# chemistry coursework

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Introduction

Experiment to determine the factors which affect the rate of oxidation of acidified potassium iodide solution by hydrogen peroxide. Plan As described in my preliminary introduction I intend to carry out an investigation to determine the factors which affect the rate of oxidation of acidified potassium iodide solution by hydrogen peroxide. H202 + 2KI + H2SO4 = K2SO4 + 2H2O + I2 I intend to vary the amount of potassium iodide entered into the 100cm� solution (potassium iodide included in the solution). Potassium iodide is the independent variable. I plan to keep the volume of the solution at 100cm�. The dependant variable is time as this will vary depending on how quickly the solution turns a purple/black colour and the black cross marked on the paper below is not visible. I intended to keep the amount of sulphuric acid constantly at 40 cm� also keeping the amount of hydrogen peroxide at 15 cm� and the amount of special indicator at 5 cm�. In some cases where potassium iodide, sulphuric acid, hydrogen peroxide and the special indicator do not equal 100 cm�. Water is added to the solution to equal 100 cm�. . Potassium iodide is the independent variable therefore its volume must be changed in every solution. The apparatus required for this experiment consists of a stop clock, a 100 cm� beaker, a 100 cm� measuring cylinder, a 50 cm� measuring cylinder, a 10 cm� measuring cylinder and a glass rod. The diagrams of apparatus can be found on page 4. Method 1. Collect your apparatus. 2. Draw a black cross on a piece of paper using a marker pen. 3. When carrying out the experiment place this underneath the 100 cm� beaker. 4. Pour 40 cm� of potassium iodide and 40 cm� of sulphuric acid into the 100 cm� measuring cylinder. 5. Pour 15 cm� of hydrogen peroxide into the 50 cm� measuring cylinder. ...read more.

Middle

Temperature will affect the experiment as the higher the temperature, the faster the particles will move therefore more movement equals more collisions. The lower the temperature the slower the particles will move therefore less movement equals fewer collisions. Faster collisions will increase the rate of the reaction. At a higher temperature there will be more particles colliding with activation energy required break the initial bonds therefore the rate of the reaction will be faster. At a lower temperature there will be fewer particles colliding with activation energy required to break the initial bonds therefore the rate of the reaction will be slower. The apparatus I intend to use is suited to the experiment and will provide accurate and reliable measurements. The method I intend to follow is simple and easy to understand, allowing maximum achievement. Results Solution Volume of KI (in cm�) Volume of H2SO4 (in cm�) Volume of H202 (in cm�) Volume of special indicator (in cm�) Volume of H2O (in cm�) Time (in seconds) 1st / 2nd Averages (in seconds) Rate 1/time 1 40 40 15 5 0 26 / 23 24.5 0.041 2 30 40 15 5 10 44 / 41 42.5 0.024 3 25 40 15 5 15 34 / 34 34 0.029 4 15 40 15 5 25 58 / 61 59.5 0.017 5 10 40 15 5 30 140 / 138 139 0.007 Analysis My results show as the volume of potassium iodide in solution increases the rate and speed of reaction increase also. My rate and time graphs also show this. The rate line - graph shows a straight line passing through the origin. The 30 cm� volume appears to be slightly strange. The rate of this volume should have been much higher as the 25 cm� volume had a rate of 0.029. This result is anomalous. The rate of reaction should have been higher as the volume of potassium iodide was higher. ...read more.

Conclusion

The method would be the same, the only difference would be the solution would be contained in a conical flask and the volumes would be measure by using pipettes. My results provided sufficient evidence to support my conclusion. The only problem with my results is, human error is an obviously possibility. My results prove my conclusion, as the volume of potassium iodide increases the time of the reaction decreases and as the volume of potassium iodide decreases the time of the reaction increases. The rate of reaction increases as the volume of potassium iodide increases and the rate of reaction decreases as the volume of potassium iodide decreases. The anomalous result of 30 cm� of potassium iodide may have occurred because of the water left in the measuring cylinders after they had been washed, this may have affected the outcome of the solution. The measuring cylinders and the beaker were only washed with water, they were not rinsed with teepol, and residue from other substances may have remained in the beaker or measuring cylinders maybe explaining why this result was anomalous. Excluding this result my time - volume graph would have been a perfect curve. I think the line of best fit on this graph is correct but not precisely accurate. If all my results were as expected then the line would have been a perfect curve as I stated above. My results were very close to my lines of best fit. The line of best fit on the rate - time graph was very close to all of the results. I am very sure of this line of best fit. All the results are very close to either side of the line. My results are reliable but not one hundred percent reliable. If a computer was used in this experiment then the results would be very close to one hundred percent accurate. My results are approximately seventy percent accurate as they were all in ten percent of each other and four out of the five results matched the pattern I described in my conclusion. ...read more.

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## Here's what a teacher thought of this essay

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A well planned and conducted experiment with a detailed method. The analysis and explanation are slightly weaker with repetition of points and no attempt at quantitative analysis.

Marked by teacher Adam Roberts 14/10/2013