Another factor that affects rate of reaction is light. Light gives the reacting molecules more energy to move around. So sunlight or a good light source is needed to speed up the rate of reaction.
Another factor that affects the rate of a reaction is the surface area. The surface area of a solid is the amount of surface area on the outside. The larger the surface area the quicker the rate of reaction.
The last main factor that affects the rate of reaction is catalysts. A catalyst works by providing a substitute reaction path that has lower activation energy. Catalysts are used to speed up reactions, for example, if a tube of hydrogen is exposed to the air, nothing happens but if a piece of platinum wool is placed at the mouth of the tube the hydrogen burns with a squeak. So to speed up the rate of reaction, a catalyst should be used.
For a chemical reaction to occur, the reacting particles must bang or collide into each other with enough force or energy to break bonds. This is called the collision theory. If particles do not have enough energy, they will harmlessly bounce off one another. If the particles meet, they may rebound without a reaction. But if they collide with enough force, a chemical reaction will occur. The diagram below shows that the top diagram has got enough energy to react and form a reaction. Whereas, the bottom diagram has not got enough energy to react with one another so the two particles jus harmlessly glide past each other.
Formulas:
The formula for sodium Thiosulphate is:
Na S O
The formula for sodium thiosulphate and hydrochloric acid put together is:
Na S O + 2HCl → 2NaCl + S + SO
The rate of reaction is measured by dividing 1 by the time taken for the reaction to take place.
(1 ÷ time).
Prediction:
I predict that the higher the concentration of sodium thiosulphate mixed with hydrochloric acid will have a faster rate of reaction, instead of a weaker concentration of sodium thiosulphate that will have a slow rate of reaction. The double the concentration of sodium thiosulphate then, the double the rate of reaction. So the 40ml of sodium thiosulphate reacting with 10ml of water will be faster than, 10ml of sodium thiosulphate reacting with 40ml of water.
The higher the temperature of the sodium thiosulphate then the faster the rate of reaction. This is due to the fact that the particles that have more energy move faster. So they will collide more often with more energy. Particles with more energy are more likely to overcome the energy barrier to the reaction so they will react successfully. Collisions between particles are therefore likely to occur.
This means that the graphs in the analysis will have a positive correlation and will probably be curved as the increase in the rate of reaction will not be exactly the same as the concentration.
Equipment List:
The apparatus that I am going to use to conduct the experiment are as follows:
- Sodium Thiosulphate.
- Hydrochloric acid.
- Black marker pen.
- Plain paper.
- 10ml measuring beaker.
- 50ml measuring beaker.
- 200ml conical flask.
- Stopwatch.
- Distilled water.
- Thermometer.
Safety Aspects:
The experiment must be carried out in a safe way. The safety aspects that I am going to consider to make my experiment are as follows:
- All long hair must be tied back so that it does not get caught on anything or so that it is not in the way of carrying out the experiment..
- All loose clothing such as ties should be kept secure by lab coats so that it is not in the way or so that the does not get caught on anything.
- When pouring the sodium thiosulphate into the measuring beaker it must not spill anywhere on the workbench or on anyone.
- The hydrochloric acid should not be spilled on anyone and should be washed off immediately with water if it comes into contact with anyone. So it must be kept away from the edge of the table to ensure that it does not fall off of the edge.
- The acid must be kept away from the edge of the table so that it does not drop and spill on the floor.
- When we do this experiment, it may be necessary to wear safety goggles, as things are very unpredictable, and even though it is very unlikely that the solution would come out of the conical flask during the experiment, one must still be cautious of spills.
Variables:
The variables for this experiment are as follows:
- The independent variables are the concentration of the sodium thiosulphate and the amount water.
- The dependant variable is the rate of reaction.
- The control variables are the volume of the sodium thiosulphate, volume of the hydrochloric acid, the standardised volumes of the flasks, the measuring beakers, the conical flask and the concentration of the hydrochloric acid.
Fair Test:
To insure that the investigation is carried out in a fair way, some careful planning is involved. The same amount of hydrochloric acid must be used (5 ml), to assure that this happens I must measure it out with the same 10ml measuring cylinder. The same standardised volumes for the flasks must be the same. The size of the measuring cylinders and the conical flask must also be the same.
The things that do not change are the independent variables, (the concentration of the sodium thiosulphate and the amount of water).
Method:
The method that I am going to use to carry out this experiment is:
- Draw a cross using a black marker pen on a piece of paper that is equivalent to the diameter of the conical flask.
- Measure 5ml 2M HCl into 10ml measuring cylinder.
- Pour the 2M HCl into 200ml conical flask.
- Measure out 50ml of sodium thiosulphate into a 50ml measuring cylinder.
- Put the conical flask over the cross.
- Add the 50ml of the sodium thiosulphate to the 2M HCl and time with a stopwatch how long it takes for the cross to disappear form the paper. The reason that it disappears is because they the two solutions react together to form a precipitate of sulphur that obscures the cross.
- Repeat the experiment with the following dilutions of sodium thiosulphate. When using 40ml of sodium thiosulphate, 10ml of water is needed. Then when using 30ml of sodium thiosulphate, 20ml of water is needed. Then when using 20ml of sodium thiosulphate, 30ml of water is needed. Finally when using 10ml of sodium thiosulphate, 40ml of water is needed
- Repeat the experiment 5 times for each concentration of sodium thiosulphate to get reliable results.
- Repeat steps 1-8 five times.
Results:
Here are my tables of results:
This is the first set of results.
This is the second set of results.
This is third set of results.
This is the forth set of results.
Here are the average sets of results:
Here are the results for the rate of reaction:
The graphs on the rate of reaction and the average results are on the next page.
Conclusion:
After the form of a precipitate that covers the cross is formed a yellow substance is formed also a smell came from the yellow substance. This shows that a chemical reaction has occurred. A smell came from the substance because there was a diffusion of gases.
Diffusion of gases is the spreading of a substance due to free random movement particles. Due to the fact that the molecules in a gas are moving so fast, gases will spread and take up as much space as possible. This is the reason why smell travel so quickly because the gas particles are also moving quickly to.
The kinetic theory is the way matter behaves. The theory is that matter is made of particle and that these particles are in constant motion. The particles become much more violent as the temperature increases.
After looking at my results tables and graphs, I have determined that my prediction was right. I predicted that the higher the concentration the less time the rate of reaction occurred. Looking at my graph shows that there are only two anomalies, which were the results at 10ml and 20ml of sodium thiosulphate concentration. If there are not a lot of anomalous results then the results are good and but the anomalous results need to be repeated so that they are do not become anomalous. But this was not so because, I did not time to jus repeat the anomalous results. But all the other three results are close to the line of best fit. The line of best fit is in a curve instead of a straight line.
To make the results accurate, a piece of equipment called a burette could be used. A burette is a tube which is usually made out of glass and has a tap at the end of it with graduation marks along the side. They are used to measure volumes of liquids for example, during titrations. Burettes should be used at the temperature that is marked on their sides when using them with alcohol or organic mixtures. But if I had used a burette to measure out the sodium thiosulphate and the hydrochloric acid concentrations then, they would have been measured properly.
When the temperature is being varied a water bath will be used to heat up the sodium thiosulphate and the hydrochloric acid to the necessary temperature. By doing this then the results would have been accurate and there probably would not have been many anomalies.
In my plan I wrote that I was going to carry out the experiment five times to enable me to get accurate results. But I was only able to carry out the experiment four times as I ran out of the sodium thiosulphate. But I still got quite accurate results and they proved that my prediction was correct.
Evaluation:
Overall, the experiment went as planned and I followed the correct method to get the best results that I could get. But to get better results I should have used a burette to measure out the sodium thiosulphate and hydrochloric acid concentration to get the correct measurement just in case I used less or too much concentration. This could have also altered my results.
Bibliography
The Dorling Kindersley Science Encyclopaedia
A Science Dictionary of GCSE by Ron Joyner
Chemistry Revision Guide
