18 RATE OF REACTION a SIZE OF PARTICLES AND RATE OF REACTION Marble chips can be broken up with a hammer and graded into 3 or 4 sizes a coarse powder b pieces about half the size of a rice grain c pieces as large as rice grains and d the original lumps of marble chips Place four 100 X 16 mm test tubes in a stand Weigh approximately 2 g of each grade size of marble chips and put the four grades separately into each of the four tubes Obtain four balloons and blow them up several times to stretch them Put 5 mL of bench hydrochloric acid into each of the four balloons and slip the mouth of the balloon over the top of the tube without letting any acid into the tube When each balloon is in place tip the acid into each testtube at the same time and observe which balloon is the fastest and the slowest to be blown up The smallest should give the carbon dioxide in the shortest time Instead of using marble chips you can use granulated zinc Do not use metals in powder form because the reaction may be too vigorous and even cause an explosion Be careful This reaction produces hydrogen gas Instead of collecting the gas in a balloon or plastic bag a more accurate method would be to collect the gas in a burette inverted over water and compare the volume of gas given off in unit time for each grade of marble chips Another accurate method is to stand a conical flask containing the marble chips and acid on a balance and record the loss in mass every half minute Carbon dioxide is a heavy gas and most balances will enable the loss in mass to be found as the gas escapes