Pressure – The higher the pressure, the more collisions occur and so the rate of reaction is greater. This is because the particles are squashed together which results in them colliding more often. I didn’t do this test as this does not apply to my investigation, because in my experiment the reactants are liquid and solid (sulphur) and both of these substances are difficult to compress, unlike gases.
Preliminary test:
By doing a preliminary test I want to find out how I should put the substances in the conical flask and I also need to find out how I should measure my time, so that I could keep it a fair test.
I have found out that the best way to do the experiment is to get a large amount of all the substances that are being used in the experiment so that I do not need to keep going to refill the beakers, I cannot use a measuring cylinder that measures up to 10cm³ substances because it will not be enough, a 50cm³ measuring cylinder will be most appropriate. I have decided to use two measuring cylinders so that when I measure out the substances I do not need to wash them out, if I used the same one for measuring sodium thiosulphate and HCL then they could it could be harmful. I now know that when I do the experiment I am going to keep the total volume at 40cm3. Also, I have found that it is easier and clearer to use a thick outlined cross on a piece of paper rather than under the beaker to indicate when the solution is opaque.
By doing this preliminary test I was able to decide my final plan pr procedure. I did know how to do the experiment but it wasn’t perfect and this pilot (preliminary test) enabled me to fix the experiment and make it better as well as safer.
I haven’t recorded the result and presented it because this was not the real test.
Apparatus:
Here I have listed the equipment I used in the experiment and what they are for:
Goggles: These are sort of protective eye wear, and a used in laboratories in order to stop chemicals shooting or entering the eye as this may cause irritation and can be harmful.
Heatproof mat: This is a mat that is placed under the tripod. As the tripod is made from metal
Teat pipette: For accurate measurement using this can be used. It is also convenient because rather than pouring the sodium thiosulphate or HCL out into the measuring cylinder and this can sometimes drop. Therefore it can also prevent spilling.
Thermometer: This contains mercury and measure the temperature of its surroundings.
Stop watch: This is used to measure the time of the reaction.
Square piece of paper: I will use a white piece of paper, with a black cross, the paper is not really required to be square, and however it should be a sensible size. A3 is what I will use.
250 cm3 conical flask: This is where the experiment is held, it holds substances.
Measuring cylinder(x2): Used to measure out liquids, 2 are essential as there are 2 chemicals
Sodium thiosulphate: My investigation is based upon 2 chemicals and this is one of them, this is the liquid that is going to be boiled in order to do the temperature test.
Hydrochloric acid: This is the chemical that is to be added to the sodium thiosulphate and in the concentration test – the concentration of HCL is to be increased.
Tripod: A three-legged supporting stand, underneath this the Bunsen burner is placed.
Bunsen burner (and a rubber tube/pipe): A Bunsen burner is a gas burner which is used for heating, sterilization, and many other uses.
Gauze: This is a mat that is place upon the tripod for placing an object on. In this test it is going to be holding a conical flask.
Tongs: These are for convenience because when the conical flask is heated it gets hot, and can burn a naked hand; this can be used to pick it up
Gloves: These are not really needed, however can result in saving the investigator from damage to themselves. There are chances for when the acid could be spilt and end up on my hand that’s why I will wear these to enhance protection.
Method:
Concentration:
Prepare the following solutions:
∙ Hydrochloric acid
∙ Sodium thiosulphate
Rinse, clean and set up the apparatus.
Use a measuring cylinder to measure the same volume of acid each time. Suggest use 20ml.
Take at least three different concentrations of acid
Measure out 20ml of sodium thiosulphate into a beaker or conical flask.
Place a mark on the reaction vessel or on a piece of paper, I marked a black cross on white paper and using black is good because the solution goes cloudy (can be described as white). This then creates a good colour difference between the solutions and cross therefore can help get accurate results.
Use the same flask each time and wash it out carefully with distilled water.
You must use the same depth of reaction mixture each time to make it a fair test.
Add the acid to the sodium thiosulphate in the flask and start the clock straight away.
Look at the cross on the paper through the reaction mixture and measure the time it takes to disappear.
Repeat with the same concentration of acid to make sure you get a similar time. Now you can change the concentration of the acid.
You need to use different concentrations.
Now add this to 20ml of fresh sodium thiosulphate and repeat as before.
Use pipettes and /or burettes to put the following solutions into a suitable reaction vessel (conical flask).
Do not add the acid until you are ready to record the time for the reaction to start.
Time how long it takes for the mark on the paper to disappears (vanish).
This experiment should be repeated with different concentrations of the liquids (more molecules per cm3).
Temperature:
Prepare the following solutions:
∙ Hydrochloric acid
∙ Sodium thiosulphate
Rinse, clean and set up the apparatus.
Measure out 20 cm of both of the solutions; this can be increased depending on the investigator will. However as this test is about temperature it is absolutely essential that the amount of both of the solutions is identical as this will make it a fair test, which is essential for reliable and accurate results.
Pour the sodium thiosulphate into a clean conical flask. Leave the HCL in the measuring cylinder, however make sure that you don’t drop it hence put it in a safe place.
Get the heat proof mat – then place it on the work place.
After this is I shall get the tripod and place in on top of the heat proof mat.
Then collect the gauze and place that upon the tripod.
Put the Bunsen burner beneath the tripod.
There is a rotatable part close to the bottom of the Bunsen which should be turned so that the air hole. This would make the flame on safety form.
A rubber pipe should be attached to the source that provides the gas, and to the Bunsen burner.
The gas should only be turned on once the Bunsen is ready to light.
Place the match or a stick with a little flame (or any source that provides a flame), on top of the Bunsen and then it will catch fire.
Then get the conical flask with sodium thiosulphate, place a thermometer inside it.
Use the tongs or you hand to place the conical flask on top of the gauze that is placed on the tripod.
Now as I am heating the liquid, to speed thing up, I will rotate the part on the bottom of the Bunsen so that the air hole is closed.
This should be stopped when the temperature is 20⁰, as this is the lowest one I will test.
Use the tongs to get the conical flask off the Bunsen.
Place the flask on the piece of paper with the black cross.
Pour the hydrochloric acid into the reaction vessel (the one with sodium thiosulphate).
Start the stopwatch as soon as the hydrochloric acid is in the flask.
Time how long it take for the cross to disappear.
Repeat this experiment with different temperatures.
Diagram:
Fair test:
In order to make this experiment a fair test and reducing the amount of errors I made I will have to:
Take the water from the same source (i.e. same tap)
Take hydrochloric acid and sodium thiosulphate from the same source.
If you stir once then do it all through the experiment.
Repeat each experiment two times to get an average time.
Keep the method the same all the way through, so that each reaction is at the same stage.
Wash out conical flask after use each time
Dry conical flask after it has been washed.
Use the same measuring cylinders with clear, even and frequent measurements marked on them.
Put the hydrochloric acid in the same way, as well as the same amount
Start the timer as soon as hydrochloric acid entered the sodium thiosulphate.
Using the same stopwatch, as some different stop watches have different properties and accuracy levels.
Use separate containers and measurers so the substances do not get mixed up.
There are many variables that affect the results; the factors that are most likely to cause inaccuracies are going to be the temperature in the room that I cannot control, this does not matter in the temperature experiment however may create difference when testing concentration only. If I measure the sodium thiosulphate, hydrochloric acid in the same way and with the same equipment then the results are likely to be more accurate. The substances which effect and the hydrochloric acid or sodium thiosulphate can cause inaccuracies (water from washing out the flask).I can control this by washing the conical flask after use, and also drying it thoroughly. I also have to use the same amount of hydrochloric acid each time. To make the measuring easier I have used a pipette, but I have also used a measuring cylinder, so that I can put small drops of a substance to make it accurate.
Safety:
For this experiment:
You will need to wear eye protection-GOGGLES. You will be handling acid.
You will need to be aware of your surroundings- NO RUNNING. You will be handling chemicals such as hydrochloric acid. Spillages, breakages, of any kind are a danger hazard. Keeps your experiment away from any students’ experiments investigating temperature as their variable as they may be using Bunsen burners. Hydrogen is flammable and it would be dangerous for it to be set alight.
You will need to rid your hands of any traces of chemicals such as acid after carrying out your experiment- WASH YOUR HANDS. You will be handling acid, a clear, water like substance (to the eye), if you have any traces of acid on your hands and then put your hands in your mouth or on any food substance and the eat it you could make yourself ill.
You will need to handle the acid- ACID, HANDLE WITH CARE. Any wrong move could cause an accident.
You will need to take off any lose, baggy accessories that may become an obstruction- TAKE OFF ACCESSORIES. You jewellery etc. could be an obstruction and/or could be damaged.
You will need to roll up your sleeves- ROLL UP SLEEVES. Your sleeves could be an obstruction and/or could be damaged.
You should not boil the acid.
You should not boil sodium thiosulphate above 80⁰, as this will cause the liquid to boil energetically and hence it would spill.
You must make sure that coats and bags are all out of the way while doing the experiment. Ties and hair should be tucked out of the way, so they do not make contact with any of the chemicals. It would also be preferable to wear a scientific apron, however this is not
essential.
You should not eat or drink in the lab while doing these experiments.
Results:
Graphs:
Conclusion:
Graph 1: - Temperature
For temperature I predicted:
“If I double the speed at which doubling at which the particles travel will double the rate of reaction as they can travel faster so it double the probability of them colliding.”
To a certain extent this was right, I basically predict that: The higher the temperature, the faster the reaction.
This was exactly what happed, how the effect of doubling the temperature was greater than just doubling the rate. For example when the temperature was 20⁰ the rate was 0.18. The double of 20⁰ is 40⁰ and the rate at this temperature was 0.61, therefore:
0.61/0.18 = 3.89. So the rate was nearly 4 times as much.
By looking at the graph I also can prove that the temperature has a great effect on the rate because the line on the graph has a negative correlation. This means that as the temperature increases the rate decreases.
This can be explained through the collision theory. Here is what the theory claims:
The collision theory says that the more collisions in a system, the more likely combinations of molecules will happen. If there are a higher number of collisions in a system, more combinations of molecules will occur. The reaction will go faster, and the rate of that reaction will be higher.
Reactions happen, no matter what. Chemicals are always combining or breaking down. The reactions happen over and over but not always at the same speed. A few things affect the overall speed of the reaction and the number of collisions that can occur.
When the temperature is higher, then the particles of sodium thiosulphate are moving at a greater speed than normal. Therefore when the hydrochloric acid enters the sodium thiosulphate, its temperature also increases. This cause makes the particles of both solutions moving faster than usual, and as they are moving faster they collide very often, which then makes them react. However only colliding doesn’t make them react, the particles need sufficient energy, which is known as the activation energy. This is not the problem in temperature because as they are hot they are moving very fast which cause them to have a greater chance to react.
Graph 2: - Concentration
For concentration I predicted that:
The number of particles doubles the probability that they will collide. Therefore they will react quicker, and the rate or reaction will increase.
The prediction was a precise one; however I said that the rate would double if the concentration the rate of the reaction didn’t double, the effect was greater. To demonstrate this; if I see the table, when the concentration is 15(g/dm3) the reaction time is 0.1 however if I double the concentration then it would be 30 (M), the rate is 0.53.
0.53/0.1 = 5.3, however if I follow my prediction then I should obtain the result 2, but this augmented the rate by just about 5 times.
If I observe the graph, I see that the line is going down therefore when the concentration increases the time decreases. The line also has a negative or indirect gradient so as the concentration increases and the time decreases. This is similar to what I predicted.
These results can be explained by the particle theory. The particle theory says:
The particle theory explains heat and temperature and the difference between, say, 20ºC and 50ºC. The particle theory is based on a model that suggests that all matter is made up of tiny particles too small to be seen. According to this model, these particles are always moving - they have energy. The more energy they have, the faster they move. So far, all the evidence is made up of moving particles. That is why we call the particle model for matter a theory.
The particle theory is a useful model to explain why substances expand when they are heated and contract when they are cooled. At high temperatures, particles have more energy, move more quickly, and have more collisions. As a result, they take up more space, and the substance expands. At lower temperatures, particles have less energy, move more slowly, and have fewer collisions. They take up less space, and the substance contracts.
Increasing the concentration of something means having more particles in a certain amount of space. Moreover, as the result of the number of particles increase the space gets squashed so there is a higher chance that they will collide and react. Therefore, when the 2 liquids are poured into the reaction vessel there are more particles so reaction is faster
Although I predicted that concentration would have the greatest affect on the reaction rate, it was in fact temperature. This was mainly because the concentration was tested at room temperature which wasn't enough to get many of the particles to activation energy levels. In addition, in the solution there were plenty of particles so concentration wasn't important.
Evaluation:
The investigation could have been improved by testing the temperature variable on the computer as the. It would also have helped to test each concentration and temperature more than once to ensure that the results were true. I could also have used a burette to measure out the reactants although the measuring cylinder was quite accurate.
I think I could have improved my investigation by:
· Obtaining more results to get a better overall result.
· I used ICT to display my coursework, but I did not use it in any way that affected the experiment.
· I would like to do a further experiment to confirm my results. However I am restricted by time and the available facilities which means I cannot repeat it.
· Also instead of using a cross on a piece of paper I could use a single beam of light until it could no longer be seen
· Use of computer to aid analysis of results
Candidate Name: Farhan Khalid 9Sc5
Centre Name: Wembley High Technology College
Centre no: 12346
Teacher: Mr Bullock
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