The acid particles are randomly moving in the water. As you increase the concentration of the acid, therefore there are more acid particles in the same volume. The frequency of collisions between the two reactants increase, therefore the rate of reaction increases.
The factor I’m going to considered in investigate and observe is how temperature affects the rate of a reaction. I will investigate the changes caused to the solution of hydrochloric acid and sodium thiosulphate when the temperature is increased slightly each time I attempt the experiment.
Changes in temperature change the kinetic energy of the particles and the number of successful collisions increase. This involves two types of theories, the kinetic and collision theory. The kinetic theory states if the movement of particles in a substance increased particles have gained energy, they move around faster colliding with each other this falls in the collision theory. This means if temperature increases, the rate of the reaction increases as well.
Prediction
As I have explained, the rate of a reaction is the speed at which it takes place. Temperature is a major factor in this as temperature increases or decreases, this affects the movement of particles in a substance therefore, and this causes the rate of the reaction to change. When a reaction is heated up, each particle requires energy for the particles to collide.
- The temperature here is 30 ºC
-
Here the temperature is 40 ºC
Predicted graphs
As you can see from my research, that if the temperature is increased, this will increase the speed at which particles react and therefore the reaction becomes faster.
In this experiment of sodium thiosulphate and hydrochloric acid, I also predict that my results will decrease as the temperature increases.
This shows that as the temperature increases the rate of the reaction decreases.
Plan
I will measure out an accurate amount of sodium thiosulphate solution using a conical flask and add it to a solution of hydrochloric acid. As soon as these two solutions are added together, I will time how long it takes to form a precipitate and a cloudy solution. I will lay a paper with a cross on it under the flask of solution and time precisely how long the mixture takes for the cross under the beaker to disappear. This experiment will be conducted twice but by varying the temperature if the sodium solution each time to see how the rate of the reaction changes.
The diagram of the experiment is shown below:
There are other ways to conduct this experiment:
OR like this:
However, I will be using this method. As I think it is the most appropriate way to see how temperature can be measured in a rate of a reaction.
Fair Test
In order to conduct my experiment, I will have to observe that my experiment is carried out fairly. This will include the factors that may affect this rate, to keep them the same each time I carry out this experiment. I carry out this in the same conditions at room temperature.
Also I will make sure the factors that I mentioned before will be kept the same each time. I should also keep the surface area the same and not change the size of my beakers or conical flask, as this can cause a major change in the results. I will make sure that my temperature is kept constant otherwise it will not be a fair test. Each time I carry out this experiment I will use the same equipment and keep my factors the same.
To make my results fully accurate I will take two sets of readings and then I will work out an average reading of my results. I will take an accurate reading of the temperature because it is very necessary I don’t measure an incorrect reading because this investigation will not be a fair test.
Safety
Throughout this experiment I will make sure that everything is safe, even before I start it. I will wear goggles at all times and wear a alb coat to prevent any chemicals from getting on my clothes. I will always use a heat proof mat and a tripod whenever I use the Bunsen burner and take great caution of turning it on. I will also take precaution when handling with anything hot so I don’t injure myself.
Apparatus
- Sodium thiosulphate solution
- Hydrochloric acid
- 250 ml conical flask
- thermometer
- measuring cylinder
- heat proof mat
- Bunsen burner
- Tripod
- Gauze
- Stop clock
- Plain with paper with a black cross, laminated.
Method
Firstly, I will take some of sodium thiosulphate in a conical flask and choose an appropriate temperature to begin with I will most likely be choosing 20º C. At this point, I will add 5 cm of hydrochloric acid using a measuring cylinder, into the beaker of sodium thiosulphate; which I will place on the black cross.
When the two substances are added together, I will immediately start the stop clock and time how long it takes for the black cross to disappear. To heat up the sodium thiosulphate I will use a Bunsen burner to heat it up at different temperatures, according to the temperatures I choose. Each time I stop the clock I will record the results in a table. After collecting these results, I will work out an average and create a graph, to see a pattern of how the temperature affects the rate of a reaction.
In the experiment of sodium thiosulphate and hydrochloric acid they react together to form a precipitate or sulphur and form spectator ions.
Sodium thiosulphate + hydrochloric acid → sodium chloride + carbon dioxide + water
Na2 S3 O3 (aq) + 2HCL (aq) → 2NaCl (s) + S (s) + SO2 (g) + H2O (aq)
The ions that take place in the reaction are:
IONIC EQUATION
S2O3 ²- (aq) + 2 H+ (aq) → S (s) + SO (g) + H O (aq)
The ions that don’t take part in the reaction are the spectator ions, they are:
SPECTATOR IONS
2Na+ (aq) + 2Cl- (aq)→ 2NaCl (s)
Preliminary work
Preliminary work is done to get an understanding of how the actual experiment will b conducted, to see what variables could affect the rate of the reaction.
In the experiment I did the appropriate method I mentioned before, using the correct amount of solution and heated it up at the appropriate temperatures and place it over the black cross and time how long it takes for the black cross to disappear. I recorded 7 sets of readings of different temperatures theses are the results I collected.
Results
From the results above I can see the overall experiment worked as I had expected. The readings are fairly reasonable and I haven’t had any anomalous results. This proves that my experiment was accurate.
I believe the preliminary experiment is very useful. It has helped me understand a lot of things for how to measure a rate of a reaction and the factors that affect it. This investigation will help me decide how to improve this experiment in my actual one. However, I feel that I am satisfied with my experiment that I have planned and I don’t feel I need to change or improve my experiment.
From this graph I can see that there is a negative correlation. This shows my prediction was quite accurate. As the temperature increase, the less time it takes for the black cross to disappear therefore the reaction rate speeds up.
Obtaining Evidence
For this experiment, I conducted it three times, in order to give me more accurate results. The results to my experiment are tabulated below:
From these sets of results I will create an average result graph showing the outcomes. I will record the average results as it makes the experiment a fair test.
This graph shows negative correlation which proves my prediction is correct. As the temperature increases the average time taken decreases, this is due to the collision theory.
Now I will find out the rate of the reaction in this experiment. To find out the rate I will follow the formula and use my results to find out what the rate is:
To find rate: 1 (g)
Average time (s)
From these results I will now create a graph showing the rate of the reaction.
This graph shows positive correlation, which shows my prediction, was correct, this proves that as the temperature increases the rate of the reaction increases as well this is also to do with the collision theory.
Analysing
All my experiments have visible results, to find the rate of the reaction is no exception. During, the experiment when I added the hydrochloric acid to the flask, I observed immediately each time to see any change taking place between the temperatures. When observing the experiment, the changes that take place were mostly due to the changes in different temperatures of sodium thiosulphate and hydrochloric acid. The initial temperature which was the lowest, the solution became very foggy and misty but this took quite a long time. As the temperature increased, it took less time for the solution to become foggy until it was no longer clear and the cross couldn’t be seen. The solution had changed colour from a clear liquid to a pure white milky solution.
Observing my results, I notice that there is a considerable difference from the lower temperatures to the higher temperatures. Therefore, this means the higher the temperature, the faster the rate of the reaction. If I look at the results for the rate of the reaction I notice that each time my reaction had doubled. From 20 ºC to 30 ºC the rate went from 2 to 4 ×10 -2. However, there was one exception the rate didn’t double when the temperature went from 40 ºC to 50 ºC because the rate went from 7 to 12 ×10 -2. Although, when the temperature reached 60 ºC to 70 ºC the rate doubled again, as it went from 19 to 29 ×10 -2. This must have occurred due to the timing of the reaction, as I must not have pressed the stop clock in time when the reaction was occurring.
Overall I feel that my results are fairly accurate, which proves my prediction, my experiment was quite successful because there is no anomalous results. Also, my graphs seem to match my prediction graphs, my results table and graph show as the temperature increases, the time for the cross to disappear becomes faster.
My experiments seem to have proved my prediction, which is that as the temperature increase, the particles gain more energy which collides faster and harder, causing more collisions therefore the reaction becomes faster linking my results to my prediction.
When the hydrochloric acid was added to sodium thiosulphate a deposit of sulphur was forced, this was what made the solution cloudy and made it impossible for the black cross to be seen.
Sodium thiosulphate + hydrochloric acid→ sodium chloride +sulphur + carbon dioxide+ water
Evaluation
After conducting this experiment I think the investigation went well and I found it was a simple and straightforward process to carryout. I believe that my results were reasonably accurate standard and I had no difficulties in following the method or using the equipment. By conducting the experiment three times I think this helped me because it gave me more reliable and precise results, which lead me to find the average results this, made the experiment a fair test. Therefore, when I plotted my results on a graph it clearly proved how accurate my results were.
As you can see in my experiment, there are no anomalous results this is due to the caution and carefulness that I put into making sure that the experiment was set up correctly with precise measurements of chemicals and substances. To show how accurate my results are I will plot all my results from the three attempts of my investigation on to one graph and draw a line of best fit. This will enable me to see how accurate y results are. Also it will prove whether there is a trend or not.
From the results on my graph, I can see that when all the results are plotted, they show negative correlation this tends to prove the accuracy of my experiment. Also, at the lower temperatures, the time for the cross to disappear was less, because the particles did not have as much energy as they did at the higher temperatures. At these temperatures the particles collide with much more energy and therefore the reaction takes much less time to produce sulphur which increases the rate at which the cross disappears.
To make my results more detailed I would have repeated the experiment a few more times. Although the experiment was repeated three times, I still feel I should have carried this further to get more accurate results. However, the time I was given didn’t allow me to do so. So I would consider this as an improvement, of what I would do if I had to repeat this experiment again.
I only recorded my temperatures up till 70 ºC, which I feel was fairly reasonable to see how temperature affects the rate of a reaction. However, I believe I could have recorded results of much higher temperatures as well to see the change in the rate, though this could have been dangerous so I can’t really say I would improve this area.
Overall I think my experiment has been successful, and reliable under the time which was allocated. Though, I do feel with more time I could have repeated the experiment and made it further accurate. In this experiment, temperature was my focus and I am able to draw a conclusion that, when the temperature increases the rate of the reaction takes decreases.
In the experiment I didn’t use any device to help me in my investigation, though to improve my experiment I could use a different method to perform the experiment. Instead of using my eye to measure the results, I could use a device to help me in my investigation to measure the rate of a reaction. The apparatus I would use equipment called a data logger. This will help me measure the rate accurately.
A data logger is an electronic instrument that records measurements including (temperature, relative humidity, and light intensity, on/off, open/closed, voltage, pressure and events) over time. The data logger is connected to a personal computer.
The logger records each measurement and stores it in memory with the time and date. The logger is then connected to a personal computer and the software is used again to readout the data and see the results as a graph. Data loggers features the latest in digital technology which makes them smaller, less expensive, more accurate and more reliable than chart recorders. Therefore, it is an improved and more sufficient way of measuring the temperature, and would help me produce adequate results, compared to using my eyesight.
