Orders from initial rates are a regular Paper 5 data-analysis question. Work through a student’s results for one of three reactions (an iodine clock, a bromate(V) clock or propanone and iodine): find each concentration from the dilution and each initial rate from the time, take logs, plot every cross yourself on the grid, circle the anomalous point, drag your own line of best fit and read its gradient. Then deduce both orders, write the rate equation, calculate the rate constant with its units and evaluate the method. Every attempt has different results and a different anomaly. Allow about 30 minutes.
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Why the total volume is kept the same with distilled water: then the concentration of the reactant you vary is proportional to its volume, and every other concentration stays fixed.
Concentrations from the dilution (stock × V / 50.00) and initial rates from the fixed change divided by t, both to three significant figures, and both log columns to two decimal places.
Every cross within half a small square, the anomalous point circled, a straight line of best fit through the other five points, two points read from your own line and far apart, the gradient to three significant figures and the order it shows.
The order of the second reactant from Table 2.2, a rate equation that uses your orders and the one given in the question, k from one good experiment, and its units from the overall order.
A reason for the anomaly that fits its direction, why a fixed timing uncertainty matters most for the fastest runs, and a change that really makes the results more reliable.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.