In this Experiment, we will investigate the effect of varying concentrations of Potassium Iodide on its reaction with Hydrogen peroxide, which will stay at a fixed concentration. This reaction may also be known as the ‘Iodine Clock Reaction. ‘ The rate of the reaction will be measured by timing the reaction between Hydrogen Peroxide, Potassium iodide, and Sodium Thiosulphate. Sodium Thiosulphate is used as a delaying mechanism as the reaction between the two main reactants is too rapid o measure.
The Sodium Thiosulphate will react with the Iodine ions (the product) first and when the all the Sodium Thiosulphate has reacted, then the remaining Iodine ions will form a blue-black solution because of the addition of Starch into the solution. The Ionic Equation for this reaction is: (aq. ) + 2S2032- (aq. ) 31- (aq. )+S4062- (aq. ) (aq. ) + 2H20 (l. ) H202 (aq. )+ 31- (aq. )+ 2H+ A stopwatch will be used to measure the time taken for the blue-black color of the solution to completely cover the “X” marked on the tile the conical flask is standing
Variables: Independent Variable: Concentration. (The changing concentrations of Potassium Iodide. ) Dependent Variable: Rate of the Reaction. (The amount of time taken for the blue-black starch complex to cover the ‘X’ marked on the tile. ) Control Variables: i. Concentration of the Hydrogen Peroxide and Sodium Thiosulphate. it. pH of the Nitric Acid used to acidify the Hydrogen Peroxide Solution. iii. Volume of Potassium Iodide Solution, Hydrogen Peroxide Solution, Nitric Acid, Starch and Sodium is conducted. v. The apparatus used should remain the same so as to avoid minor rrors.
Hypothesis: My hypothesis is that the rate of the reaction will increase as concentration increases and will then steady and stay the same. This is because the collision theory states that if the number of particles of one of the reactants increases, then the chance of collision between the two reactants is higher, thus increasing the rate of the reaction. The Potassium Iodide particles will increase and the frequency of their collisions with Hydrogen Peroxide particles will also increase, causing them to react quicker.
I ypothesize that as I increase the concentration of the Potassium Iodide Solution, the rate at which the blue-black starch complex covers the ‘X’ marking on the tile, will also increase until a point where the rate will remain the same due to all the particles having already finished reacting. 1 The rate of the reaction is directly proportional to the concentration of a reactant. Concentration of Potassium Iodide 0 Time taken for ‘X’ to get covered. Apparatus: Hydrogen Peroxide (H202) Solution (1. 500 ?± 0. 001)g of Potassium Iodide (KI) Powder Sodium Thiosulphate (NaS203) Solution
Dilute Nitric Acid (HN03) Solution Starch Solution Tile marked ‘X’ Conical Flask Digital Stopwatch (?±O. 01seconds) Measuring Cylinder (?±O. 5cm3) Electronic Balance (?±O. OOI g) Distilled Water Procedure: 1 . Prepare Potassium Iodide (KI) solution by dissolving (1. 500 ?± 0. 001) g of Potassium Iodide Powder into (50. 0 ?± 0. 5) cm3 of Distilled Water. 2. Make 5 different (10. 0 ?± 0. 5) cm3 solutions of different concentrations of KI. (?±0. 5) crn3 Volume of Distilled Water Total Volume of KI Solution (?±1. 0) cm3 Concentration of KI Solution (MOI. KI / drn3) . 8. 0 10. 0 4. 0 6. 0 10. 0 (Blank) 0. 0 3. Acidify the Hydrogen Peroxide by adding 10 drops of Dilute Nitric Acid to it. 4. Pour 5cm3 of the acidified Hydrogen Peroxide into 5 different conical flasks/beakers. Mark this Flask ‘A’. 5. Add 10cm3 of Starch and lcm3 of Sodium Thiosulphate to a conical flask/beaker containing one of the prepared concentrations of KI. Mark this Flask ‘B’. 6. Pour all the contents of Flask ‘A’ into Flask ‘B’, which is standing on a tile marked with a large ‘X’. 7. Start the stopwatch immediately after adding the contents of ‘A’ nto ‘B’. . Stop the stopwatch as soon as the ‘X’ has completely disappeared from view. 9. Record all readings and observations. 10. Repeat this procedure once again to ensure accuracy. 1 1 . Repeat this same procedure with all the other potassium iodide concentrations too. 12. Record all the readings and observations. 13. The record table should look something like this: Concentration of KI (mol/dm3) 2. 3. 4. 5. 14. Find the average of all the readings and create a Concentration of Potassium Iodide (concentration/cm3) x Rate of Reaction (time/seconds) graph.