Factors Affecting Rate of a Reaction, Chemistry Design Lab

Topics: Hydrogen peroxide, Sodium, Chemical reaction Pages: 5 (811 words) Published: December 9, 2013
Chemistry Lab Report
Factors affecting Rates of a Reaction (Kinetics)

Research Question:
Does the concentration of Potassium Iodide (KI) affect the rate of its reaction with hydrogen peroxide (H2O2) (of a fixed concentration)?

There are several factors that affect the rate of a reaction. Some of them being Pressure (if the reactants are Gases), Temperature, Presence of a Catalyst, Surface Area of the reactant, and Concentration. According to the Collision Theory, during a reaction, particles collide with each other and react if the geometry of the collision is correct. 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 to measure. The Sodium Thiosulphate will react with the Iodine [III] 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.) + 2S2O32- (aq.)  3I- (aq.) + S4O62- (aq.)

H2O2 (aq.) + 3I- (aq.) + 2H+  (aq.) + 2H2O (l.)

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 on.

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. ii. 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 Thiosulphate used. iv. The temperature of the atmosphere each time the experiment is conducted. v. The apparatus used should remain the same so as to avoid minor errors.

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 hypothesize 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  Time taken for ‘X’ to get covered.

Hydrogen Peroxide (H2O2) Solution
(1.500 ± 0.001)g of Potassium Iodide (KI) Powder
Sodium Thiosulphate (NaS2O3) Solution
Dilute Nitric Acid (HNO3) Solution
Starch Solution
Tile marked ‘X’
Conical Flask
Digital Stopwatch (±0.01seconds)
Measuring Cylinder (±0.5cm3)
Electronic Balance (±0.001g)
Distilled Water


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.

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