Persulphate and Potassium Iodide Essay Example for Free

Persulphate and Potassium Iodide Essay The rate of which the reaction happened can be found out by using the simple formulae: Speed = Distance Time Distance is what we call the persulphate because we are measuring the amount of persulphate needed to react. The amount of persulphate will always be the same at the end so it doesnt matter how much we use. So to make it easy we can call this 1 (unit). Therefore Rate = 1 Time Therefore rate is the inverse of time and we can draw a graph of this. The faster the rate of reaction takes place, the shorter is the time needed for the reaction to finish. To be more precise, the speed of the reaction is inversely proportional to the time taken for the reaction to finish. In my prediction I stated, I predict that when the concentration of the reactant, Potassium Persulphate, is increased while all other factors are kept constant then the rate of reaction will increase. From the graph we can clearly see that this is the case. At 5% concentration the rate of reaction is very slow as it takes 720. 29 seconds for the cross to disappear but at 100% concentration the rate of reaction has increased dramatically and is very fast, taking only 16. 12 seconds for the cross to disappear. From my predicted graph, we can see that it is very similar to that of the actual graph and therefore my prediction has been supported by the experiment. In this experiment only one concentration was altered. A variation is to keep the concentration of iodide constant and alter the concentration of Potassium persulphate. Then the speed of the reaction is found to be proportional to the concentration of the Persulphate. If the Persulphate concentration is doubled then the speed doubles. The reason for this is that the ions are closer together in a concentrated solution. The closer together they are, the more often the ions collide. The more often they collide, the more chance they have of reacting. Collision Theory for Rates of Reaction Before looking at the factors that can alter the rate of reaction, we must consider when happens when a reaction takes place. First of all, the particles of the reacting substances must collide with each other and, secondly, a fixed amount of energy called the activation energy must be reached if the reaction is to take place. If a collision between particles can produce sufficient energy (i. e.if they collide fast enough and in the right direction) a reaction will take place. Not all collisions will result in a reaction. A reaction is speeded up if the number of suitable collisions is increased. Effect of Temperature on the Rate of Reaction When one of the reactants is a solid, the reaction must take place on the surface of the solid. By breaking up the solid in to smaller pieces, the surface are is increased, giving a greater area for collisions to take place and so causing and increase in the rate of reaction. This explains why mixtures of coal dust and air can cause explosions. The experiment was done on the same day trying to keep the temperature the same. Effect of Light on the Rate of Reaction The rates of some reactions are increased by exposure to light. Light has a similar effect, therefore, to increasing temperature. This is why the paper had to be used. Effect of Concentration on the Rate of Reaction The more concentrated the reactants, the greater will be the rate of reaction. This is because increasing the concentration of the reactants increases the number of collisions between particles and therefore, increases the rate of reaction. This also explains why the greatest rate of reaction are usually as soon as the reactants are mixed i. e. they are both at their highest concentrations. As the reaction precedes the concentrations of the reacting substances decrease and the rate of reaction decreases. The effect of concentration is shown in this experiment using potassium persulphate and Iodine showing a colour change and cloudiness due to the precipitation of potassium. Effect of Light on the Rate of Reaction The rates of some reactions are increased by exposure to light. Light has a similar effect, therefore, to increasing temperature. Thats why paper is used to surround the beaker. Effect of Catalysts on the Rate of Reaction A catalyse is a substance which can alter the rate of a reaction but remains chemically unchanged at the end of the reaction. Catalysts usually speed up reactions. A catalyst, which slows down a reaction, is called a negative catalyst or inhibitor. Catalysts speed up reactions by providing an alternative pathway for the reaction, i. e. one that has much lower activation energy. More collisions will, therefore, have enough energy for this new pathway. So the factors, which affect the rate of a chemical reaction, include: 7. Concentration 8. Particle Size 9. Pressure (for reactions involving gases) 10. Temperature 11. Light 12. Presence of a catalyst The difference in the rate of reaction can be explained in terms of a simple collision theory. Evaluation The procedure used wasnt the most accurate procedure but it was good enough to give us firm enough results and conclusion. The experiment shows a reasonably high accuracy of results to a hundredth of a second. Although, when dealing with the solutions it was taken to the nearest cm3. This was because we only had equipment to this degree although it was good enough to give accurate results. The experiment has shown to produce no anomalous results. As you can see from the graph that all the results follow the line of best fit and none seem out of place. I think the experiment shows quite a high standard of reliability. The preliminary experiment showed that the right amount of starch was used and even when repeated no anomalies were found. I can say therefore from this that I can support a firm conclusion. There are only a few things that could produce anomalous results. If the constants were not kept constant then this may produce some misleading results. This was done as best of our abilities although if a different batch of starch was used through the experiment this would produce inaccurate times also if the pipettes were accidentally mixed up or the observer of the cross changed or stopped the clock not as accurately as before. The number of results taken from the experiment though was a suitable number, although to make it a lot more accurate the results could have been repeated 3 times and then an average taken, although this would take a long time. This experiment has shown to be very suitable for its purpose and given some accurate and reliable results. If, for any instance, it was necessary to have extremely high accurate results the experimental procedure may have to be changed. If this experiment were to be changed in any way it would only be to do more repeat readings and measure and time more accurately; this then would give more accurate results. Improvements outside the school laboratories, with this experiment, can be changed by using very accurate equipment. Keeping all things, which affect the rate of reaction constant, for example light and temperature. If done in a cabinet with a thermometer and light sensor these two things can be kept constant to a high degree. By observing a colour change can be improved by a colour detection sensor. Fresh solutions in apparatus, which is cleaned thoroughly after use an also using a photocell linked into a clock rather than the visual way These differences can produce some very highly precise results. Chemistry: Scientific Investigation.