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Investigation to see how the concentration affects the rate of reaction.

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Introduction

Investigation to see how the concentration affects the rate of reaction Aim: To find out whether the concentration affects the rate of reaction. Collision theory: The theory that we use to explain how different variables change the rate of reaction is called the collision theory. For a reaction to take place, the particles of the substance that are reacting have to collide. If they collide with enough energy then they react. The minimum amount of kinetic energy that two particles need if they are going to react is called the activation energy. There are therefore two main ways of increasing the rate of reaction: 1) Increase the number of collisions 2) Increase the amount of movement (kinetic) energy so that more collisions lead to a reaction. The four main variables that can change the rate ofreaction are: 1) The concentration of the substances reacting 2) The temperature 3) The size of the particles 4) A catalyst being present Invertase is an enzyme which works best at body temperature (37 degrees Celsius). It is also a biological catalyst. The word catalyst means an added substance, in contact with the reactants, that changes the rate of a reaction without itself being chemically changed in the end. There are two types of catalyst; a 'positive catalyst' speeds up the rate of reaction. However, a 'negative catalyst' slows down the rate of reaction. Invertase is a positive catalyst. Catalysts increase the rate of a reaction by helping break chemical bonds in reactant molecules and provide a 'different pathway' for the reaction. ...read more.

Middle

I will maintain a constant temperature in the water bath so not to affect the number of collisions between each molecule, I will also keep the same volume of solution in each test tube, I will wash pipettes through thoroughly before filling each test tube, I will wear gloves to prevent contamination, and finally I will use distilled water to prevent any impurities. During my experiment I will need to keep both water and sucrose constant. I will change the concentration of invertase throughout a series of 5 or 6 tubes so that the change in results can clearly be seen. For my experiment I will use a maximum concentration of invertase of 1% and a minimum of 0%. I will take 6 readings in even steps, increasing by 0.2% each time to make sure each part of the range is investigated. Therefore my readings will be taken at o%, 0.2%, 0.4%, 0.6%, 0.8%, and 1%. I will use the following calculation to work out the concentration of the invertase solution: Volume of invertase used X 1% = concentration of invertase solution Volume of invertase used + Volume of distilled water used Below is a table showing my preliminary calculation based on 5(cm3) of solution: Volume of 1% invertase solution (cm3) Volume of distilled water (cm3) Calculation Concentration of invertase solution (%) 5 0 5/5x 1% 1 4 1 4/5 x 1% 0.8 3 2 3/5 x 1% 0.6 2 3 2/5 x 1% 0.4 1 4 1/5 x 1% 0.2 0 5 0/5 x 1% 0 Method of preliminary experiment: (Note: do each test tube one at a time) ...read more.

Conclusion

* Inaccurate volumes of the solutions, due to mistaken measurement of the solutions. * The level of cloudiness may have been interpreted differently by different people. * The temperature may not have remained constant throughout each experiment. * The concentration of invertase may have still been too small a percentage and therefore incorrectly measured. * It may have been difficult to read the level of solution on the test tube due to refraction. To improve my results I would change the following: 1. Firstly I could use a colorimeter which gives a far more accurate reading for cloudiness compared to judging by eye. However if this equipment was unavailable I would also make sure that the same person judged it each time therefore to prevent inaccurate results as peoples opinions may vary on when the solution has turned cloudy. 2. I would also leave the thermometer in the water throughout my experiment enabling me to check the water bath temperature is remaining constant. 3. To also have more accurate measurements of each solution I would use greater volumes making it easier to measure. 4. Furthermore I could use a burette to measure out the volumes of solution which may help to improve accuracy. Overall my results where fairly reliable; they allowed me to see the relationship between the concentration of invertase and the rate of reaction, which lead me to conclude that my prediction was correct. I could now go on to study other factors which could affect the rate of reaction, for example temperature, size of particles, a catalyst being present, ect. ?? ?? ?? ?? 1 ...read more.

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