After doing my preliminary experiment I have chosen to use 5cm of hydrochloric acid and 15cm of sodium thiosulphate. My range of experiments will be from 20 degrees Celsius to 70 degrees Celsius. (All of these temperatures will be used going up in steps of 10 degrees.) Also after doing my preliminary experiment I have chosen what apparatus will be necessary to use, during the investigation.
1 thermometer
1 beaker
2 measuring cylinders
1 conical flask
1 stopwatch
X board
1 pair of goggles
Water bath
Method.
5cm of hydrochloric acid and 15cm of sodium thiosulphate will be poured into two measuring cylinders. If I am heating the two solutions to a higher temperature I will place them both into I water bath of the correct temperature. When they are heated to the correct temperature (this will be measured by using a thermometer) I will pour the two solutions into c conical flask. The time it takes the x to disappear is timed and recorded. The experiment is then repeated using all the different temperatures. The whole entire experiment will be then repeated a further 2 times. Repeat results and averages will be taken to improve the credibility of the findings, and present solid grounding for the final conclusion. The repeat results will help to iron out any anomalies and the average will give a good summary of the results of the experiment. However if one set of results is entirely different to the other, a third experiment will be performed to replace the anomalous set of results.
Safety – A pair of goggles will be worn during the heating part of the experiment in order to protect the eyes.
Fair Test - In order for my findings to be valid the experiment must be a fair one. I will use the same standard each time for judging when the X has disappeared. I will make sure that the measuring cylinders for the HCl and thiosulphate will not be mixed up. The amount of HCl will be 5 cm3 each time, and the amount of thiosulphate will be fixed at 15 cm3.
Prediction
I predict that as the temperature increases the rate of reaction will also increase. This is because as there is a ten degrees rise in temperature the reaction time will half. This means that when I draw my graphs they will both have a positive correlation, and will probably be curved as the increase in the rate of reaction will not be the same as the temperature is increased. This can be justified when relating to the collision theory; when the temperature is increased the particles have more energy and thus move much faster.
Obtaining evidence
Temp. (ºC) Time 1 (s) Time 2 (s) Time 3(s) Average (s)
20 110.67 107.42 109.04
30 100.13 103.34 101.73
40 64.20 65.92 65.06
50 45.34 37.73 41.53
60 30.12 33.18 31.65
70 18.92 16.34 17.63
Analysis
In this experiment I have found that as the temperature is increased the time taken for a reaction to take place decreases. This means that the rate of reaction increases as it takes less time for a reaction to take place. This can be related to the collision theory. In the experiment the time taken for a reaction to take place decreased by roughly 10 to 15 seconds for every 10ºC increase in temperature, with the one anomaly being the 30ºC reading
When I have plotted a line of best fit into my graph I can draw a conclusion from my experiment Firstly I can see that with the” graph (that plot temperature against time taken for the reaction to take place) the graph has a negative correlation.
This means that when I plot a graph with rate against temperature it has a positive correlation – as the temperature is increased so does the rate of reaction. This is because when the temperature is increased the particles will have more energy and thus move faster. Therefore they will collide more often and with more energy. Particles with more energy are more likely to overcome the activation energy barrier to reaction and thus react successfully, and when solutions of reacting particles are made more concentrated there are more particles per unit volume. Collisions between reacting particles are therefore more likely to occur.
My graph shows that the difference of rate between increasing temperatures (excluding the anomaly of 30ºC) was increasing in steps of 6-10 (9.17 to 15.37 to 24.28 to 31.67). However, once again there is a giant gap in the last temperature increase – at 60ºC the rate of reaction is 31.67 and at 70ºC it is 57.03.
For a reaction to occur particles have to collide with each other. Only a small percent result in a reaction. This is due to the energy barrier to overcome. Only particles with enough energy to overcome the barrier will react after colliding. The minimum energy that a particle must have to overcome the barrier is called the activation energy, or Ea. The size of this activation energy is different for different reactions. If the frequency of collisions is increased the rate of reaction will increase. However the percent of successful collisions remains the same. An increase in the frequency of collisions can be achieved by increasing the concentration, pressure, or surface area.
(Last paragraph internet source. www.chemguide.co.uk)
