Rates of reaction - Hydrochloric acid.

Prediction

If I use a higher concentration (molar number) of hydrochloric acid in the reaction than there will be a higher volume of Carbon dioxide produced. In other words if I doubled the concentration of HCL it will result into an equal proportion of CO2 produced.

Hypothesis

I can back up my prediction by using the collision theory that I have come to know through my research.

Reacting Molecules must collide with one another

The reacting molecules must collide with sufficient energy

The reacting molecules must collide in an orientation that can lead to rearrangement of the atoms

It says the rate of reaction simply depends on how often and how hard the reacting particles collide with each other. By increasing the concentration of HCL I am increasing the chances of each of the particle of Calcium carbonate to collide with Hydrochloric acid molecules. When the collision theory says it should lead to rearrangement of atoms it means that the molecular structure should be altered (broken through the middle) and that is what I will try and do in the experiment (it might sometimes happen automatically if the other variables are controlled). The diagram below helps to explain this, the red particle in the diagram will be HCL in my case and the compound will be CaCo3.

If the acid is diluted with water it would make it weaker and also slower to react with the chips of calcium carbonate and because there are less particles of the reactant between the water molecules, which would have enabled it to make more collisions and therefore react quicker. Whereas if the solution has a stronger concentration with less water or none at all it would react at a faster rate, this is because there will be more of the particles reacting and colliding at a more faster rate than a solution with a weaker concentration and larger surface area.

Variables and Control

The variables that may have an effect in this experiment and need to be controlled are

The temperature- it increases the chances of collisions because particles are made to move faster and quicker as they gain heat energy. When the temperature increases, the average kinetic energy increases. As a result, the frequency of collisions between the particles increases. When two chemicals react, their molecules have to collide with each other with sufficient energy for the reaction to take place. This is collision theory. The two molecules will only react if they have enough energy. By heating the mixture, you will raise the energy levels of the molecules involved in the reaction. Increasing temperature means the molecules move faster.

Surface area-by increasing the surface area we are again increasing the chance of collisions by giving molecules more area to work on. For eg if a solid is broken down into smaller pieces or powder its surface area has been increased as it is obvious that there will be more walls to react with. The diagram that I have drawn explains it. Surface area is greater and more formula units are available to react. On the other hand, the same substance will react much slower when the substance is one large solid block. The formula units in the middle of the block cannot react until the outer part has reacted. Smaller particles have a bigger surface area than larger particle for the same mass of solid.

Catalyst- a catalyst works by giving the reacting particles a surface to stick to where they can collide with the opposite particles. There are two ways in which catalysts work. How fast a chemical reaction is depends upon how frequently the molecules collide this is called "kinetic theory". What catalysts are doing when they make a chemical reaction go faster is to increase the chance of molecules colliding. Adsorption is one way they do it. This occurs when a molecule sticks onto the surface of a catalyst, because the two molecules are held so close together, it is more likely that they will collide and therefore react with each other. Intermediate Compounds the chemicals involved in the reaction combine with the catalyst making an intermediate compound, but this new compound is very unstable. When the intermediate compound breaks down it releases the new compounds and the original catalyst.

Concentration- If the acid is diluted with water it would make it weaker (in number of HCL particles it has) and also slower to react with the chips of calcium carbonate and because there are less of the reactant particles between in HCL when it is diluted with water as water replaces the HCL particles. And if I was to think about it as a room packed with boxes there would a less chance of me seeing the other components of the room such as the window ie I have a less chance of seeing them. Increasing the concentration means there are more particles of reactant knocking the opposite particles. Increasing the concentration of the reactants will increase the frequency of collisions between the two reactants. So this is collision theory again. Because more of the acid will be present for each separate chip, more of the surface area will be covered which means more of the acid will be acting upon it and this would hence result in an increase in the rate of reaction.

Mass of CaCo3-increasing the mass of CaCo3 will mean that there will be more particles and surface area for the HCL molecules to collide with and therefore more of HCL will be needed to react with each particle of CaCo3 therefore resulting in an unequal proportion of reaction. If I were to decrease the mass of the marble chips than there would be less of HCL particles required to react with a few of the marble chips and therefore meaning that it wont be balanced.

Volume of HCl-has to remain constant because increasing it will mean that you ...

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Mass of CaCo3-increasing the mass of CaCo3 will mean that there will be more particles and surface area for the HCL molecules to collide with and therefore more of HCL will be needed to react with each particle of CaCo3 therefore resulting in an unequal proportion of reaction. If I were to decrease the mass of the marble chips than there would be less of HCL particles required to react with a few of the marble chips and therefore meaning that it wont be balanced.

Volume of HCl-has to remain constant because increasing it will mean that you are increasing the number of particles present and thus it may react with marble chips in a much faster rate.

Time- has to be controlled because if the rate of reaction will slowly decrease as all the particles have already collided and lost their energy.

Preliminary work

This helped me a lot in deciding how much of the marble chips should I use (grams), it helped me to decide upon the amount of HCL to be used (volume), it also gave me an idea on how long I should keep the experiment going (minutes or seconds), it helped me to decide upon a suitable range of Molar of HCL to be used (concentration M). I also came to find out that Surface area of the conical flask will also affect the rate at which the reaction takes place. If the flask has got a small base, the acid and the marble chips will be more packed together, meaning that the acid is closer to the chips surrounding it thus covering a larger surface area of particles. With the chips closer together it means that the collisions will occur more often because the particles will not loose their energy travelling to another particle otherwise the collisions will be less.

I have used trial and error to reach certain conclusions about the procedure. Below are the results that I gained from the initial experiments:

Method

My basic method for the experiment will be to alter the rate of reaction by changing the concentration of HCL. The concentration levels are 0.5M, 1M, 1.5M, 2M and 2.5M. When I vary the concentration of the acid i.e. is diluted with water it would make it weaker (in number of HCL particles it has) and also slower to react with the chips of calcium carbonate as there are less of the reactant particles between in HCL when it is diluted with water as water replaces the HCL particles. Increasing the concentration means there are more particles of reactant knocking the opposite particles. Increasing the concentration of the reactants will increase the frequency of collisions between the two reactants. So this is collision theory again. Because more of the acid will be present for each separate chip, more of the surface area will be covered which means more of the acid will be acting upon it and this would hence result in an increase in the rate of reaction.

I will measure the amount of carbon dioxide produced because this is the best way to measure the rate/speed of a reaction. Before carrying out the actual experiment, I will do some preliminary work where I will use trial and error to improve efficiency.

The variables that I have talked about in detail above have to be controlled as we can see how each one of them can alter the rate of reaction and therefore they might lead to wrong results and conclusions need to be controlled in order to have a fair test and accurate results; therefore I will make sure that the temperature in which I do the experiment should be constant and normal room temperature 27 C and again this is because it increases the chances of collisions because particles are made to move faster and quicker as they gain heat energy. When the temperature increases, the average kinetic energy increases. As a result, the frequency of collisions between the particles increases. When two chemicals react, their molecules have to collide with each other with sufficient energy for the reaction to take place. This is collision theory. The two molecules will only react if they have enough energy. By heating the mixture, I will raise the energy levels of the molecules involved in the reaction. Increasing temperature means the molecules move faster.

I will only use the same size of CaCo3 each time(i.e. I have carefully select them because by increasing the surface area we are again increasing the chance of collisions by giving molecules more area to work on. For eg if a solid is broken down into smaller pieces or powder its surface area has been increased as it is obvious that there will be more walls to react with. The diagram that I have drawn explains it. Surface area is greater and more formula units are available to react. On the other hand, the same substance will react much slower when the substance is one large solid block. The formula units in the middle of the block cannot react until the outer part has reacted. Smaller particles have a bigger surface area than larger particle for the same mass of solid.

The mass of marble chips also has to be controlled because increasing the mass of CaCo3 will mean that there will be more particles and surface area for the HCL molecules to collide with and therefore more of HCL will be needed to react with each particle of CaCo3 therefore resulting in an unequal proportion of reaction. If I were to decrease the mass of the marble chips than there would be less of HCL particles required to react with a few of the marble chips and therefore meaning that it wont be balanced.

The volume of HCL will always have to stay constant because increasing it will mean that I am increasing the number of particles present and thus it may react with marble chips in a much faster rate.

I will not use a catalyst at any time of the experiment because it gives the reacting particles a surface to stick to where they can collide with the opposite particles. There are two ways in which catalysts work. How fast a chemical reaction is depends upon how frequently the molecules collide this is called "kinetic theory". What catalysts are doing when they make a chemical reaction go faster is to increase the chance of molecules colliding. Adsorption is one way they do it. This occurs when a molecule sticks onto the surface of a catalyst, because the two molecules are held so close together, it is more likely that they will collide and therefore react with each other. Intermediate Compounds the chemicals involved in the reaction combine with the catalyst making an intermediate compound, but this new compound is very unstable. When the intermediate compound breaks down it releases the new compounds and the original catalyst.

Time limit will be one minute because the rate of reaction will slowly decrease as all the particles have already collided and lost their energy.

When I am pouring the HCL into the flask I have to be careful not to let any drip because it will reduce the amount of HCL later present in the reaction. I also have to make sure that the gas syringe is parallel to the surface of the table because if it is tilted down wards may be the force of gravity will act on the piston and pull it faster which may lead to wrong results, and if it is tilted upwards than the force of gravity will act on the piston pulling it and making it harder for CO2 to push the syringe/piston. I also have to make sure that throughout the experiment I do not mix or shake the flask because it may disrupt the particles colliding and sometimes I might even increase the chance of colliding and I don’t want this to happen because it is going to generate artificial results and not natural.

I carried out the experiment in a group of four pupils. We setup the apparatus and poured the HCL solution and put the marble chips and without delay blocked the flask with the rubber bung and simultaneously started the stopwatch. The tasks in the group were evenly spread and each student specialized in something i.e.

-Pupil 1 – pours the HCl solution in the beaker and then into the measuring cylinder( in order to stop any spillage and for accurate measurement and efficiency)

-Pupil 2 – washes and dries the conical flask (dries it in order to remove water particles which might decrease the concentration of HCL when reacted with marble chips)

- Pupil 3 – puts the marble chips first because if it was put later they would not sink easily and therefore the top surface area of the marble chips will stay unreacted.

-Pupil 4 – starts the stop watch simultaneously and stops it after one minute because time is an important factor that affects the rate of reaction(because I know if we leave the reaction for longer than planned than the reactants molecular energy will be lost and therefore the rate of reaction will decline gently.

The only factor that I could not control was the room temperature; this is because I did not have the right instrument to measure it. I did not have a room thermometer.

Apparatus

I will use the following equipment

Side arm flask- to attach the gas syringe tube and try not to lose any gas
Gas syringe- to measure the volume of Co2 (product)
Electrical balance- to obtain accurate measurements of the weight of marble chips
Stand- to hold the flask and the syringe in place (explained in paragraph 8 of method)
Measuring cylinder- to measure the amount of HCL to be poured into the flask for the reaction to take place.
Rubber bung- to stop the gas from escaping into the air
Stop watch-to time the reaction (as time is one of the main variables otherwise it might lead to wrong results).

Safety

We will take extra precautions while dealing with acids, because they may harm if they are swallowed and there will be a strong reaction taking place and therefore everyone will need to wear goggles.

Detailed method

For each level of concentration of HCL. I will put an equal amount of marble chips which are of the same size, shape and mass by using an electric balance. I will also pour the same volume of HCL by using a measuring cylinder. I will make sure that when I react the materials I do it in a correct way i.e. the particles of Marble chips colliding correctly with HCL particles. I will even make sure that the gas syringe is parallel to the table because if it is tilted in anyway the results wont be correct the force of gravity will be acting upon the piston of the syringe therefore either pressing carbon dioxide back to the flask or maybe even move outwards in a very fast rate due to gravity pulling it. I will leave the reaction to take place only for a minute and I will repeat the whole experiment twice so that a reliable set of results can be obtained.

Results

For graph turn over

Analysis and conclusion

From the graph and the chart I can see that there is a pattern/relationship in the concentration of HCL and the amount of carbon dioxide produced. The relationship is that the higher the level of concentration of HCL will equal to a proportional (not directly proportional) amount of Co2 produced. It can be seen that the highest concentration (2M) had the highest reaction rate and reached 190cm3, where as the lowest concentration (0.5M), only reached a maximum of 25cm3.

From the evidence that I have collected I conclude that if I increase the concentration of HCL when reacted with marble chips the amount of Carbon dioxide produced will increase. This is because higher concentration of HCL will have more particles surrounding the marble chips and therefore it may result into more successful collisions. By increasing the concentration I am satisfying the collision theory in three ways,

1) Increase in concentration will mean that particles will surround the CaCo3 particles and consequently rearrange them (The reacting molecules must collide in an orientation that can lead to rearrangement of the atoms)

2) The particles naturally have some form of energy stored in them which helps them to keep them bonded with the same atoms, therefore when I react them they release this energy and hence have adequate energy to move and to collide. (The reacting molecules must collide with sufficient energy)

3) Increasing the concentration will apparently mean that the HCL will collide with CaCo3 (Reacting Molecules must collide with one another)

I predict if I use a higher concentration of HCL say 3M than I can predict what amount of CO2 will be produced. 0.5M is 21, 1M is 43, which is almost the double, and 1.5M is 90 which is almost the double of 43. 2.5M is 387. (387 X 2 = 774)

The prediction I made earlier to some extent corresponds with the conclusion. It matches because I had mentioned that a higher concentration will produce a higher amount of CO2 which will be proportional to concentration, but in the conclusion I haven’t mentioned the proportion to which it is produced because I came to know from the results that even though the product doubles every time (21,43,90,189,387) the concentration doesn’t double (1,1.5, 2, 2.5), therefore to some extent the prediction does not match the conclusion. It’s not a complete match

Evaluation

The procedure worked very well because I can see that the results obtained were in a pattern that I had expected, there were no anomalies found and there were very slight variations when I repeated the experiments

The results that I derived from the experiments showed a pattern and the prediction that was made was correct. but it was probably due to the surface area of the marble chips because of not being selected carefully from a range of sizes, varying from 0.5cm3 to powder.

Even though the results showed the relationship between HCL concentration and Carbon dioxide produced, there were some variations in the experiments such as 24, 21, 19 and 87, 90, 93. These results had a maximum difference of upto 6 cm3. The reason for this could be the surface area of the marble chips. The marble chips were picked up after checking their sizes and sides but this could not have been so accurate because we are human beings but it could have been done by crushing them into powder which will mean that they would all be the same size and perhaps have the same surface area. What I could do is use a grinding machine and grind them completely to the extent that they become fine particles. The other reasons for these variations could be to a certain extent the temperature and

Overall the results that I obtained were to a great extent reliable, although there were a number of variations. I think if I were to do this experiment again I would attain almost the same results but with minimal variations.

In my conclusion I have mentioned if the concentration is increased than the amount of carbon dioxide produced will increase. Note that I have only mentioned “increase”, and each point in my chart clarifies that. Each point clearly increases as the concentration is increased. Experiment 1: 24, 42, 87, 190, 391. Experiment 2: 21, 45, 90, 187, 389. Experiment 3: 19, 41, 93, 192, 382.

I did not attain any anomalies because I think that the experiment was done with precision and skills, we had specialized tasks and the accuracy was kept under control (paragraph 10 of method. e.g. placing the gas syringe correctly.).

For my extension work I could do another experiment in which I could vary the concentration again in order to increase the reliability of this experiment.

Bibliography

CGP-The Revision guide Final Exam

www.ncpublicschools.org/curriculum/ science/Chemistry/chem.htm

EFFECTS OF CONCENTRATION ON RATES OF REACTION

Prediction

From the investigation that I carried out before, I have come to know that the higher the concentration the faster the rate of reaction.

Hypothesis

Higher concentration of a solution will have more particles of reactants colliding each other, however successful reactions will only take place when these particle hit with the right amount of energy (kinetic) and the direction they hit the opposite particles. In the first part of the investigation I have explored this in greater detail. A diluted solution of Sodium Thiosulphate will take longer to react because there will be less Sodium Thiosulphate particles that HCL particles should collide with, instead there will be water molecules replacing Sodium Thiosulphate particles.

Apparatus

Conical flask
Measuring cylinder X2
Paper
Pencil
Beaker X2
Sodium Thiosulphate solution
HCL solution

Method

The two reactants I will use are Sodium Thiosulphate and dilute Hydrochloric Acid. I will pour 50cm3 of Sodium Thiosulphate and 5cm3 of HCl into a conical flask and shake it until the solution turns cloudy and the X mark that I crossed earlier on a paper won’t be seen, thus I will measure the time taken for the X to disappear. I will change the concentration of sodium Thiosulphate by adding water to it.

Setup

Fair experiment

To make this experiment fair in order to get the right conclusion and evidence I will have to keep the following variable that affect rates of reactions. This means I will keep the temperature constant i.e. room temperature, the concentration of HCl should not be altered i.e. 5cm3, I will make no use of a catalyst.

Accuracy

I will make sure that when I take any reading I read from the lower line of water, because of the meniscus.

I will have to make sure that I have a pair of measuring cylinders, one for sodium Thiosulphate and one for HCL and use a 50cm3 cylinders for Thiosulphate and a small one of 10cm3 for HCL. I will have to repeat each experiment thrice in order to get reliable and fair results. I also have to start the clock immediately after mixing the chemicals. After every experiment I have to wash and wipe the conical flask. One of the most important things to consider is that when changing the paper on which the cross is marked and using a new one, I have to make sure that the grade of the cross is the same again i.e. it shouldn’t be any darker or lighter.