To get a whole set of results the experiment had to be repeated with all the different concentrations and after that, to get a second run we repeated the wohle procdure.
Apparatus:
- Measuring Cylinders -used to measure the volumes of the solutions
- Stopwatch -used to record the times
- Conical Flask -used to hold the solutions
- Permanent black marker -used to label the flask and to draw a cross
- Thin glass stick -used to mix the different solutions together
- Sodium Thiosulphate
- Hydrochloric Acid
Safty:
There are a few things that you should do in ways of saftyness during the experiment. One very important factor is to wear googles. Googles protect your eyes and one should never forget them.
The other important thing is that one should als be very careful when looking into the conical flaks to check whether the cross has disappeared or not, since the vapor (SO² gas) that you could inhale is toxic.
Fair Test:
It`s very important to have a fair test. In order to do that we have to be careful, trying to keep the same standarts all the time.
- All volumes have to be measured as exact as possibel using a measuring cylinder to avoid incorrectness.
- Use the same stopwatch and the same cross ("X") all the time. Try to avoid the cross getting wet.
- Do all the experiments under the same temperature, which in our case was room temperature.
- The conical flask has to be cleaned each time to ensure that it was not stained with sulphur. The measuring cylinders should be washed out in between each measurement.
- Before the experiment choose one person to judge when the black cross has disappeared so as to reduce human error in the readings.
All those points above should be considered in order to have a succesful experiment and reliable results. It will also keep anomalies ones at a minimum stage.
Research: (Scientific Background)
The reaction rates are explained by the Collision Theory.
The rate of reaction depends on how often and how hard the reacting particles collide with each other.
There are 4 factors that affect the rate of reaction:
1) Temperature
The temperature increases the number of collisions. When the temperature is increased, the particles move quicker, which increases the number of collisions.
2) Concentration
The concentration increases the number of collisions. If the solution is more concentrated, there are more particles of reactants knocking about between the water molecules which makes collisions between the important particles more likely.
3) Surface Area
The larger the surface area, the more collisions. If one reactant is solid then breaking it up into smaller pieces will increase its surface area. The particles around the solution will have more area to work on so there will be more collisions.
4) Catalyst
A catalyst increases the number of collisions. It works by giving the reacting particles a surface to stick to where they can bump into each other. This increases the number of collisions.
Prediction:
I predict that as the concentration of the sodium thiosulphate increases the rate of reaction will also increase.
This can be referred to the collision theory
Results:
These were the results I used to write my conclusion and my evaluation
1st experiment
2nd experiment
The set of results you can see above were taken during all of the experiments. All of the experiments were repeated 2 times in order to receive correct and accurate results. The next step would be to do some calculations with these results.
- During all of the experiments it was made sure that the volume of the total solution was always 55 cm³
- In all of the experiments the volume of the hydrochloric acid was always 5 cm³
These are the calculations i added to my table of results:
Concentration = original concentration x volume of Na2S2O3 /total volume of diluted Na2S2O3
i.e., For 30 cm3 of Na2S2O3 used = 1 x (30/50) = 0.6 M
Rate = Mass of solid sulphur formed/time taken
= 1/time
i.e., for 30 cm3 of Na2S2O3 used = 1/time = 1/10.09 = 0.99
Table of results, including the results of all of the calculations:
2nd experiment
Table including average results:
The reaction between sodium thiosulphate and hydrochloric acid:
Sodium + Hydrochloric sodium + water + sulphur + sulphur
thiosulphate acid chloride dioxide
Na2S2O3 + HCL NaCl + H20 + SO2 + S
Analysis:
Looking at the results, i found out that if the concentration of the sodium thiophate increases the rate of reaction also inreases or the time taken dereases. This indicates that my prediction, which is based on the collision theory, is correct.
The COLLITION THEORY. Increasing and decreasing the rate of reaction can be explained in terms of increasing and decreasing the number of collisions between the two reacting particles.
If the solution is made more concentrated it means there are more particles of reactant knocking about between the water molecules between the important particles more likely.
The two diagrams above show you two different situations of reactions.
In the first diagram, there is a low concentration of red particles (which in this case could be sodium thiosulphate) in a solution, where there are also other particles present (which could be hydrochloric acid). As there is only a low concentration of the one particle, there is only a small chance that the particles will collide and react, which means that the rate of reaction is slow.
In the second diagram, the concentration of red particles, which means that the chance of red and yellow knocking together and reacting is greatly increased.
That is exactly what happened in my experiments in my investigation. As the concentration of sodium thiosulphate was increased, the number of sodium thiosulphate particles in the solution increased, which means that the rate of reaction was also increased.
If you look at the table above, you are able to see that the amount of hydrochloric acid put into the solution was always kept the same. That means that the number of particles of that substance was not changed, which has the advantage that it shows that the hydrochloric acid cannot influence the rate of reaction.
Graphs:
In this course work there should be two graphs, which support my conclusion. First of all I have to say that all of the results were good enough to be as points for the graphs, which not only shows that all of the results were accurate, but it also shows that these results are good enough to be used in my conclusion and analyze part.
Looking at graph no. 1, you are able to see the relationship between the volumes of sodium thiosulphate over the time in seconds. In the first part of the graph you can see that when the concentration of sodium thiosulphate in the solution was very high, it only took a very few seconds until the solution has reached the determined point of cloudiness – the rate of reaction is very fast.
As you go down the graph, this rate of reaction decreases just as the concentration of sodium thiosulphate in the solution decreases. It takes longer and longer until the reaction has come to that level, where the solution has reached the determained point of cloudiness.
Looking at graph no. 2, you are able to see how the concentration of sodium thiosulphate affects the rate of reaction.
In the beginning of the graph, the concentration of the sodium thiosulphate in the solution is low, which also means that the rate of reaction is also low/slow.
As you go along the graph the concentration of sodium thiosulphate in the solution increases and the rate of reaction also increases accordingly.
This graph is very helpful for me as it proofs my analysis section. When the concentration of sodium thiosulphate in the solution is little, there aren’t a lot of required particles available to react, which means that the rate of reaction also remains small.
The results clearly support the idea that, the higher the concentration is the more collisions occur, the faster the rate of reaction.
Evaluation:
Looking at the results and the graph I believe that I did a good job during the experiments, as they are all quite accurate. I didn`t have any anomilus results which proves that the message i have used worked in a sence of successfullness and rilableness. Altough the resulats are ok I still have to say that the procedure could have been more accurate. Especially when you take a look at the measuring devices and the method you`ll realise that they could have been more presice in order to obtain better results. It´s also not very easy to decide when exactly to stop the watch, as it is never really clear when the moment was, when the black cross-disappeared behind the cloudy solution.
If i had the chance to do this experiment again i would change, include or put more attiontion on the following points:
- Try to use better, more accurate equipment that includes:
- Glass pipettes instead of plasic ones which were used to measure out the liquit.
- A different device to determine when the solution has reached a certain level of cloudiness. I am sure that there are specific devices, which do exactly that.
- A little apparatus, which pours the substances into the conical flask, and in the same time start the stopwatch.
- More accurate measuring cylinders one can make sure that the volumes of the substance are accurate.
- I would try and use different chemicals in order to see if it effects the rate of reaction.
- I would do exactly the same experiments but change the amount of solution taken from each substance.
- I would repeat the experiment one more time so that i have alltogehter 3 sets which will lead to more accurate results and averages.