The rate of reaction of sodium thiosulphate and hydrochloric acid
Chemistry Coursework
Problem
How do we measure the rate of reaction of sodium thiosulphate and hydrochloric acid, and how does the rate of reaction change as the independent variable is changed.
I have listed below some of the factors and variables, which I think, can affect the aforesaid problem above.
The temperature of the hydrochloric acid.
2 The concentration of the hydrochloric acid.
Factors/Variables to be investigated.
I have decided to choose how the temperature of the hydrochloric acid will affect its reaction rate with sodium thiosulphate. I decided to choose this because I think that our results would be more precise than if we were investigating the effect of concentration on the rate of reaction with sodium thiosulphate. This is because if we had chosen to do concentration, it would have been very difficult to make sure that we were measuring the correct volume of water to decrease the concentration of the acid. We would have had to have used precision equipment such as burettes, which would have been rather time consuming in the limited amount of time that we have allocated to us.
Independent Variable
I am going to investigate how the temperature of the hydrochloric acid will affect its rate of reaction with sodium thiosulphate.
Dependant Variable
I am going to measure the rate of reaction between sodium thiosulphate and hydrochloric acid.= it takes for the cross to disappear.
Controlled Variables
1 The cross-drawn on paper that we use to see how long it takes for it to disappear when the Hydrochloric acid is added to the Sodium Thiosulphate.
2 The room temperature
3 If we have to carry on our experiment to the next day,
We will try and use the same apparatus that we had used the day before to ensure a fair test.
4 The volume of Hydrochloric acid.
5 The volume of Sodium Thiosulphate.
Prediction
I predict that as we raise the temperature of the acid, the reaction will speed up. This is from experience from past experiments and the collision theory. I also predict that when we raise the temperature of the acid, the rate of reaction will increase. I also predict that as the temperature increases by 10 , the rate approximately doubles. I have conducted an experiment earlier, in which I studied the effect of temperature on the rate of reaction of magnesium and hydrochloric acid. Here is the equation below.
Mg + 2HCl ==> MgCl + H
I found that as we raised the temperature, the time taken for the reaction to take place decreased.
Time (secs)
88
72
36
24
Temp ( )
20
30
40
50
Rate
0.0114
0.0139
0.0278
0.0417
As we can see from the table, as we increase the temperature of the acid, the rate of reaction increases. We know when the reaction is finished because the mixture is cloudy and yellow.
In order to explain this we must look at the collision theory. In order for the magnesium and acid particles to react together,
They must collide with each other.
2 The collision must have enough energy.
This is shown by the drawings below.
The rate of the reaction depends on how many successful collisions there are in a given unit of time. We must also remember that the more successful collisions there are, the faster the reaction. At low temperatures, particles of reacting substances do not have much energy. However, when the ...
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In order to explain this we must look at the collision theory. In order for the magnesium and acid particles to react together,
They must collide with each other.
2 The collision must have enough energy.
This is shown by the drawings below.
The rate of the reaction depends on how many successful collisions there are in a given unit of time. We must also remember that the more successful collisions there are, the faster the reaction. At low temperatures, particles of reacting substances do not have much energy. However, when the substance is heated, the particles take in energy. This causes them to move faster and collide more often. The collisions have more energy, so more of them are successful. Therefore the rate of reaction increases.
I have drawn below a diagram demonstrating how increasing the temperature affects the rate of reaction
I have also discovered that sodium thiosulphate absorbs chlorine, but since hydrochloric acid has such a small % of chlorine, this is a debatable point.
I have below the equation for the reaction of sodium thiosulphate and hydrochloric acid
Sodium Thiosulphate + Hydrochloric Acid ==> Sodium Chloride + Sulphur Dioxide + Water + Sulphur
Na S O + 2HCl ==> 2NaCl + SO + H O + S
I also have drawn a prediction graph for what effect in increasing the temperature will have on the rate of reaction. I predict that my final graph will look similar to this.
Method
Here is a diagram of how we will carry out our experiment below
We will firstly measure out 10ml of acid in our 10ml-measuring cylinder. We will then pour this acid into our conical flask. We will then measure out 50 ml of sodium thiosulphate into our 50ml-measuring cylinder. We will then heat the acid to the desired temperature, and when it has reached the desired temperature, we will switch off the Bunsen and place the conical flask containing the acid unto the cross. When the acid has cooled down to our desired temperature, we will then add the sodium thiosulphate. We are going to observe how long it takes for the sodium thiosulphate to react with the hydrochloric acid. When the sodium thiosulphate has been added to the acid, we start the stopwatch. We will then look down vertically on the conical flask, and observe how long it takes for the cross to disappear. When the cross is no longer visible, we will stop the stopwatch, and record how long it took to react.
Equipment list.
* 1 thermometer.
* 2 beakers, (250ml) one for the sodium thiosulphate and one for the hydrochloric acid.
* 1 10ml-measuring cylinder for the hydrochloric acid.
* 1 50ml-measuring cylinder for the sodium thiosulphate.
* 1 conical flask, (250ml) for the reaction to take place in.
* 1 tripod
* 1 gauze
* 1 Bunsen burner
* 2 heatproof mats, one for the Bunsen, and one for the cross, so when we place our beaker on the cross, the beaker will not scorch the table
* 1 stopwatch
* 2 pairs of goggles
We will also need at least 500ml of hydrochloric acid and 700 ml of sodium thiosulphate.
Safety
In doing this experiment we will have to take certain safety precautions. Since we are working with acid, we will both wear goggles to protect our eyes. We will not heat the acid any more than 70 because then it would start to boil, and become a safety hazard. We will also make sure that all bags and stools are safely under the tables to prevent anyone falling over them and hurting him or herself. We will also make sure to wipe up any spillages of acid with paper towels.
Result Strategy
To ensure that our results are reliable, we are going to repeat our experiment and continue testing each result remains the same. I have drawn below a replica of the table, which we will be using to record our results on.
Temp of HCl
( )
Time
( )
Rate
( )
20
30
40
50
60
As you can see from the above we have decided that the range of variation for our independent variable is between 20 and 60 . We have decided to move up in units of 10 . This is because it would be too time consuming to move up the scale in units of 5 . When we move up in units of 10 , it will give us a more accurate reflection of how the increase in temperature affects the reaction rate. I am going to put my results in graph form, so we can easily interpret what happens when the temperature increases. This type of graph is shown in my prediction graph above
Interpreting and evaluating evidence.
Here are the results of our experiment below.
Temp of HCl
( )
Time
( )
Rate
( )
20
29
0.0345
30
24
0.0417
40
21
0.0476
50
6
0.0625
60
4
0.0714
We had got the result of 14secs for 60 which we thought was to high so we repeated this temperature until we got a result that stayed the same for two repeats, until we achieved concordant results. We found out that when we repeated 60 , we got the time of 13secs. This result stayed the same when we repeated a second time. We also repeated the result for 50 , because we thought that it was to high a time as well. When we repeated, we discovered that the result stayed the same as the original, so our original result was correct. We also decided to repeat 40 and 30 because we though that it would be wise to achieve concordance. When these results were repeated, we found out that they stayed concordant after one repeat, so they are correct. Here is our final table with our altered results below.
Temp of HCl
( )
Time
(secs)
Rate
( )
20
29
0.0345
30
24
0.0417
40
21
0.0476
50
6
0.0625
60
4
0.0714
Presentation of Data
I have decided to present my results in the form of a line graph, with a line of best fit. When I drew my line graph with a line of best fit, I noticed that there was a sudden leap between 20 and 30 and 50 and 60 .
In noticing this, I decided to draw a second graph, only this graph instead of having a line of best fit, would have a curve. I have noticed that my graph is a linear relationship. I have also noticed that when the temperature rises so does the rate of reaction.
Conclusion
In conclusion, I can see that there is a definitive pattern in my results. I can see that as the temperature of the acid rises, the time taken for it to react with the sodium thiosulphate drops. I have also noticed that as the time falls, the rate of reaction increases. I have decided that the temperature of the acid is in proportion the rate of the reaction i.e. this means that as one rises, so does the other. I have also decided that when we raise the temperature of one of the independent variables in a reaction, the reaction will speed up and the rate of reaction will increase. To explain this we must look at the collision theory. In order for the hydrochloric acid and sodium thiosulphate to react,
They must collide with each other
2 The collision must have enough energy.
The rate of a reaction depends on how many successful collisions there are in a given unit of time, and the more successful collisions there are, the faster the reaction. At low temperatures, particles of reacting substances do not have much energy. However, when the substance is heated, the particles take in energy. This causes them to move faster and collide more often. The collisions have more energy, so more of them are successful. Therefore the rate of reaction increases. I have shown below in two diagrams how the collision theory works. One diagram shows how the collision theory occurs, and the other shows how temperature affects the rate of reaction.
I am pleased that my results agreed with my prediction that as the temperature was raised, the time taken for the acid to react with the sodium thiosulphate dropped. I am also pleased that my prediction that as the temperature was increased, the rate of reaction was increased. I noticed that one of my predictions did not come true. I predicted that as we raised the temperature by 10 the rate of reaction would double. This did not come true as can be seen in my results table above. I think that this is due to the fact that we were not using precise measuring equipment to measure out the acid and sodium thiosulphate, and experiments that have demonstrated the fact that as the temperature is raised by 10 the rate is doubled have been carried out under strict laboratory conditions to ensure a fair test, and these experiments would have used precision equipment. This factor is the main cause why by prediction did not come true. I can safely say that my results are reliable, because we repeated the majority of our results until they were concordant, and this gives us increased reliability. Since I have carried out the aforesaid repeats, this will give my results increased reliability and I can stand over my conclusion that as the temperature rises, the rate increases, and as the temperature of the acid was raised, the time it took to react with the acid dropped.
Evaluation
If I were going to carry out this experiment again, I would make some improvements.
. I would measure out the acid and sodium thiosulphate using a measuring burette instead of a measuring cylinder.
2. When heating the acid, I would use a thermostatically controlled water bath.
3. I would use distilled water to rinse out the conical flask.
4. I would use a more accurate stopwatch, one that measured in milliseconds.
5. I would use a data logger to record my results, like the one I have drawn below. This would give me a more accurate result.
In doing this experiment, I encountered some minor problems. I discovered that once we had heated the acid to the desired temperature, the temperature continued to rise, going up by as much as 30 over the desired temperature. In order to counteract this, we had to place our conical flask containing the acid, under a tap after it was heated to cool it down quickly. We also had a problem in lifting the acid, which had been heated in the conical flask, unto the cross, without burning ourselves. In order to counteract this we used a pair of tongs to lift the hot conical flask.
I have decided that if I were repeating this experiment again, I would raise the temperature by 5 intervals instead of 10 intervals. This would give me a more accurate result and a more true reflection of how the rate of the reaction is in proportion to the temperature.