RP7-Measuring rate (Iodine clock)

• Equipment: Beaker, stopwatch, hydrogen peroxide, potassium iodide, sulfuric acid, sodium thiosulfate, deionised water.
• Set up: Add 25 cm^3 sulfuric acid, 20 cm^3 deionised water, 5 cm^3 sodium thiosulfate and 5 cm^3 potassium iodide solution to a beaker. In a separate beaker, measure 10 cm^3 of hydrogen peroxide solution.
• Method: Pour the hydrogen peroxide into the solution of sulfuric acid, water, sodium thiosulfate and potassium iodide and start the stopwatch. Stop the stopwatch when the mixture turns blue - black. Repeat with different concentrations of potassium iodide.
• Graph: Plot a graph of initial rate on the y axis and concentration on the x axis.
• Analysis: The shape of the graph can suggest the order of the potassium iodide.
• Alternate experiments: Use a colourimeter to get a more accurate measurement.