The acid particles move randomly through the water, as you increase the concentration of the acid, there are more acid particles in the same volume. The frequency of the collisions between the two reactants increases, as in the collision theory, and the rate of reaction increases.
The factor I have considered to investigate and observe is how temperature affects the rate of a reaction. I’m going to investigate the changes caused to the solution of hydrochloric acid and sodium thiosulphate when the temperature is varied 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 kinetic theory and collision theory. In the kinetic theory it states if the positioning and movement of the particles in a substance increases if the temperature increases. Therefore, increases the temperature increases the energy between the particles and makes them move around a lot more and collide often with other particles; this falls into the collision theory. Hence, if temperature increases, the rate of reaction increases.
Prediction
As I have explained, the rate of a chemical reaction is the speed at which it takes place. Temperature is a major factor in this as increase or decreases of temperature changes the movement of particles in a substance, therefore changing the rate of reaction. When a reaction mixture is heated up, each particle acquires more energy and collides more with other particles. E.g.
Reaction at 30 º C Reaction at 40 º C
Consequently from my knowledge and research I can make the prediction that if you increase temperature of a particular reaction, you increase the speed at which it takes place. This is simply because the particles carry more energy and collide more often. As temperature is raised particles are moving faster and collide with greater power, the reaction becomes faster.
In the experiment of sodium thiosulphate and hydrochloric acid, they react together to form a precipitate of sulphur, and form spectator ions.
Sodium thiosulphate + hydrochloric acid → sodium chloride + sulphur + carbon dioxide + water
Ionic equation: the ions that take place in the reaction are-
The ions that don’t take part in the reaction are spectator ions, they are:
Apparatus
Sodium thiosulphate solution stop clock
Hydrochloric acid plain paper
250ml conical flask
thermometer
Measuring cylinders 50cm & 5cm
Heat proof mat
Bunsen burner
Tripod and gauze
A diagram of the experiment is show below:
Add dilute acid and start timing. Time how long it takes for the cross to disappear.
Heat to appropriate temperature and then mix
Two solutions together and again time how long
It takes for the cross to disappear.
Plan
I will measure 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 under the flask of solution and time precisely how long the mixture takes for the cross to disappear. This experiment will be conducted several times but by varying the temperature of the sodium solution each time, to see how the rate of the reaction changes.
Fair test
In order to conduct my experiment fairly I have to observe the factors that may affect how well the investigation will work. This includes factors like using different equipment or doing the experiment in different conditions. Also making sure variables I have mentioned are kept constant throughout, such as the concentration of the solution, the surface area, the amount of pressure exerted, and also any catalyst I use. All of these factors can greatly affect the rate of a reaction. To combat this, I will make sure that upon repeating the experiment, all these factors and equipment I use will be the same and will be kept constant throughout each attempt.
I think these factors are important because they could affect the results severely and lead me with anomalous results, when they should be correlating. To ensure fair and accurate results all the factors that can affect my results need to be controlled.
My independent variable is the temperature as this will be the factor that is changed in each attempt. My fixed variable will be the volume, concentration, surface area and pressure of the sodium thiosulphate and hydrochloric acid. In each experiment an equal quantity of the substance will be used each time, and has to be kept constant as it can alter my readings making the experiment unreliable.
Reliable results
To make my results fully accurate I will take several readings for each result and altogether find an average reading. The temperature has to be calculated accurately as it can be. An incorrect reading can make the investigation void, if one result is not calculated properly. After I have calculated my results I will enter them in a table, as shown below, and then calculate the average readings.
Safety
Throughout this experiment, safety is my number one priority, I will wear goggles at all times, to protect my eyes, and wear a lab coat to prevent any chemical to get on my clothing or on me. I will use a heatproof mat and a tripod when using a Bunsen burner and I will take extreme caution when turning it off and on. I will also consider taking precaution when handling hot flasks to prevent burning or injuring myself.
Method
Firstly I will take 50cm of sodium thiosulphate in a conical flask and then choose an appropriate temperature to begin with most likely 25 ºC, room temperature. At this point I will add 5cm of hydrochloric acid using a measuring cylinder to the beaker of sodium thiosulphate and place it cove the paper with the cross-marked on it.
When these two substances are added together I will immediately measure the time at which it takes for the cross to disappear using a stopwatch. As I will be conducting the experiment at different temperatures I will use a Bunsen burner to heat the sodium thiosulphate each time according to the variable temperatures I choose. Each time I carry out the experiment will recall the timings of how long it took for the cross to disappear in a result table shown previously. After collecting these results I intend to find an average and create a graph. Through this graph I will attempt to find a pattern or trend see how the temperature effects the rate of reaction.
Temperatures I have chosen to test are: -
Using an accurate thermometer I shall be able to measure the experiment at these precise temperatures efficiently.
Preliminary
To understand the investigation thoroughly and to clear what variables could affect the rate of the reaction, I conducted a preliminary experiment to make myself clear, and decide on how the actual experiment will be conducted. In my preliminary experiment I followed the appropriate method by using the correct amount of solution and heated it to an appropriate temperature, then added it to 5cm of hydrochloric acid. I kept the beaker placed over the paper with the cross and timed how long it took for the cross to disappear. I varied the temperature each time I did the experiment, as to follow my aim and by conducting the experiment and taking five readings for different temperatures, these are the results I collected.
From the results I can see the overall experiment worked as I expected. The readings are fairly reasonable, and I have been able to combat any anomalous results. This tends to prove the accuracy of my experiment.
I believe the preliminary experiment was very useful it has helped me decide what method I will use in my investigation, how I plan to set it out and what I need to change to improve the experiment to provide precise results.
Graph to show preliminary results and predicted graph
For the predicted graph for the results, I believe this is approximately what my results will look like when plotted on a graph. The results will slope down with negative correlation.
The preliminary is a way for me to recognise I’m conducting the experiment correctly, and will be prepared for the real one. For the preliminary work I did the experiment but didn’t repeat it, as I only wanted to see that the values I was to be using are accurate. This helped me plan my actual investigation, as I learnt through my mistakes. These were things like not starting the stopwatch quick enough and not using a completely accurate amount of acid. Therefore in the real experiment, I’m going to be careful when measuring chemicals to get them accurate, and start the stopwatch at the exact time the hydrochloric acid is added to again ensure fair and reliable results.
Obtaining Evidence
For this investigation, I conducted this experiment three times, in order to gain more reliable results. From these three sets of results, I will create an average result and show the outcomes on a graph.
The chart below shows the average results plotted on a graph, to show the average speed at which the cross disappeared.
Analysis and observation
All rates of reaction experiments have visible results and this experiment is no exception. When I added the hydrochloric acid to the flask, I observed immediately at each temperature to see the changes or reactions that were taking place between the particles.
When observing the experiment, the changes I saw take place were the tone of the sodium thiosulphate and hydrochloric acid. At the initial temperature which were low, the solution became very foggy and misty but only after a fairly long time. At the higher temperatures the solution became foggy quickly until it was no longer clear or transparent, and the cross could not be seen. The colour of the solution went from a clear colourless liquid, to a yellowish green colour. I did not see any gas given off or any vigorousness in the actual reaction.
Analysis
From my results I notice there is a considerable difference in time for the cross to disappear from the lower temperatures to the higher temperatures. The higher the temperature of the solution, the faster the rate of the reaction. As we increased the temperature the speed decreased for the cross to disappear, therefore proving my prediction. All the times are pretty much the same, or are quite close for the three different recordings, indicating that the experiment was a pretty successful one. There are no anomalies and the average temperatures seem to descend, as the temperatures increase. My results table and graph clearly shows that the time for the cross to disappear decreases as the temperature increases.
From the graph I can see that the gradient shows, that as you increase the temperature every ten seconds the difference of speed at each temperature decreases, this is the pattern that I noticed. The time taken for the sodium to become cloudy takes less time as we increase the temperature of the sodium. My experiment seems to have worked accurately as it proves my prediction is correct. I was right in saying that as the temperature of the solution increases the particles gain more kinetic energy and cause the particles to move faster and cause frequent collisions with greater power, therefore the reaction becomes faster linking my results to my prediction.
When the dilute acid was added to sodium thiosulphate, a deposit of sulphur was formed. The sulphur made the solution cloudy, as more sulphur is formed; the more impossible it is to see through it. The balanced equation for this reaction is below:
Sodium thiosulphate + hydrochloric acid → sodium chloride + sulphur + carbon dioxide + water
From my results I find that if the temperature of the solution is raised, the time for a reaction to occur is decreased. The cross disappeared more rapidly as the temperature rose, and I think this is due to the increase of energy between the particles and the increase of energy between collisions that successfully passed the energy barrier. This released the sulphur quicker and in larger doses, which turned the solution cloudy thus making the cross invisible.
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 are colliding with much more energy and therefore the reaction releases sulphur and releases more sulphur at a much quicker rate at which the cross disappears.
In my initial prediction I stated that if you increase the temperature of a reaction, you decrease the time it takes to occur. Looking back at my results I can see that this hypothesis was correct as the time for the cross to disappear decreased as the temperature rose. The particles were moving around more energy enough to break the energy barrier and for a reaction to occur as the temperature rose.
The rates at which all reactions happen are different. An example of a fast reaction is an explosion, and an example of a slow reaction is rusting. We can measure reactions in two ways:
1) Continuous: - Start the experiment and watch it happen; you can use a computer “logging” system to monitor it. I.e. watching a colour fade or increase.
2) Discontinuous: - Do the experiments and take readings/ samples from the experiment at different times, then analyse the readings/samples to see how many reactants and products are used up/produced.
We can measure the rate of a reaction by following a simple formula:
Calculation:
raten = Weightn/(elapsed time)
Though as simple way of writing it is:
Rate of Reaction = amount of reactant used up/time taken
If the amount used up is the same each time then the only thing that changes is the time taken so, reaction rate µ 1-time taken.
Rate = K/time taken.
Where K is the constant for the reaction.
Now to find out the rate of the reaction in this experiment, I will follow the formula and use my results to find out what the rate is. I will show this by using a table below:
This is what my results look like when I plot them on a graph
Evaluation
After conducting this experiment I think the investigation went well and I found it was a simple and straightforward procedure to carry out. I believe that my results were of a particularly accurate standard, and I had no difficulties in following the method or using the equipment.
Due to conducting the experiment three times, I find that this helped me produce more precise and reliable results, and when I found the average results and plotted them on a graph it clearly proved to show accurate results. Also, when the results for the rate of a reaction were plotted on a graph, they show a positive correlation, and tend to prove the accuracy, that there were no anomalies, and the rate flows in correlation.
In my experiment, there were no anomalies within my results and I think this was due to extreme caution and care that I put into making sure that the experiment was set up correctly, with careful and accurate measuring of chemicals and substances. Consequently I had no problems in my investigation.
To show how accurate my results are I will plot all my results from the three attempts of my experiment, on one graph and draw a line of best fit. This will enable me to see how precise the results are. Also it will prove whether there is a trend or not.
From the results produced, I can see that when all the results are plotted, they are all fairly close to my line of best fit, tending to prove the accuracy of my investigation. Also, the graph shows correlation further proving the precision and how exact my results are as the points are quite close together.
To make my results more meticulous, I think I could have repeated the experiment a few more times. However, I feel that although, the experiment was repeated three times, the most accurate results in an experiment can only come from constant repeatability, which I did not display in my experiment.
The time allocated did not allow me to do so and I believe as an improvement of what I could do, if I did the experiment again, I would have to say that, with more time I would repeat the results further for even more accurate and reliable results.
I believe I could have improved the method, by making it more specific. I stated all the methods took in setting the experiment up, but I could have been more specific to how all the apparatus was used, and perhaps why I used the equipment I did. I believe that I did get a suitable range of results for this experiment. I recorded results from the temperatures that ranged from room temperature to 65 ºC, which I thought was a fairly reasonable range to see how temperature affects the rate of a reaction. However, I feel this also reduces the limit and chances of knowing if anything changes, if the temperature reaches a certain point. Perhaps measuring the temperature even higher would enhance my results but could become dangerous, so I could not really say I could improve the range of my results to high.
Other areas I feel I could improve on, were factors like controlling the stopwatch and measuring the amount of sodium thiosulphate and hydrochloric acid, there is a lot of room for human error. However, the inaccuracies due to them were negligible because I have paid close attention to these during the experiment. Overall I believe the experiment has a successful one. I feel my results and analysis have been as accurate and reliable as they could have been, under the time allocated. Nevertheless, I feel with extra time, I could have repeated the experiment and made it further accurate and adapted it to other variables, i.e. concentration or adding a catalyst. These are ways I could expand to the original experiment.
The particle theory says that for a chemical reaction to occur there must be a collision at a certain speed and certain angle. Also the factors that affect the rate of reaction are the surface area of the solid reactant, the concentration of the reactant, the presence of a catalyst, the amount of pressure exerted on it and it’s temperature. In this experiment, temperature was my focus, and I able to draw a conclusion that temperature does in fact, affect the rate of a reaction, in that when the temperature is higher the reaction takes less time.
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. I could use a device to help me in my investigation to measure the rate of a reaction. The apparatus I would use is a piece of 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, light intensity, on/off, open/closed, voltage, pressure and events) over time. The data logger is connected to a personal computer. Then a turnkey software is used to select logging parameters (sampling intervals, start time, etc.) and initiate the logger.
The logger records each measurement and stores it in memory along with the time and date. The logger is then reconnected to a personal computer and the software is used again to readout the data and see the measurements as a graph, showing the profile over time. Data loggers incorporate 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.
A remote data logger
