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An Investigation into the effect of concetration on the Rate of Reaction Between Potassium Persulphate and Potassium Iodide.

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Introduction

AN INVESTIGATION INTO THE EFFECT OF CONCETRATION ON THE RATE OF REACTION BETWEEN POTASSIUM PERSULPHATE AND POTASSIUM IODIDE The rate of a chemical reaction is a measure of how fast of how slow the reaction takes place. It is important to remember that a rapid reaction is completed in a short time. Some reactions are very fast, e.g. the formation of silver chloride precipitate when silver nitrate and hydrochloric acid solutions are mixed. Other reactions are very slow, e.g. the rusting of iron. For practical reasons, reactions used in the laboratory for studying rates of reactions must not be too fast or too slow. Having selected a suitable reaction it is necessary to find a change that can observed during the reaction. An estimate of the rate of reaction can be obtained from the time taken for a measurable change to take place. Suitable changes include: 1. Colour 2. Formation of precipitate 3. Change in mass (e.g. A gas evolved causing a loss of mass) 4. Volume of gas evolved 5. Time taken for a given mass of reagent to disappear 6. pH 7. Temperature In following experiment I will be investigating the time of the reaction between Potassium Persulphate and Potassium Iodide. By adding starch indicator to the reaction, at the start, there will be a distinctive colour change when the two substances react. This is because of the reaction with iodide turns the solution blue/black when reacted with the starch indicator. Therefore the solution will change colour and it can be timed how long it takes to change colour and go cloudy or how long a cross drawn underneath takes to disappear when viewed through the solution, using different concentrations. Equation of reaction: Potassium + Potassium Potassium + Iodine Persulphate Iodide Sulphate K2 S2 O8 (aq) + 2KI (aq) 2K2 SO4 (aq) + I2 (s) Prediction 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 ...read more.

Middle

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: 1. Concentration 2. Particle Size 3. Pressure (for reactions involving gases) 4. Temperature 5. Light 6. Presence of a catalyst Certain aspects must be kept constant to ensure a fair test, these include: 1. Repetition of experiment with averages taken 2. Concentration of the 0.05M (10cm3) KI 3. Amount of starch (3ml) 4. The same cross each time 5. Temperature 6. Amount of light entering the beaker 7. The distilled water must be the same 8. The beaker the same 9. The amount of agitation 10. Time you start the stop watch 11. The person who starts the stop watch and times the reaction 12. The height of the eye/viewing above the coin Line graph of expected results Obtaining Evidence During the experiment all equipment was used safely with precision and skill giving successful results. Below shows the time taken for the cross to disappear when a varied concentration of Potassium Persulphate was reacted with Potassium Iodine and the starch. Concentration of Potassium Persulphate (K2S2O8) (%) Concentration of Potassium Iodine (KI) (10cm3) Amount of starch (cm3) Time (Seconds) 100% 0.05M 0.1 16.12 95% 0.05M 0.1 19.60 90% 0.05M 0.1 22.69 85% 0.05M 0.1 28.01 80% 0.05M 0.1 33.13 75% 0.05M 0.1 38.22 70% 0.05M 0.1 49.30 65% 0.05M 0.1 52.31 60% 0.05M 0.1 55.24 55% 0.05M 0.1 56.89 50% 0.05M 0.1 59.34 45% 0.05M 0.1 75.02 40% 0.05M 0.1 91.44 35% 0.05M 0.1 107.65 30% 0.05M 0.1 120.11 25% 0.05M 0.1 145.72 20% 0.05M 0.1 215.44 15% 0.05M 0.1 288.92 10% 0.05M 0.1 420.37 5% 0.05M 0.1 720.29 Analysing Evidence A basic explanation of what has been found out is that as the Potassium Persulphate concentration increases, the rate of reaction increases. The line of best fit is drawn through virtually all the points so there are no obvious anomalous results. ...read more.

Conclusion

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 ...read more.

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