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Introduction

CHEMISTRY LAB REPORT Research Question Find the rate expression for a reaction between propanone and iodine Background Information The rate of reaction can be defined as the "increase in molar concentration of a product of a reaction per unit time" or the "decrease is molar concentration of a reactant per unit time." A quantitative way of showing this is through the rate expression. We can find this by performing a series of experiments: changing the concentration of one of the reactants whilst keeping the others constant. For example: A + B - C The reaction above would have the rate expression R (rate of reaction) = k [A] x [B] y Where: * The rate of reaction is measured in mol dm-3 s-1 * [A] [B] is the product of the concentrations of the reactants measured in mol dm-3 * x and y are the powers which the concentrations are raised to, as well as the order of reactants A and B. They usually have values between 0 and 2 * k is the rate constant, with varying unites dependant upon the order of the reaction * the over all order of the reaction is x + y The equation giving the reactions we will consider is: DILUTE H2SO4 CH3COCH3 (aq) + I2 (aq) � CH3COH2I(aq) + HI(aq) (Dilute sulfuric acid is used as a catalyst as the reaction is quite slow) ...read more.

Middle

Next add the iodine, starting the stopwatch as soon as the last drop is added. * Swirl once and leave the solution to react, observing from above. * Once the solution is colorless, stop the stopwatch and record the time. * 4 other different concentrations of propanone should be taken, with 2 trials for each concentration taken. * The other concentrations will be made by adding distilled water, with the total volume of propanone remaining the same. 30ml propanone and 5ml water, then 25ml propanone and 10ml water, the 20ml propanone and 15ml water, then 15ml propanone then 20ml water. Data Collection Experiment 1: Changing the concentration of Iodine Conc I2 (mol dm-3) Volume I2 (dm3) Moles I2 (mol) Vol H2SO4 (dm3) Volume Propanone (dm3) 0.0038 0.005 0.000019 0.010 0.035 0.0076 0.005 0.000038 0.010 0.035 0.0114 0.005 0.000057 0.010 0.035 0.0142 0.005 0.000071 0.010 0.035 Time (Trial 1) (s) Time (Trial 2) (s) Rate for trial 1 (1/time) Rate for trial 2 (1/time) Average rate (2dp) 120 121 0.0083 0.0082 0.01 127 129 0.0079 0.0078 0.01 135 135 0.0074 0.0074 0.01 141 140 0.0070 0.0071 0.01 The four concentrations of iodine were already given to me, along with the 1M solutions of propanone and H2SO4. I worked out number of moles using the formula: Moles = concentration x volume Observations: The time taken for the reaction was similar for all concentrations of iodine, and therefore the average rate. ...read more.

Conclusion

For zero order, the graph should have no slope For first order, the graph should have a straight line For second order, the graph should give a curve As iodine had no slope, and both propanone and sulfuric acid gave straight-line graphs, I can conclude that the order for each of the reactants is as follows: Iodine: zero order Propanone: first order Sulfuric acid: first order Overal order = 1 + 1 + 0 = 2 The rate expression can therefore be defined as Rate = k [CH3COOH] [H2SO4] Evaluation Since the rate expression found from my calculations qualified with the theoretical rate expression, my experiment was successful in its aims. There was, however, room for improvement to reduce the margin for error: Systematic Errors * These produce results that fluctuate by a fixed amount from the true results. This can be viewed in the graphs for changing the concentration of propanone as well as sulfuric acid, as the line of best fit did not pass through the origin. This could have been avoided by checking that all measuring instruments were correctly calibrated. Random Errors * These are dependant on the precision of the measuring instruments, so using stopwatches and measuring cylinders to a smaller degree would reduce this, also not eliminating it completely. * Error in time could also have been minimized by taking by more trials to obtain a more accurate value overall. * Measuring from the bottom of the meniscus each time could have also reduced parallax error due to the measuring cylinder. ...read more.

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