method

• 1. add about 10cm3 of 1 moldm-3 HCl (or 0.5moldm-3 H2SO4) to the acid tube. Place this tube into the correct hole in the plastic container (the one without the cross)
• 2. use a measuring cylinder to add 10cm3 of 0.05moldm-3 sodium thiosulphate solution to the second tube. Place this tube into the correct hole in the plastic container (one with the cross) and carefully place a thermometer in this tube
• 3. note the temperature and then add 1cm3 of the acid to the thiosulphate solution and start timing
• 4. look down through the vial from above and record the time for the cross to disappear from view
• 5. pour the cloudy contents of the vial into 100cm3 Na2CO3 solution + few drops of phenolphthalein (the 'stop bath')
• 6. add water from a very hot water tap / kettle to the plastic container. The water should be no hotter than 55°C. Add cold water if necessary
• 7. measure another 10cm3 of 0.05 moldm-3 sodium thiosulfate solution into a clean tube. Insert this tube into the correct hole in the plastic container (cross)
• 8. allow the vial time to adjust to the new temperature
• 9. repeat steps 3 to 5 above
• 10. repeat to obtain results for at least 5 different temperatures in total