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Monday, March 26, 2012

Affects on varous acid concentrations

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An Investigation To Ascertain The Effects Of Various Acid Concentrations On The Rate Of Reactions.


Aim


This experiment is to determine if the concentration of sodium thiosulphate affects the rate of the chemical reactions with hydrochloric acid, resulting in the solution becoming cloudy.


Fair Test


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All liquids used in the experiment are required to be at the same temperature. Substances that are at a higher temperature have absorbed energy. This causes the movement of particles to increase resulting in them colliding with other particles more frequently. This is one of the factors which determines the rate at which the particles react with one another. Consequently, liquids at a lower temperature contains slower moving particles, reducing the rate of reaction. Therefore it is important to maintain the temperatures the same to enable a fair test.


The concentration of the hydrochloric acid must be kept the same. A lower concentration means less particles in the solution, therefore less collisions resulting in a reduced reaction rate. A higher concentration has more particles in the solution with more collisions occurring, causing an increased reaction rate.


In order for the experiment to be accurate, clean equipment is required for each experiment to reduce the risk of cross-contamination.


But the same cross drawn on paper using a black pen must be used for every experiment to keep the darkness of the cross the same.


The volumes of the chemicals used in each experiment must be consistent as different volumes will cause different concentrations of particles; affecting the final result.


A stopwatch must be used to record the time take for the reaction to take place. The stopwatch is pressed to start when the sodium thiosulphate is added to the hydrochloric acid and pressed to stop when the cross under the conical flask becomes opaque.


The time of the reaction and the concentration of the sodium thiosulphate must be recorded immediately.


Variables


The variable in this experiment is the concentration of sodium thiosulphate. Different concentrations of this chemical is used to determine the effect of the rate of reaction.


Prediction


I predict that the higher the concentration of sodium thiosulphate on hydrochloric acid, the quicker the rate of reaction. The lower the concentration of sodium thiosulphate on hydrochloric acid, the slower the rate of reaction.


Apparatus


Marker pen


Measuring cylinders


Conical flask


Sodium thiosulphate


Hydrochloric acid


Goggles


Stopwatch


Paper


Water


Method


Collect apparatus and set up appropriately. Draw a large black cross in the centre of the paper. Place the conical flask on top of it, making sure the black cross is visible. Measure 50ml of sodium thiosulphate in a measuring cylinder and pour into the conical flask. Measure 5ml of hydrochloric acid and add to the sodium thiosulphate. When added, start the stopwatch to find out how long it takes for the liquid to turn cloudy and disappear. Record the time take. Repeat this procedure with clean measuring cylinders and conical flasks. To reduce the concentration of sodium thiosulphate, add 5ml of water to 45ml of sodium thiosulphate. Following experiments need a decreasing concentration of sodium thiosulphate by reducing the volume of sodium thiosulphate by 5ml and increasing the volume of water by 5ml, so the overall volume is 50ml. repeat until there is 5ml of sodium thiosulphate and 5ml of water. Repeat each experiment times and carefully record the results.


Pilot Test


To find the appropriate volume to use for the test in order that the experiment can be carried out in a reasonable time. The following shows the volumes used and the times to establish a suitable volume to use in the main experiment.


Volume of sodium thiosulphate (ml) Volume of water


(ml) Time take to react with 5ml of hydrochloric acid (s)


50 0 5


5 5 58


5 45 541


Decided Range


Volume of sodium thiosulphate Volume of water (ml)


50 0


45 5


40 10


5 15


0 0


5 5


Analysing


The results show that the concentration of sodium thiosulphate effects the time at which the reaction takes place, that is, the rate of reaction. This is represented by the straight line graph which shows that the lower the concentration of sodium thiosulphate, the more time it takes for the solution to become opaque, therefore the slower the rate of reaction. The higher the concentration of sodium thiosulphate, the less time it takes for the solution to become opaque, therefore there is an increase in the rate of reaction.


The increase in the straight line shows the increase in the rate of reaction as it takes a shorter period of time for the increase to occur.


The majority of the experimental results are on the graph line, but even the points that are not have still shown an increase in the rate of reaction. The results correspond with my prediction. An example of two of ht points that do lie on the line of the graph are when the concentration of sodium thiosulphate is at 0.1M and the result of the reaction was 6 seconds, while according to the graph it should have been 4 seconds. Also when the concentration of sodium thiosulphate was 0.15M the result was 0seconds when it should have been 1.5 seconds.


Scientific Reason


The difference of the rate of reaction depends upon the concentration of sodium thiosulphate. The lower the concentration of sodium thiosulphate the less particles are present in the solution when added to the hydrochloric acid, whose concentration of particles remains the same. The higher the concentration of sodium thiosulphate means the presence of more particles therefore the chance of these particles colliding with the hydrochloric acid are increased. This will take less time meaning an increase in the rate of reaction.


Conclusion


When the concentration of sodium thiosulphate increases, the rate of reaction for the solution to turn opaque also increases. The experimental results are accurate because they show an increase in the rate of reaction when there is an increase in the concentration of sodium thiosulphate. Although some points on the graph do not exactly fit lie on the line of best fit they show an accurate result. When the volume of sodium thiosulphate is 50ml and the concentration is 0.16M, the average time taken for the cross to disappear is seconds. But when the volume of sodium thiosulphate is 5ml and the concentration is 0.08M the time taken for the cross to disappear is 70 seconds. This shows that when the concentration of sodium thiosulphate increases, so does the rate of reaction.


Evaluating


The results obtained from the six concentrations of sodium thiosulphate are fairly accurate according to the line of best fit on the graph. Each experiment on the individual concentrations were done times to produce an average time. To calculate the rate of reaction, the results was used in the following formula


1 second/ average time (s) = s x 1000 = rate of reaction


These are the anomalies results. The first set of experiments done with the higher concentration of sodium thiosulphate, seem to have very close results, but the results from the experiments when the concentration of sodium thiosulphate is lower, and the rate of reaction is slower, the results seem to vary quite a lot. An example of when the concentration sodium thiosulphate Is 0.16M the difference in time over results was seconds. When the concentration of sodium thiosulphate was 0.08M, the difference was .58 seconds.


Variables that could have effected the results may have been the temperature of the tap water. This could have varied during the experiment as the first lot of water could have been warmer than the water take from the tap at the end of the experiment. The initial water might have been more at the temperature of hydrochloric acid. For future experiments, the water could have been put into a conical flask and warmed or cooled to the same temperature as the hydrochloric acid and sodium thiosulphate to give accurate results. The time when the cross disappeared could have also caused the results to vary as this took a lot of staring at the cross and sometimes it was difficult to decide exactly the time the cross had disappeared. Maybe a different colour and shaped mark such as a large red dot on a white tile may have made my judgement of when the mark had disappeared more accurate.





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