Measure 5cm3 of HCL using a measuring cylinder. Measure 50cm3 of 0.03moles/dm3 concentration of THIO also with a measuring cylinder.
Using a Bunsen burner (plus tripod, gauze, heatproof mat) prepare a ‘water bath’. Basically heat water in a heatproof beaker until it reaches the temperature you want to investigate, remembering to measure with a suitable thermometer.
Once the water bath is at the desired temperature simply place a flask with the 50cm3 of THIO into the water bath carefully.
Leave the flask of THIO in the bath until that too has reached the desired temperature (20-70 0C).
Remove the flask from the water bath and place over a paper with a black cross (which is visible through the solution). (The purpose of the cross is as an indicator to when this particular reaction is complete. When the HCL and THIO are mixed they will form a cloudy precipitate, however, the reaction is only complete once the cross is no longer visible through the flask of cloudy solution.)
Add the 5cm3 of HCL to the flask of THIO. Also start the stopwatch immediately. Stir a little initially.
Record the time taken for the reaction to complete. The beginning of this reaction is immediately as the HCL and THIO are added up until the precipitate formed blocks the image of the ‘black cross’ on the paper. Record the time taken for the reaction to block out the black cross.
Repeat this for each of the temperatures being investigated. Do this twice as to make it a fair test and to identify any anomalies.
Safety
Throughout this experiment, I made sure that safety was one of my top priorities. I wore goggles at all times to protect my eyes. I used a heatproof mat and tripod when using the Bunsen burner and took extreme caution when turning it on and off. I took the same extreme caution when I repeated the results. Here are a few further basic things to remember to carry out a safe experiment;
· Wear safety goggles so nothing can affect the eye which is sensitive.
· Tuck stools in to make sure no one falls in the lab.
· Put all bags outside to make sure no-one falls
· Never run in the lab
· Always stand up when carrying out experiments so we can move away if we are in any danger
Fair Test
To make my experiment a fair one, I had to look at a lot of things. Firstly, I looked at the factors that may have affected how well the investigation would work and these were things like using different equipment or doing the actual experiment in different conditions i.e. a colder/hotter environment. To combat this, I made sure that upon repeating the experiment, I used the exact same equipment and done it in the exact same environment to make absolutely sure that the experiment was fair at each temperature.
I think that these were both very important factors because they could affect the results severely and leave me with an anomalous when I should only have correlating results. To ensure fair and accurate results, all of the factors that can affect my results need to be controlled. I have already mentioned how to control such factors as light, mixing and catalysts.
Whilst doing the experiment you will find that it is extremely difficult to ensure the Thiosulphate is exactly at the desired temperature- this may affect the results so I have noted down the exact temperatures used during the experiment.
Remembering to repeat the experiment is a major factor in trying to ensure a fair test so anomalous results are identified. If there is an error in the 1st time the repeat should hopefully show this up.
Prediction
As I explained earlier, the rate of a chemical reaction is the speed at which it takes place. Temperature is a major factor in this as increasing or decreasing the temperature changes the movement of particles in a substance therefore changing the rate of reaction. When a reaction mixture is heated up, each particle in it acquires more energy and collides more with other particles.
Thus, from my prior knowledge and research, I can make the prediction that if you increase the 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 where these collisions contain enough energy to break the energy barrier, so:
Temperature Raised
Particles, when moving faster, collide with greater power (as they have more energy)
The reaction therefore becomes faster
The collisions between particles break the energy barrier quicker and therefore the RATE OF REACTION increases
On my preliminary results I found the following;
From approximately; 20 to 30oC the rate was increased by 0.004
30 to 40oC the rate was increased by 0.010
40 to 50oC the rate was increased by 0.009
50 to 60oC the rate was increased by 0.016.
However there is no clear pattern so I am unable to make a quantitative prediction. The preliminary graph also shows that there is no direct linear relationship between temperature and rate.
Results
After working out the average Rate we can now plot a graph to show the results
Analysis of Results
From my results, I notice that there is a considerable difference in the time for the cross to disappear from the lower temperatures to the higher temperatures. All of the times are pretty much the same for the two recordings indicating that the experiment was a pretty successful one. There were no anomaly. The average time taken for the reaction descends, as the temperature gets higher- There is a decrease of almost 163 seconds from the starting temperature to the finishing one.
The results clearly show that the time for the cross to disappear decreases as the temperature increases.
In my experiment I found that during the reaction between Hydrochloric acid and Sodium Thiosulphate, when the Hydrochloric acid is added to sodium Thiosulphate solution, a fine deposit of sulphur is formed. The sulphur makes the solution cloudy. As more and more sulphur is formed, the solution becomes more and more cloudy. Soon it becomes impossible to see through the solution.
From my results, I have come to the conclusion that if the temperature of a solution is raised, so is the time for the reaction to occur. The cross disappeared more rapidly as the temperature rose and I think this was due to the increase of energy between the particles and an increase in energy between collisions that successfully passed the energy barrier. This produced the sulphur at an increased rate, which turned the solution cloudy thus making the cross invisible.
At the lower temperatures, the time for the cross to disappear was greater because the particles did not have as much energy as they did at the higher temperatures. At high temperatures the particles are colliding with much more energy and thus the reaction that releases sulphur works and now releases more sulphur at a much quicker rate thus increasing the rate at which the cross disappears.
From the graph it can be seen that at the highest temperatures there is a greater increase in rate. So from;
20-30oC rate increase 0.008s-1
30-20oC rate increase 0.007 s-1
40-50oC rate increase 0.006 s-1
50-60oC rate increase 0.030 s-1
60-70oC rate increase 0.032 s-1
The first three have an average difference of 0.007 s-1 yet the last two have an average difference of 0.030 s-1.
My original prediction was that if you increase the temperature of a reaction, you decrease the time it takes to occur. And, from looking back on my results, I can see that this hypothesis was correct as the time for the cross to disappear decreased as the temperature rose. My conclusion matches my prediction very well overall, and my results clearly show this where at room temperature, the time for the cross to disappear was 274 seconds and at 70oC the time for the cross to disappear was 11 seconds - a difference of about 263 seconds. Thus when Hydrochloric acid was reacted with Sodium Thiosulphate the particles in the solution were moving around with more energy; enough to break the energy barrier and for a reaction to occur as the temperature rose.
Evaluation
I think that this experiment has gone very well. My results were of a particularly accurate standard as I did each temperature the reaction was taking place twice and calculated an average from these times. There were no strange results (anomalies) within my results table although I didn’t get the exact results I expected. I found that during the last two temperatures the rate was much increased.
Reliability of results can only be shown by repeating the experiment a number of times. I could have therefore improved upon the reliability of my experiment by repeating the experiment 10 times. The reason this was not done initially was due to time considerations that are imposed in a classroom situation.
Accuracy of my results was dependant upon my observations so I may have introduced an error into the results. This is because my judgement of the cross disappearing may differ to another students, so were they to repeat my practical they may not obtain results which tally with mine. This however does not effect the overall analysis of my practical as I alone judged when the cross had disappeared therefore negating the error. In order to obtain results which are of a more accurate nature I could have used a light meter to judge the intentsity of the precipitate formed.
I believe that I did get a suitable range of results for this experiment. I recorded results from temperatures that ranged from Room Temperature to 70oC and I think that this is a very good range to see how temperature affects the rate of reaction. However, I feel that this also reduces the chance of knowing if anything changes if the temperature reaches a certain point. Perhaps raising the temperature even higher would have produced a different set of results which may mean that a limit may exist for the rate of the reaction.
Some other areas in the experiment that I feel I could have improved on were factors like controlling the stopwatch and measuring the amount of Sodium Thiosulphate and hydrochloric acid. There is lots of room for human error here. For example I could have used a burette for measuring the HCL or Thiosulphate rather than using a measuring cylinder. However the inaccuracies due to them were negligible because I paid close attention to these during the experiment. I did outline in my plan that I was going to heat the Sodium Thiosulphate using a water bath, however, this option was not available to me due to the lack of time and resources, I ended up heating the Thiosulphate in a flask sitting on a gauze mat.
This first part of the investigation has been a very successful one. I feel my results and analysis have been as accurate and reliable as they could have been under the time allocated.
NB. Further work is suggested at the end of the overall experiment
Part 2: concentration
Concentration
In this certain investigation I will be seeing how varying the concentration of Sodium Thiosulphate affects the rate of reaction when mixing it with Hydrochloric acid. The rate of reaction will vary as we vary the concentration of THIO. Increasing the concentration of a chemical means that the particles of the chemical will be increased per set area. Concentration affects rate as the higher the concentration (of particles) the higher chance there is of them colliding with HCL particles (and breaking bonds), as there is more chance of the particles colliding this would mean that the particles would collide quicker this would result in the reaction being completed quicker.
Preliminary Results
I conducted a preliminary experiment where I added HCL to different concentrations of THIO (0.03, 0.06, 0.09, 0.12 & 0.15 moles/dm3). Here are the results I found
From these results we can make a preliminary graph.
The Experiment
APPARATUS
Hydrochloric acid (2 moles/dm3)
Sodium Thiosulphate (0.03, 0.06, 0.09, 0.12 & 0.15 moles/dm3).
Conical flask
Measuring Cylinder
Stopwatch
Safety Mat
Diagram
HERE THE THIO (0.03 MOLES/DM3) AND HCL ARE REACTING AND THE TIME TAKEN FOR THE PERCIPITATE TO FORM OR THE ‘X’ TO DISAPPEAR IS BEING COUNTED ON THE STOPWATCH
Method
First prepare the reactants. Measure (with a measuring cylinder) 50cm3 of THIO at 5 different concentrations 0.03, 0.06, 0.09, 0.12 & 0.15 moles/dm3 and 5cm3 of HCL acid at 2 moles/dm3. Make sure there is 25cm3 of HCL acid, as it will be reacted with each of the 5 different concentrations of THIO using 5cm3 each time.
Prepare a piece of paper with a clear black cross about the size of the base of a conical flask. Make sure all safety precautions are setup- safety goggles and safety mat etc.
In a conical flask add 5cm3 of 2 moles/dm3 of HCL acid along with 50 cm3 of THIO at one of the 5 different concentrations (0.03, 0.06, 0.09, 0.12 & 0.15 moles/dm3), which is being investigated. Also start the stopwatch immediately. Stir a little initially.
Record the time taken for the reaction to complete. The beginning of this reaction is immediately as the HCL and THIO are added up until the precipitate formed blocks the image of the ‘black cross’ on the paper. Record the time taken for the reaction to block out the black cross.
Repeat this for each of the concentrations of THIO being investigated. Do this twice as to make it a fair test and to identify any anomalies.
Safety - refer to page 7 in ‘part 1: temperature’ to see classroom and experiment safety.
Fair Test
To make my experiment a fair one, I had to look at a lot of things. Firstly, I looked at the factors that may have affected how well the investigation would work and these were things like using different equipment or doing the actual experiment in different conditions i.e. a colder/hotter environment. To combat this, I made sure that upon repeating the experiment, I used the exact same equipment and done it in the exact same environment to make absolutely sure that the experiment was fair at each concentration.
I think that these were both very important factors because they could affect the results severely and leave me with an anomalous when I should only have correlating results. To ensure fair and accurate results, all of the factors that can affect my results need to be controlled. I have already mentioned how to control such factors as light, mixing and catalysts.
Prediction
I predict that the higher the concentration the faster the reaction will take place this is because in a higher concentration there will more Sodium Thiosulphate molecules per set volume. This means that there will be a higher chance of the Sodium Thiosulphate molecules colliding with the Hydrochloric acid molecules and reacting. This should in theory increase the rate of reaction as the concentration is increased.
Concentration increased
More particles in same size space means more chance of collisions
More collisions mean reaction is completed quicker
Rate of Reaction is increased
The increase in the concentration should be directly proportional to the increase of the reaction rate at a given time. This is because by doubling the number of Sodium Thiosulphate acid molecules present the chance of a collision should be doubled, as there is now twice the possibility of a collision-taking place initially. This can be thought of as like people in a refined space, if there are twice the number of people there will be twice the chance of people colliding.
0.03 moles/dm3 of THIO and HCL 0.06 moles/dm3 of THIO and HCL
Using a numerical prediction I found from the preliminary results that each time the concentration of THIO was raised by 0.03 moles/dm3 the rate of reaction increased at an average of 0.008 s-1. so I predict that each time the concentration of THIO is raised by 0.003moles/dm3 the rate of reaction will increase by 0.008 s-1.
Results
After finding the average rate I can now plot a graph to show this.
Analysis of Results
From my results, I notice that there is a considerable difference in the time for the cross to disappear from the lower concentrations to the higher concentrations of THIO. All of the times are pretty much the same for the two recordings indicating that the experiment was a pretty successful one. There is no anomalousness and the average time taken for the reaction descends, as the concentration increases at a positive correlation as I predicted. There is a decrease of almost 242 seconds from the starting concentration (0.03moles/dm3) to the finishing one (0.15moles/dm3).
The results clearly shows that the time for the cross to disappear decreases as the concentration increases resulting in an increase of the rate of reaction.
In my experiment I found that during the reaction between Hydrochloric acid and Sodium Thiosulphate, When the dilute hydrochloric acid is added to Sodium Thiosulphate solution, a fine deposit of sulphur is formed. The sulphur makes the solution cloudy. As more and more sulphur is formed, the solution becomes more and more cloudy. Soon it becomes impossible to see through the solution.
From my results, I have come to the conclusion that if the concentration of a solution is raised, so is the time for the reaction to occur. The cross disappeared more rapidly as the concentration was increased and I think this was due to the increase of successful collisions that passed the energy barrier. This produced the sulphur at an increased rate, which turned the solution cloudy thus making the cross invisible quicker- indicating an increase in the rate of reaction.
At the lower concentrations of THIO, the time for the cross to disappear was greater because the particles did not create as many successful collisions fast enough to pass the energy barrier quickle. At high temperatures the particles are colliding with much more succes and thus the reaction that releases sulphur works and now releases more sulphur at a much quicker rate thus increasing the rate at which the cross disappears.
In my ‘quantatative prediction’ I predicted that the rate would increase by 0.008 s-1 as the concentration increased by 0.03moles/dm3. This was very accurate as the rate actually increased at 0.007 s-1
My original prediction was that if you increase the concentration of a reactant, you decrease the time it takes to occur. And, from looking back on my results, I can see that this hypothesis was correct as the time for the cross to disappear decreased as the concentration rose. My conclusion matches my prediction very well overall, and my results clearly show this where at 0.03moles/dm3 took 275 seconds, the time for the cross to disappear (and complete the reaction) was 33 seconds at 0.15moles/dm3 the - a difference of about 242 seconds. Thus as the number of particles of THIO was greater there was a greater chance of successful collisions to break the energy barrier and release the sulphur for the reaction to complete. At higher concentrations this happened quicker so the rate of reaction therefore increased.
Evaluation
This experiment has gone very well. My results were of a particularly accurate standard as I did each concentration the reaction was taking place twice and calculated an average from these times. There were no strange results (anomalies) within my results table and I think that this was because of the extreme caution and care that I put into making sure that the experiment was set up correctly with careful measuring of chemicals.
Reliability of results can only be shown by repeating the experiment a number of times. I could have therefore improved upon the reliability of my experiment by repeating the experiment 10 times. The reason this was not done initially was due to time considerations that are imposed in a classroom situation.
Accuracy of my results was dependant upon my observations so I may have introduced an error into the results. This is because my judgement of the cross disappearing may differ to another students, so were they to repeat my practical they may not obtain results which tally with mine. This however does not effect the overall analysis of my practical as I alone judged when the cross had disappeared therefore negating the error. In order to obtain results which are of a more accurate nature I could have used a light meter to judge the intensity of the precipitate formed.
I believe that I did get a suitable range of results for this experiment. I recorded results from concentrations that ranged from 0.03moles/dm3 to 0.15moles/dm3 and I think that this is quite a good range to see how concentration affects the rate of reaction.
Some areas in the experiment that I feel I could have improved on were factors like controlling the stopwatch and measuring the amount of sodium Thiosulphate and hydrochloric acid. There is lots of room for human error here. For example I could have used a burette for measuring the HCL or Thiosulphate rather than using a measuring cylinder. However the inaccuracies due to them were negligible because I paid close attention to these during the experiment.
In a final conclusion this investigation has been a very successful one. I feel my results and analysis have been as accurate and reliable as they could have been under the time allocated. However I feel with extra time, I could have repeated the experiment and made it even more accurate and adapted it to try other variables i.e. adding a catalyst. These are the ways that I could expand on the original question. Further work I could attempt is to see if the rate of reaction increases similarly for other reactions, e.g. hydrochloric acid and magnesium ribbon, when the temperature of the reactants is increased or deduce if there is a unique increase in the rate of the reaction for individual reactions with temperature variation.
I could also see if my quantitative prediction for concentration also held true with other reactants such as Magnesium and Hydrochloric acid etc.
Bibliography
(includes direct quotes)
Letts’ Science study guide
Letts’ Chemistry (Higher)
