Also in some cases it is easier to pour solution in to some apparatus then it is with others because is depends on how narrow the opening is, for example solution would be harder to pour into a small conical flask because the opening is a lot narrower than a larger flask.
In addition, it depends on how large the cross is on the paper, and where it is placed. If the cross is changed and it is lighter then obviously the time would decrease as it would be easier for the reaction to cover. If the cross was placed on the bottom, the time would be greater then if the cross was on the side because the thickness that you would be seeing through is different and therefore time different will be very different.
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Temperature : - Increasing the temperature always increases the rate of reaction. In solution the particles are constantly moving. By increasing the temperature the particles move faster because they have more energy. They collide faster therefore the collision frequency goes up.
Because more particles have more energy, a higher proportion will have equal to higher than the activation energy, therefore the successful collision frequency also increases. In addition, when a molecule collides with another particle it transfers its energy to the other particle, is this particle is hit constantly then it should obtain more energy than then the activation energy and therefore reacting.
This is why a slight increase in temperature could affect the rate of reaction. Therefore I must use the same temperature. I will be conducting all of my experiments at room temperature, so there will not be a significant difference in the temperature.
Hypothesis: -
Prediction: -
I predict that as the concentration of sodium thiosulphate increases the rate of reaction will increase.
Explanation: -
This is because as the concentration increases more S2O32- ions will come in contact with H+ ions, this because there will be more S2O3-2 ions. This can explained via collision theory. When two particles collide they need a certain minimum energy called the activation energy, if they have equal to or more than this energy, there will be a successful collision. If the particles have less then this amount of energy they will simply bounce apart. Therefore if the concentration increases then more particles will come in contact, increasing the collision frequency. Therefore, there will be more successful collisions and there shall be an increase in the successful collision frequency.
Justification of my predication: -
From this table I expect to find that as the concentration of sodium thiosulphate goes up, the time of reaction will go down, and therefore the rate of reaction will go up. The rate of reaction, is the number of sulphur molecules created per second, but is equal to 1 divided by the time; 1/time (s) or it can be written as time (s)-1.
From the graph, I hope to show that there is a trend between the two key variables, which are time and concentration of sodium thiosulphate. I hope that from the graph that my predication is correct. I also want to prove that as the concentration of sodium thiosulphate increases the rate of reaction increases.
In the time graph the line is curved and gradually decreasing. In the rate graph, I predict that the graph is linear.
Preliminary Experiment: -
Apparatus:
- 100ml and 250ml conical flask.
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Two 50cm3 and one 10cm3 measuring cylinder.
- Stop watch.
- Sodium thiosulphate
- Hydrochloric acid.
- One sided stick label
- Thick marker pen.
Method:
- Make sure the experiment is not close to the window or anything that could change the temperature, because if the temperature changes, the results could be affected.
- Wash all the apparatus out, so ensure that there is no contamination, when the reagents are poured in.
- Take a one sided sticky label, and with a thick marker draw a cross on the sticky side, then stick this label on the bottom of the conical flask.
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Measure 5cm3 of sodium thiosulphate in the 10cm3 measuring cylinder.
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Take the same measuring cylinder and fill up to the 30cm3 mark with water. Then pour all of the contents into conical flask.
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Take 10cm3 measuring cylinder and measure 10cm3 of hydrochloric acid.
- Pour this into the conical flask and immediately start the stopwatch.
- When the cross is not visible when looking from above the conical flask, then stop the timer and record the time on the table.
- Wash out the apparatus as not to cause any contamination for the next time, so that there are chemicals left, which could affect results.
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Repeat steps (a) – (f), but using 25cm3 of sodium thiosulphate, then repeat steps (a) – (f) again, but using 30 cm3 of sodium thiosulphate, these large amounts can be measures out in a 50 cm3 measuring cylinder.
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Repeat steps (a) – (g) using 5cm3 instead of 10cm3 of hydrochloric acid. Then repeat steps (a) – (g) again using 15cm3 instead of 10cm3 of hydrochloric acid.
- Repeat steps (a) – (g), but change the concentration of hydrochloric acid, and keep the concentration of sodium thiosulphate constant.
Results
Green – using 10cm3 of HCl.
Blue – using 5cm3 of HCl.
Red – using 15cm3 of HCl.
Yellow- varying the concentration of HCl, instead of Na2S2O3
Graphs, when varying the concentration of Sodium Thiosulphate
These graphs show that as the concentration increases the rate of reaction increases.
These graphs, show that as the as the concentration increases there is a gradual decrease in the time taken for the reaction.
Graphs, when varying the concentration of Hydrochloric acid
This graph shows that as the concentration increases there is a gradual decrease in the time taken for the reaction. From this I can determine that, if there is an increase in the concentration of hydrochloric acid, then the time may be affect, as it will decrease and be lower, therefore disturbing my results.
These graphs also show that as the concentration of hydrochloric acid increases the rate of reaction increases, and because this is a controlled variable, therefore a slight increase or decrease in the concentration could have a large affect on the results.
Sources of Error
For the first experiment I used a small 100cm3 conical flask, this was hard to pour into as the opening was narrower, therefore when pouring the hydrochloric acid, I had to pour slowly, which may have effected the results as I was timing, the experiment. Therefore for the rest of the experiments I used a 250ml conical flask which was easier to pour with. In the actual experiment I will use a 250ml conical flask, which will be easier to pour into and I will be able to get more accurate results.
I used three different volumes of HCl to see which one had more a suitable range, so that the time was not too short or too long. I shall use 10cm3 if hydrochloric acid because 5cm3 had a time which was close to 3 minutes, while 10 and 15cm3 had their longest times closer to 2 minutes. The results between 10cm3 and 15cm3 are not very different, this is because we are only measuring the experiment until the solution goes opaque, therefore there is an excess amount of HCl, because we don’t need an excess, I will use only 10cm3 in the experiment.
The results could have been affected by the variable, temperature, which can have a large affect even if this does not raise much. My preliminary experiment has helped me to decide that I will try to keep this constant. I will conduct all my experiments on one day, so that the temperature will be closer together. In addition, I will keep the experiment away from any doors, windows, flames or radiators which may have may have an affect on the results.
Safety:
We will be using very low concentrations so there will be no hazards with the chemicals. However, in case any glass is broken, immediately clear up, and dispose of in the broken glass bin, not the ordinary. Consult the teacher of any injuries or accidents.
Apparatus
- 250ml conical flask.
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Two 50cm3 and two 10cm3 measuring cylinder.
- Stop watch.
- Sodium thiosulphate
- Hydrochloric acid.
- One sided stick label
- Thick marker pen.
Method
- Keep experiment away from anything which could change the temperature of the experiment and affectively change the results.
- Wash out apparatus, as not to cause contamination.
- Take a one sided sticky label, and with a thick marker draw a cross on the sticky side, then stick this label on the bottom of the conical flask.
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Measure 5cm3 of sodium thiosulphate in the 10cm3 measuring cylinder and pour into a 50cm3 measuring cylinder.
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Take the same measuring cylinder and fill up to the 30cm3 mark with water. Then pour all of the contents into conical flask.
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Take another 10cm3 measuring cylinder and measure 10cm3 of hydrochloric acid.
- Pour this into the 250ml conical flask and immediately start the stopwatch.
- When the cross is not visible when looking from above the conical flask, then stop the timer and record the time on the table.
- Wash the apparatus completely, as to not cause any contamination.
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Repeat steps (a) – (f), each time increasing the amount of sodium thiosulphate by 5cm3 until 30cm3. Therefore, we have a range of 5, 10, 15, 20, 25 and 30cm3.
- Repeat steps (a) – (g) three time, so can have an average result at the end, and the number of errors reduced and therefore we have more accuracy, by dealing any anomalies.
How to control variables that could affect my results.
I will make the test fair, by controlling the person using the stopwatch, which will be me; therefore my reaction time will stay the same and therefore reducing errors. I will clean out the apparatus each time, so that the apparatus is not contaminated, also I will use the same apparatus. Temperature is very hard to control, I can not make sure that it is exact, but the experiment will happen under room temperature, which will be about 22 oC, and I will keep my experiment away from anything, which could potentially heat up the experiment, e.g. Bunsen flames and radiators. The concentration of HCl will be the same, as we will not be making the concentration, but be provided with it. The volume of hydrochloric acid, we can measure to the closest 0.5 cm3, there will be a little amount of error, but not much.
This is how I will record my results.
In addition, I will create a scatter graph for time against concentration of sodium thiosulphate, and draw a best of best fit. I will also draw a scatter graph of rate of reaction against sodium thiosulphate, with a line of best fit.
