Section 1 Harcourt-Essen Reaction
A2 Chemistry Coursework
Section 1
Aims:
I aim to find out the order of reaction with respect to [H2O2] and [2I-].
I aim to find out the activation enthalpy of the reaction by finding the rate of reaction at different temperatures using the Arrhenius Equation.
The experiment will go as follows:
Into a conical flask put 15cm3 of distilled water and add 2cm3 of [X]moldm-3 potassium iodide (KI) solution and 1cm3 of 2moldm-3 sulphuric acid. Then add to this 2.5cm3 of 5vol (0.42moldm-3) hydrogen peroxide (H2O2). For the second part of my investigation, the KI solution will remain a constant 0.3moldm-3 and the H2O2 solution will vary.
H2O2 + 2I- + 2H+ -> 2H2O + I2
Methods to find the rate:
1 - Use a colorimeter to monitor the change in absorbance as the reaction progresses, showing how the concentration of Iodine changes with time and how varying concentrations of KI and H2O2 solutions affects the rate of reaction.
2 - Use an iodine clock: add 2cm3 of 0.1moldm-3 sodium thiosulphate (Na2S2O3) and 1cm3 of 1% starch solution at the start of the reaction. The added sodium thiosulphate reacts with the iodine as it's formed:
I2 + 2Na2S2O3 -> 2NaI + Na2S4O6
When the sodium thiosulphate is all used up the iodine remains in solution and reacts with the starch indicator to make the blue colour.
I will vary the temperature and time how long it takes for a colour change of blue to appear, and from this calculate the activation enthalpy of the Harcourt-Essen reaction. I will keep the temperature's constant with the use of water baths and fresh ice. The KI wil be kept at a constant 0.3moldm-3 and the H2O2 will be kept at a constant 5 vol.
Concentrations to be used:
0.3, 0.25, 0.2, 0.15, 0.1 and 0.05moldm-3 potassium iodide - from solid KI (constant 0.3moldm-3 for varying H2O2)
6, 5, 4, 3, 2 and 1vol hydrogen peroxide - from 20vol (1.68moldm-3) H2O2 via dilution (constant 5vol for varying KI)
Chemical Ideas:
Harcourt-Essen reaction:
The iodine clock reaction (also known
Section 1
Aims:
I aim to find out the order of reaction with respect to [H2O2] and [2I-].
I aim to find out the activation enthalpy of the reaction by finding the rate of reaction at different temperatures using the Arrhenius Equation.
The experiment will go as follows:
Into a conical flask put 15cm3 of distilled water and add 2cm3 of [X]moldm-3 potassium iodide (KI) solution and 1cm3 of 2moldm-3 sulphuric acid. Then add to this 2.5cm3 of 5vol (0.42moldm-3) hydrogen peroxide (H2O2). For the second part of my investigation, the KI solution will remain a constant 0.3moldm-3 and the H2O2 solution will vary.
H2O2 + 2I- + 2H+ -> 2H2O + I2
Methods to find the rate:
1 - Use a colorimeter to monitor the change in absorbance as the reaction progresses, showing how the concentration of Iodine changes with time and how varying concentrations of KI and H2O2 solutions affects the rate of reaction.
2 - Use an iodine clock: add 2cm3 of 0.1moldm-3 sodium thiosulphate (Na2S2O3) and 1cm3 of 1% starch solution at the start of the reaction. The added sodium thiosulphate reacts with the iodine as it's formed:
I2 + 2Na2S2O3 -> 2NaI + Na2S4O6
When the sodium thiosulphate is all used up the iodine remains in solution and reacts with the starch indicator to make the blue colour.
I will vary the temperature and time how long it takes for a colour change of blue to appear, and from this calculate the activation enthalpy of the Harcourt-Essen reaction. I will keep the temperature's constant with the use of water baths and fresh ice. The KI wil be kept at a constant 0.3moldm-3 and the H2O2 will be kept at a constant 5 vol.
Concentrations to be used:
0.3, 0.25, 0.2, 0.15, 0.1 and 0.05moldm-3 potassium iodide - from solid KI (constant 0.3moldm-3 for varying H2O2)
6, 5, 4, 3, 2 and 1vol hydrogen peroxide - from 20vol (1.68moldm-3) H2O2 via dilution (constant 5vol for varying KI)
Chemical Ideas:
Harcourt-Essen reaction:
The iodine clock reaction (also known
References: Reference 1: Harcourt-Essen reaction (last accessed 10/11/2013) http://en.wikipedia.org/wiki/Iodine_clock_reaction Reference 2: Iodine clock reaction (last accessed 11/11/2013) http://openstudy.com/study#/updates/4fa0c4a0e4b029e9dc31cdb1 Reference 3: "Salter 's Advanced Chemistry: Chemical Ideas"; 3rd Ed; Heinemann Educational Publishers: 2008; pg. 157 "Using ultraviolet and visible spectra" Reference 4: Colorimeter (last accessed 15/11/2013)