I predict that as the temperature increases, the speed of the reaction will increase. This is because the particles that have been heated will gain kinetic energy and move faster which increase the speed of the reaction. Therefore there are more chance of collision between reactant molecules and the rate increase. However, before any changes take place on collision, the colliding molecules already have a minimum kinetic energy that is call activation energy. If the temperature increase, this lower down activation energy. I predict that increases in 10 degree temperature will double the rate of reaction.
When gases or liquids are heated the particles gain kinetic energy and move faster (see diagrams below).
The increased speed increases the chance (frequency) of collision between reactant molecules and the rate increases.
However this is NOT the main reason for the increased reaction speed!
Most molecular collisions do not result in chemical change.
Before any change takes place on collision, the colliding molecules must have a minimum kinetic energy called the Activation Energy shown on the energy level diagrams below (sometimes called reaction profile/progress diagrams).
The purple arrow up represents this minimum energy needed to break bonds to initiate the reaction, which is the activation energy.
Going down the other side represents the new bonds formed in the reaction products. The red arrow down represents the energy released - exothermic reaction.
It does not matter whether the reaction is an exothermic or an endothermic in terms of energy change; it’s the activation energy which is important in terms of temperature and reaction speed.
Now heated molecules have a greater average kinetic energy, and so at higher temperatures, a greater proportion of them have the required activation energy to react.
This means there is an increased chance of 'fruitful' higher energy collision that greatly increases the speed of the reaction.
Also I predict that catalyst can speed up the reaction. I believe that because catalyst is a substance that in contact with the reactant, which changes the rat of reaction without itself being chemically changed in the end. It increases the rate of reaction by helping break chemical bonds in reactant molecules. It does not get used up and can be reused with some more reactants. Although it does take part inn the reaction, but it does not increase the energy of the reactant molecules. It is only a substance that can speed up the reaction.
Increasing the pressure can speed up the reaction by reducing the volume in which the same amount of particles exist the pressure is increased. Once the same numbers of particles are in a smaller area there is less space in which to move and so the particles are more likely to hit each other. It is therefore possible to predict that increasing the pressure will result in an increase in the rate of reaction. I will not test this variable because the school doesn't have the facilities to test it. However pressure is a continuous variable
Surface area can also speed up the reaction. Particles can only collide when the two sorts can meet. Therefore a reaction can only occur on the surface of the material. By increasing the area of the material which is available to collide the speed of the reaction will increase. I predict that doubling the surface area wills double the speed of the reaction. This variable is continuous but I shall not test it because it is hard to control the exact surface area of the two reactants as they both come in an aqueous solution.
Safety
Laboratory Safety - Protective clothing
· Students must wear protective glasses or safety goggles when diluting concentrated acids, bases, or heat chemicals. There is always the danger of hot or caustic materials being splashed into the eyes.
· Students should wear strong shoes and take care of unbuttoned long sleeves and long hair.
· Students must wear protective clothing, e.g. gloves, aprons, safety goggles when chemicals are being handled. Teachers should be aware of students who wear contact lenses.
Laboratory Safety - Experimental procedures
· While performing the experiment, students should ensure to set the things in the middle of the table and not at the side because it may fall off.
· Read the label on reagent bottles twice to avoid errors.
· Always follow exactly the instructions for chemical experiments.
· Do not substitute another chemical for chemicals specified in the experiment.
· Clean up the area after use.
· Wash your hands.
Apparatus
- Stopwatch- calculate the time the reaction takes
- Gas syringe- to collect the carbon dioxide
- Ices - to make the temperature lower
- Hot water- to make the temperature increase
- Measuring tube- to measure the amount of acid
- Marble chip- medium
- HCL
- Thermometer- to find out the temperature
- Conical flask-where the reaction occur
- Spoon- to get the marble chip
Method
Once I have set up the apparatus I will measure out 20cm3 of acid in a measuring tube and then pour it into the conical flask. I will quickly place the chips into the acid, insert the bung in the top of the boiling tube and start the stopwatch. This must be done in as short a space of time as possible. From then on, I must take the reading of the volume in the gas syringe after a certain point is reached.
Then recorded the amount of carbon dioxide in the gas syringe. I will accurately record these roughly in a table and write them up neatly later.
Here is my table that I’m going to record the readings.
I will take into consideration that the speed with which I put in the marble chips, place in the bung and press the stop watch may well affect how well the experiment works. Although these factors will affect the end result so long as they are kept constant throughout then it should not matter too much.
To get the best possible results I need to use the equipment in the best possible way, I could twist the gas syringe back and forth so as not to get the syringe stuck, which would affect my results. I will need three readings for each concentration and later if I need to repeat any experiments I can.
An important point is that I must use the right amount of acid and the best sized amount of marbles. I did an experiment beforehand to give an idea as to what to do in our investigation. It was the reaction between marble chips and hydrochloric acid. This was a very good thing to do because it showed me how to use the equipment properly and safely and gave an idea as to what was to come.
Fair Test
To ensure that our results were accurate and reliable my group and I had to take into consideration the following points.
1. The fact that each marble chip had its own surface area, which could have affected our results. To try and over come this problem we used chips that weren't too big, yet weren't too small so that the surface area only differed a little.
2. The hydrochloric acid used was of the same molar solution for all experiments.
3. We repeated the experiments three times and then found the average of our results.
4. The apparatus used was the same for all experiments to ensure that the experiments were fair.
5. The temperature was kept changing within each experiment.
6. And lastly we used a more accurate measuring cylinder, so our results would be reliable.
Each time I repeat the experiment I will keep the surface area of the marble chips, amount of acid used and the amount of carbon dioxide to be collected the same. These are the other factors, which may affect the rate of reaction. The variable that I am going to change is temperature. I change it by adding ices and hot water during the experiment.
Variable that I will keep constant
Surface area of the marble chip because if I use different size of marble chip in each experiment, this will make the experiment unfair.
Concentration of acid- to make the experiment fair.
Variable that I will change
Temperature- to find out the rate of reaction at different temperature.
Conclusion
Before I did the experiments I predicted that the more concentrated the hydrochloric acid was the quicker the carbon dioxide would be produced. This was completely correct because what I thought would happen do.
I also investigated the effects of temperature on the rate of the reaction as I have predicted that temperature may affect my experiment/results. I backed up this prediction using the collision theory, which states that at higher temperatures, particles are moving faster, so there are more collisions. Also and more importantly, the collisions are more energetic, and more collisions have energy greater than the activation energy, so the reaction is faster. On the graph this is shown that the higher the temperature the steeper the gradient therefore the reaction is faster, the collision theory backs up my conclusion; when the temperature gets higher the rate of reaction increases this is because the particles have more kinetic energy so they move around more so they collide more often.
In my prediction I was correct in predicting that the larger the surface area the faster the reaction will proceed. This was explained using the collision theory. So in my experiment the powdered calcium carbonate had the largest surface are, and therefore there were more collisions per second with the acid and the calcium carbonate. This can explains why powered calcium carbonate took the least time and why the large chips took the most time.
After the experiment, I regroup all my results in to a table. Therefore I start to work out the average of each reading I got. To find out the average of the readings. I added all three readings up and divided by three, and then I can find the average.
After I gathered all the average readings, I draw a line graph to show my result. In the graph, I can see that all the lines are positive correlation as this is what I predict at my prediction. In my prediction, I predict that as the temperature increase, the rate of reaction will decrease because the heated particles will gain more kinetic energy which has more chance of collision between reactant molecules.
I also draw another graph to show the rate of reaction at 60 sec in different temperature. I find rate of reaction by using the formula average/60=rate of reaction. To prove that the rate of reaction for each temperature, I find out the gradient of each temperature and compare it to the rate of reaction. Through this, I found out some anomalous result of the rate of reaction especially the rate of reaction at 20 and 40 degree. The gradient that I have find in 20 degree is 0.36 compare to the rate of reaction at 60 sec that is 0.15 which have a huge different between them. In 40 degree of the gradient is 0.69 whereas in rate of reaction at 60 sec is 0.47 which is so different.
In the graph, I can see that as the temperature increase, the line will go steeper and steeper. Whereas when the temperature is decrease, the line will become flatter and flatter.
At 60 degree, the gradient is 1.6 whereas at 10 degree, the gradient is 0.03. This clearly shows that the rate of reaction is faster at higher temperature which strongly supports my prediction.
The graph below show the rate of the reaction
The line has the classic shape of a rate of reaction graph. It starts off steep, becoming shallower until it levels off. This can tell the rate of reaction at any particular time by the slope (gradient) of the line.
The steeper the slope of the graph, the faster the reaction at that point. At the beginning, the reaction goes faster because there are more reactants to react. Whereas at the end, the reaction is slowing down because there are not enough reactants to react.
Evaluation
I think that the experiment went very well. This is because I got all the results that I expected and they look very conclusive. I felt I have accurate results to the best of my ability because I done it three times and done different temperature as well and so I am able to make a good conclusion. However, there are some anomalous results on the rate of reaction. As I find the rate of reaction in 20 sec to 60sec, I realise that some of the results went wrong as you can see in the graph. The rate of reaction should be increase as the time and temperature increase. But from my graph and the table, I can clearly see that in 60 degree, the rate of reaction is increase rapidly and then it start to decrease. Therefore I started to searching in my book and I found why this is happened. This happened because at the beginning of the reaction, there are more reactants in the reaction so that there will be more collision between them to react. Whereas at the end, there are not enough reactants to react so the rate of reaction decrease. Although I can explain this, but I cannot explain the result that I get in 30 and 40 degree which is highlighted in grey colour pen. But I think this is only the parallax error that make by the measurer. Also there are an anomalous result in the other graph in 30 degree, the line of it’s not a straight line. There is a bend in between 160 sec to 180sec. The line of it should be straight because in a higher temperature, the more faster the reaction and the quicker the carbon dioxide will be collected.
The procedure I used was quite safe (as long as the safety precautions were followed), and the results were quite similar to my predicted results, as they followed the trend, of the rate of the volume of gas being produced, increasing with an increase of the concentration.
The rate during the reaction does not stay constant, it changes throughout the reaction, and it’s greatest at the start but gets slower as the reaction proceeds. I think this is mainly to do with the fact the longer the reaction, has taken place, the more of the reactants react leaving fewer reactants with less chance of reacting.
The procedure was fairly accurate, considering the limitations of time and equipment. We had only few days to complete the preliminary and practical work for the investigation and the equipment was only what was available in school; the gas syringe was not digital, you had to make a judgement as to what the exact reading was whereas a digital one could have given a very precise reading. The stopwatch was also manually operated, so it was only as accurate as I was. The thermometer was also of traditional style; a digital one would have given a much better reading.
I can improve the method by using digital equipments to get the accurately result such as digital weighing scale to weigh carbon dioxide and digital thermometer to measure the temperature. Also I will increase the amount of acid from 20cm to 40cm so that the gas syringe can collect 100cm of carbon dioxide quickly.
The most common errors, which occur, are parallax errors, zero errors and reading errors.
Parallax Errors: The error, which occurs when the eye is not placed directly opposite a scale when a reading is being taken.
This must be taken in to account when measuring the CO2 level.
Zero Error: The error, which occurs when a measuring instrument does not indicate zero when it should. If this happens, the instrument's inaccurate "zero reading" should be subtracted or added from any other reading taken.
This must be taken into account when using the balance.
Reading Error: The error due to the guesswork involved in taking a reading from a scale when the reading lies between the scale divisions.
The amount of marble chip I put in each experiment are not the same. Although I am using the medium size of marble chip but there are also some powdered chip on it, so it makes the experiment unfair which affect the accuracy of the results I get from the experiment. Therefore, to ensure the result is accurate, I will weight the marble chip every time I do the experiment.
Also to make my result more accurate, I compared my readings to someone else reading from the class. I also made an average from my 3 result which will make my result more reliable.
The experiments were fair tests to a certain extent but there was a certain margin of error because the results recorded were only to the nearest cm³ and the values of the controlled variables were not exact amounts so the may have been slightly differently each time which would have affected slightly the reliability of the results. This would have made little difference to the results though as the volume of gas was only measured to the nearest cm. I think that there were enough evidence for me to drawup the conclusion.
To improved my experiment and make my result more accurate, I will increase every 5 degree to do the experiment and also I will extend experiment by changing the surface area and keeping the temperatures the same to investigate the effect of surface area on the rate of reaction because if I do that, I can have a strong evidence to support my prediction. Furthermore, I will change the concentration used so that I can see the effect of the concentration on rate of reaction which can help me to support my prediction. Moreover, I will use different catalyst because different catalyst has different effect on the rate of reaction.
