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Rates of reaction - Hydrochloric acid.

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Introduction

RATES OF REACTION 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 CO[2 ]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 CaCo[3.] [image003.gif] 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. ...read more.

Middle

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 CaCo[3] 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 CaCo[3] 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. ...read more.

Conclusion

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 0.5cm[3] 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 cm^3. 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. ...read more.

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