Chapter 7 Rate of chemical reactions Section 7.1 Investigating the rate of chemical reactions Experiment 7.1.1 Measuring the rate of reaction Purpose To measure the rate of reaction and investigate the effect of particle size and concentration on the rate. Theory Marble chips are composed of the ionic compound calcium carbonate. When chips are added to a hydrochloric acid solution the reaction that occurs produces carbon dioxide gas. Provided that no liquid 'spray' is able to leave the flask in which the reaction occurs, only carbon dioxide gas will be lost from the flask as the reaction proceeds. The equation for the reaction is: 2HCI(aq) + CaCo,(s) → CaCl,(aq) + H,0(1) + CO,(g) The mass loss is equal to the mass of carbon dioxide evolved. Duration 40 minutes Materials 40 ml 2.0 M hydrochloric acid (HCI) 20 ml 1.0 M hydrochloric acid (HCI) 40 g large marble chips 20 g small marble chips (do not use powdered chips) 3x 100 ml conical flasks 100 mL measuring cylinder 50 mL beaker cotton wool electronic balance computer and spreadsheet program (optional) Safety Wear safety glasses and a laboratory coat for this experiment. Hydrochloric acid solutions are corrosive and are an irritant to eyes, skin and respiratory system. Procedure Part A-Measuring reaction rate Using a measuring cylinder, pour 20 ml 2.0 M HCI into a 50 mL beaker. 2 Weigh approximately 20 g large marble chips into a 100 mL conical flask and loosely place a cotton wool plug in the neck of the flask. 3 Place the conical flask and the beaker of acid on the balance pan and tare the balance so that it reads zero. Carefully and quickly remove the cotton wool plug, add the acid to the flask, replace the beaker on the balance pan beside the flask, and replace the plug. Immediately start a stop-watch. 1 Copyright O Pearson Australia 2016 (a division of Pearson Australla Group Pty Ltd) ISBN 978 1 4886 1125 4 Page 1 Note the reading on the balance after 15 seconds, 30 seconds and at 30 second intervals thereafter. Continue for up to 10 minutes. 5 Draw up a table to record the mass loss (from the total starting mass) and the time, in minutes, from the start of the reaction. This could be done using a spreadsheet or graphing package. 6 Plot a graph of the mass loss against time. 4. tttn Part C-Effect of concentration Repeat the experiment as described in Part A, but this time use 20 mL 1.0 M HCI. Plot the graph of this data on the same set of axes as the first experiment.