (same concentration each time)
Water (different concentrations)
Stop watch
Paper with black cross on it
Small meniscus
A large meniscus

Method

Firstly, we collected the apparatus that is listed above. Then, we put 10 cm3 of hydrochloric acid in a conical flask (measuring the HCL with a small meniscus), and then put the conical flask on the black cross on the paper. We then added 50 cm3 of sodium thiosulphate to the hydrochloric acid, and at this time we do not need to add any water. Immediately, we started the stopwatch.

We then waited for the black cross to be completely obscured by the mixture. When this happened we stopped the stopwatch. By this time the mixture was completely yellow. Then we recorded what the time was.

We then emptied out the contents of the conical flask, and cleaned it out, and dried it as best we could. Next, we added 45 cm3 of sodium thiosulphate; we kept the HCL acid constantly at 10 cm3. Now, because we have to keep the volume the same for it to be a fair test, we added 5 cm3 of water. (We had to add the sodium thiosulphate and the water at the same time for this to be a fair test also). We then recorded the time for the cross to become completely obscured.

We repeated this many times, adding different amounts of sodium thiosulphate and water each time, and recording the time taken each time.

Diagram

Fair test

To make this experiment a fair test, we need to make sure we do a number of things.

In this experiment we are trying to find the rate of reaction using concentration as a factor, so there is a number of things we need to make sure we do to keep it a fair test.

Firstly, we need to keep a chemical at a constant concentration. So, in this experiment we have chose to keep hydrochloric acid at a constant concentration. We could have, however, used sodium thiosulphate as a constant, but we had chose to use hydrochloric acid.

Next we must make sure that the solution is kept at a constant volume throughout the experiment. If the volume is different, then it could give different results to if it was at a constant volume.

We must also make sure that we add both the water and the sodium thiosulphate at exactly the same time (into the conical flask with the hydrochloric acid in it), or it could effect the results of the experiment.

We must start the stop watch at the exact time as we put the water and the sodium thiosulphate into the conical flask. To do this it is a lot easier if there are two people doing the experiment, so one person can put the two substances in the HCL, and one person can start the stop watch.

Another thing we must do is to make sure that the conical flask is completely clean and free of any water or any other substance before we attempt to start the next experiment.

Safety

There are a lot of safety issues we must abide by in this experiment also.

We must remember that the substances that we use in this experiment can be very harmful if used the wrong way.

When we do this experiment, it may be necessary to wear safety goggles, as things are very unpredictable, and even though it is very unlikely that the solution would come out of the conical flask during the experiment, one must still be cautious of spills.

We must make sure that coats and bags are all out of the way while doing the experiment. Ties and hair should be tucked out of the way, so they do not make contact with any of the chemicals. It would also be preferable to wear a scientific apron, however this is not essential.

We should also try our best not to spill any chemicals, and we must not eat or drink in the lab while dealing with these harmful chemicals, as they can get on to our hands.

Results

Table of results

1st try:-

2nd try:-

3rd try:-

I have also come up with a set of average results for all 3 experiments:-

Conclusion

Evaluation

I think that most of the experiment I have done has been fine, with as little anomalous results as possible. However, there are still a few anomalous results which I will now point out.

This is the only anomalous result that I have recorded. The result may have turned out anomalous because of basic human error, or maybe because we measured the substances wrong. It may have even been because we did not clean the apparatus properly.

Apart from this, the accuracy of my experiment has been more or less accurate. Although there are a number of ways in which we could have made the results more reliable. For instance, we could have used better measuring equipment, because the apparatus we used was mainly basic equipment.

Another thing we could have done to bring more evidence is to have tried to use the hydrochloric acid as the variable substance, and used the sodium thiosulphate as the constant substance. This would have brought more evidence to support the idea that the higher concentration of a substance, the faster it will react.

I think that the evidence, which I have received, is enough to reach a suitable conclusion, but there are a few flaws to the experiment (which I have mentioned). Apart from them, the experiment is fine.