Measuring rates of reaction by production of gas It is important in this practical to use appropriate apparatus to make and record a range of measurements accurately, including mass, time, temperature and volume. This practical includes the safe use of apparatus and monitoring chemical changes. This outlines one way to carry out the practical. Eye protection must be worn. Aims To investigate the effect of changing the conditions on the rate of a reaction. Calcium carbonate reacts with dilute hydrochloric acid: calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide CaCO 3 (s) + 2HCl(aq) → CaCl 2 (aq) + H 2 O(l) + CO 2 (g) The volume of carbon dioxide gas produced can be measured using a gas syringe. Part 1 Changing the concentration of acid Method Support a gas syringe with a stand, boss and clamp. Using a measuring cylinder, add 50 cm 3 of dilute hydrochloric acid to a conical flask. Add 0.4 g of calcium carbonate to the flask. Immediately connect the gas syringe and start a stop clock. Record the volume of gas produced every 10 seconds. When the reaction is complete, clean the apparatus. Repeat steps 1 to 5 with different concentrations of hydrochloric acid. Measuring gas using a syringe and conical flask Results Record the results in a table.
Time (s) Volume of gas produced (cm 3 ) 0 0 10 20 Analysis For each concentration of hydrochloric acid, plot a graph to show:
volume of gas (cm 3 ) on the vertical axis time (s) on the horizontal axis draw a curve of best fit For each concentration of acid, calculate the mean rate of reaction until the reaction stopped:
Describe the effect of increasing the concentration of acid on the mean rate of reaction. Use your graphs and calculations in step 2 to help you. Evaluation Question Describe how you can tell that the reaction is complete. Reveal answer No more gas is produced, and the line on the graph becomes horizontal. Part 2 - Changing the temperature Carry out the experiment described above, but: keep the concentration of acid the same warm the acid to different temperatures using a hot water bath or a Bunsen burner, tripod and gauze measure and record the temperature of the acid describe the effect of increasing the temperature on the mean rate of reaction Part 3 - Changing the surface area to volume ratio Carry out the experiment described above, but: keep the temperature and concentration of acid the same use different sized pieces of calcium carbonate, including a powder describe the effect of increasing the surface area to volume ratio on the mean rate of reaction Hazards, risks and precautions
Hazard Possible harm Possible precaution Hot hydrochloric acid Causes skin and eye irritation. Burns to the skin. Wear gloves and eye protection. Do not heat above 60°C. Fizzing in the reaction mixture Spray or foam escaping, which may damage skin and eyes. Use a large conical flask so there is plenty of space inside. Do not look over the top when adding the calcium carbonate.