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To find out the effect of varying concentration of potassium iodide in a I2 / H2O2 reaction

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LAB REPORT - KINETICS Effect of Concentration (I2 / H2O2 reaction) Aim To find out the effect of varying concentration of potassium iodide in a I2 / H2O2 reaction on its reaction rate Hypothesis In this reaction between hydrogen peroxide and potassium iodide, the amount of hydrogen peroxide is kept constant while the amount of potassium iodide is changed. There are two stages that happen in this reaction. In the above reaction, hydrogen peroxide is broken down into water molecules. The iodine ions from potassium iodide are converted into iodine molecules. When sodium thiosulphate reacts with starch and uses it up, it starts reacting with iodine molecules instead, converting them back into iodine ions. Therefore the iodine ions are not used up in the reaction until all the sodium thiosulphate reacts. However, the excess iodine molecules cannot be converted back into iodide ions and react with starch instead to produce a blue colour. I predict that when the solution turns blue, the reaction has finished. An excess of acid is present in the reaction mixture so that the decrease in the acidity caused by reaction (1) ...read more.


water 30 35 40 45 50 measuring cylinder 5. 0.1M Na2S2O3 10 10 10 10 10 pipette 6. '2 volume' H2O2 20 20 20 20 20 pipette Total volume 145 145 145 145 145 (3) Take the measured chemicals 1 and 2 in a beaker, 3 and 4 in another separate one, and 5 and 6 in yet another beaker (4) First mix chemicals 1 and 2, and 3 and 4, into a conical flask. (5) Then mix the 5 and 6 into the solution and immediately start the stopwatch. Swirl the solution only once and record the time it takes for the solution to turn blue. (6) Repeat the experiment, taking other values for volumes, such as in Expt A to E. Data Presentation Experiment Volume of KI/cm3 � 0.05 cm3 Time/s � 0.5s A 25 51.06 B 20 60.03 C 15 74.00 D 10 87.63 E 5 110.26 Data Processing There were a few uncertainties in the equipment that we used. At first, the systematic and random error values must be calculated. The uncertainties were given on each of the measuring instruments that we used. ...read more.


Error in measurement: Percentage error (%) = 3.20% Therefore, 3.20% of 0.0222 � 0.0007 Therefore the rate constant = 0.0222 � 0.0007 Literature value = 0.018 Therefore, total error = Conclusion By plotting a graph of volume against time, we can find the half-life of the reaction. The graph was found to be a curve with a constant half-life. This indicated that the reaction was a first-order reaction. The error in this reading can be caused mainly by human errors in taking readings or using wrong methods - example, it could be difficult to time the reaction properly. Taking an average is a good way to reduce this error. By plotting a graph of rate against concentration, the rate constant k was found to be about 0.0222. Here also the error in measuring time would give wrong readings of the rate constant. The percentage systematic error was found to be quite small. There could have been an error in calculating the percentage error. However, the error between the experimental and literature values is very large: 23%. Even the error bars of the systematic error of 0.0007 do not compensate for the error. This could be due to faulty equipment. * For further experiments, investigate the effects of performing the experiment at different temperatures. ...read more.

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