PLAN for the investigation into the affect of the concentration of Sodium Thiosulphate on its rate of reaction with hydrochloric acid.
Chemistry- PLAN for the investigation into the
affect of the concentration of Sodium Thiosulphate
on it's rate of reaction with hydrochloric acid.
Rates of reactions are affected by four main factors of reactants which are the size of the particles of the reactant, the temperature of the reactant, the concentration of the reactant and adding a catalyst into the solution. As shown by the title the main one which will be focused on in this planning and experiment is the concentration of the solution of sodium thiosulphate. This affects the rate of reaction as the more concentrated reactant 1 is the more particles of the acid there are which come into contact with reactant 2, and then this means more particles from reactant 1 are reacting with reactant 2 and so this means the rate of the reaction is faster.
APPARATUS: DIAGRAM:
60cm3 of sodium thiosulphate
10cm3 of water
5cm3 of hydrochloric acid at 1M
Measuring Cylinder
Beakers
Conical Flask
Paper with X
PREDICTION:
So my above information on the rate of reactions to do with concentration concludes my prediction, as, my prediction is the more concentrated the sodium thiosulphate the more faster the reaction between the sodium thiosulphate and hydrochloric acid will be. I think this will be the case because as shown above the more concentrated the thiosulphate is the more particles of it there will be that react with the hydrochloric acid, so this will make a faster reaction and make the cross disappear faster aswell. Because when the sodium thiosulphate particles will react with the hydrochloric acid I think this will make the solution block out the cross quicker due to the no. of particles of sodium thiosulphate reacting with the acid being larger. Also preliminary work was done and this supports that the more concentrated a solution the faster a reaction and this is shown in my preliminary results and graph below in my preliminary work.
Preliminary Work:
The preliminary work was carried out using a simulation off the computer. This was utilized by there being controls on the amount of sodium thiosulphate and water, which were altered each time by 10cm3 to equal 50cm3 always and this was for the change in concentration, the amount of hydrochloric acid, which stayed the same as 5cm3 at 1M, the time was measured to see when the cross would disappear and this time was noted each time, and finally the temperature was controlled to stay at 20ºC throughout this experiment. The graph and results from the investigation of ...
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The preliminary work was carried out using a simulation off the computer. This was utilized by there being controls on the amount of sodium thiosulphate and water, which were altered each time by 10cm3 to equal 50cm3 always and this was for the change in concentration, the amount of hydrochloric acid, which stayed the same as 5cm3 at 1M, the time was measured to see when the cross would disappear and this time was noted each time, and finally the temperature was controlled to stay at 20ºC throughout this experiment. The graph and results from the investigation of the simulation in this preliminary work is shown below.
RESULTS:
Volume of sodium thiosulphate
Volume of water
Conc. Of sodium thiosulphate
Time taken(Secs)
Rate of reaction(1/TIME Taken) (2sfg)
50
0
0.1
87
0.011
40
0
0.08
20
0.0083
30
20
0.06
53
0.0065
20
30
0.04
240
0.0042
0
40
0.02
595
0.0017
This is showing the higher the concentration the faster the rate of the reaction.
GRAPH:
EQUATIONS:
Sodium Thiosulphate + Hydrochloric acid ? Sulphur + Sodium Chloride + Sulphur Dioxide + water
Na2 S2 O3 (aq) + 2HCl (aq) ? S (s) + 2NaCl (aq) + SO2 (g) + H2O (l)
METHOD
The way the experiment was carried out is the apparatus will be setup as shown in the diagram. A sheet of paper with an X in the middle was placed under a conical flask with the X being under the conical flask. Then sodium thiosulphate was taken and poured into a measuring cylinder and measured to 160cm3(150cm3 is just needed but 160cm3 just incase) and poured into a beaker for all of the sodium thiosulphate needed, and water was taken and poured into another measuring cylinder to measure about 110cm3( again only 100cm3 is needed but just in case).
The volume of thiosulphate added to water is a controlled variable in this investigation as it's being controlled at 50cm3 for all the investigation. The volume of thiosulphate is an independent variable as it's being changed by me where I will be decreasing 10cm3 of it every experiment. And the volume of water is an independent variable as that is also being changed by me where I will be increasing it by 10cm3 every experiment so when it's added to the sodium thiosulphate it equals 50cm3.
For the first measurement 50cm3 of sodium thiosulphate with no water was poured into the conical flask by measuring it firstly in the measuring cylinder, after that by using the measuring cylinder 5cm3 of hydrochloric acid with 1M of concentration was poured and reacted with the sodium thiosulphate and a stopwatch was used to time how long it took for the X to disappear and then this was noted. The hydrochloric acid in this experiment is a controlled variable as it's being controlled and not going to change, so it will stay at 5cm3 at 1M, and the time/rate of the reaction that makes the X disappear is a dependent variable as this variable's outcome depends on the independent variable and it's going to be measured by me. Additionally the environmental temperature is a controlled variable as the temperature at which the experiment will be done is at room temperature and that will be kept constant.
Also this experiment was repeated by using the other sodium thiosulphate from the beaker but firstly the beaker was rinsed out to get rid of cross contamination. Then sodium thiosulphate was poured into the beaker but 10cm3 less from the previous experiments were poured into each experiment followed by another. But before it's poured into the conical flask the water is poured into it to lower
the concentration. And the amount of the water in each experiment was the amount which when added to the amount of sodium thiosulphate equals 50cm3, and this again was measured using the measuring cylinder. Then the rate of the reaction was noted as well by doing 1/TIME taken for the cross to disappear. This investigation was repeated one or two more times to get better results and check to make sure no result was way out, it also gets an average.
Obtaining Results
RESULTS:
Volume of Sodium thiosulphate
Volume of Water
Concentration of sodium thiosulphate
Time taken(secs)
Expt 1 Expt 2 Average
Rate of reaction(1/TIME taken) (2sf)
50
0
0.1
43
41
42
0.024
40
0
0.08
50
52
51
0.02
30
20
0.06
64
66
65
0.015
20
30
0.04
99
01
00
0.01
0
40
0.02
215
213
214
0.0047
GRAPH:
Graph 1-
Graph 2-
Analysis & Evaluation
ANALYSIS:
Graph 1 is linear and proportionally increases, and this is similar to the graph in my preliminary work as that is linear and proportionally increases. These graphs can only be proportional if the starting co-ordinate is at(0,0), and we know when hydrochloric acid is added to only water it has no reaction, as at a concentration of 0 the rate of reaction is 0. So this shows these are proportional as they start at the origin. Graph 2 is non linear, non proportional but decreases at a decreasing rate. From Graph 1 it can be seen that as the concentration of the sodium thiosulphate increases the rate of reaction increases. Graph 2 is showing that as the concentration increase the time taken decreases, and this compared to the graph 1 is the same as the lower the time the higher the rate of reaction. But the results I picked up from my investigation were different to the preliminary results, the only similarity being the rate of reaction decreased as the concentration did. The reason for the rate of reaction increasing as the concentration increases is because of the concentration theory. Which is, when there's a higher concentration there are more particles of the sodium thiosulphate, and so there are more sodium thiosulphate particles reacting with the hydrochloric acid so there is a quicker reaction, so there's a higher rate of reaction.
Evaluation:
I think the errors in the experiment which affected the results, and meant the results were different to the preliminary results( as these results were accurate because they were done using a computer under the same conditions like the temperature staying constant), were that the results were never going to be accurate because it would be hard to stop the watch straight when the cross has disappeared because of reaction time, and eyesight could affect it. Because, bad eyesight could think the cross has disappeared when there is actually still time for it to disappear. Also I think the experiment doesn't benefit from the environmental temperature, as that employs temperature which changes and can't be kept constant. And heat affects the rate of a reaction, so even if the environmental temperature isn't kept constant the results won't be accurate. Additionally human error in measuring out the water, sodium thiosulphate and hydrochloric would affect the outcome of the results as well as it would make them inaccurate. Lastly cross contamination may have also occurred through not washing the equipment after needing to put other solutions into it.
The improvements which would improve the end results and make them similar to the preliminary results are doing the whole experiment under the same conditions of temperature, so do it in a room where the temperature is always constant so this won't affect the rate of reaction and so the results. Also making sure eyesight is good so make sure the goggles worn aren't affecting whether the cross can be seen or not, make sure glasses which are worn are glasses which make the eyesight see fully and make sure glasses are worn if need be to improve the eyesight, and this makes the results more accurate. Lastly making sure the equipment is washed and the contents of it is emptied only when different solutions are needed to be put into the equipment, so this gets rid of cross contamination so it won't affect the results. Or having different equipment, where there is equipment for each solution, so the measuring cylinder and beaker for each. This can differentiate between which solutions are to which equipment and not getting confused between thinking was this solution in here or this one, which is done by having the contents of the solution in a beaker with a label of its solution. This gets rid of any cross contamination coming in and there is no need for washing except washing the conical flask, and also pouring the solution out of the measuring cylinder is needed to be done so other volumes of the solution can be measured.
