Which factors affect reaction rate? 3rd April 2009 content from various sources, compiled by H Graham BSc PGCE

Thiosulphate.jpg sodium thiosulphate Na 2 S 2 O jpg hydrochloric acid HCl

Na 2 S 2 O 3 HCl S SO 2 NaCl H2OH2O Use these to build the chemical equation

253 Safety There are a lot of safety issues we must abide by in this experiment also. We must remember that the substances which we use in this experiment can be very harmful if used the wrong way. When we do this experiment, it may be necessary to wear safety goggles, as things are very unpredictable, and even though it is very unlikely that the solution would come out of the beaker during the experiment, one must still be cautious of spills. We must make sure that coats and bags are all out of the way while doing the experiment. Ties and hair should be tucked out of the way, so they do not make contact with any of the chemicals. It would also be preferable to wear a scientific apron, however this is not essential. We should also try our best not to spill any chemicals, and we must not eat or drink in the lab while dealing with these harmful chemicals, as they can get on to our hands.

Procedure Firstly, we drew a black cross on a white piece of paper. Then, we put 5 cm 3 of hydrochloric acid in a beaker, and then put the beaker on the black cross on the paper. We then added 50 cm 3 of Sodium Thiosulphate to the hydrochloric acid, and at this time we do not need to add any water.. Immediately, we started the stopwatch. We then waited for the black cross to be completely hidden by the mixture. When this happened we stopped the stopwatch. By this time the mixture was completely cloudy. Then we recorded what the time was. We then emptied out the contents of the beaker, cleaned it out and dried it out. Next, we added 45 cm 3 of Sodium Thiosulphate; we kept the HCl acid constantly at 5 cm 3. Now, because we have to keep the volume the same for it to be a fair test, we added 5 cm 3 of water. (We had to add the Sodium Thiosulphate and the water at the same time for this to be a fair test also). We then recorded the time for the cross to become completely obscured. We repeated this many times, adding different amounts of Sodium Thiosulphate and water each time, and recording the time taken each time. X

volume thiosulphate time (seconds) volume acid temperature concentration RESULTS? 253

plot results as line graph? 253

swf How could this investigation be developed? Design your own procedure