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Aims
Aims
To use a clock reaction to find the order of reaction with respect to iodide ions
To use a clock reaction to find the order of reaction with respect to iodide ions
To use a clock reaction to find the order of reaction with respect to peroxodisulfate ions
To use a clock reaction to find the order of reaction with respect to peroxodisulfate ions
A. Report & Analyse of Results
A. Report & Analyse of Results
1. Record your results.
2. Calculate the concentration of iodide ions in each of the 25.0 cm3 solutions for experiments (a)–(e). Write these values in Table 2.
3. Use the times recorded in each experiment to work out the rates for these experiments. Write these values in Table 2.
4. Plot a graph of rate against concentration. Deduce the order of the reaction with respect to iodide ions.
5. Using the data from the first experiment (a) and the data from (f)–(i), work out the concentration of the peroxodisulfate ion in 25.0 cm3 of solution. Write these values in Table 2.
6. Work out the rate for each of these concentrations. Write these values in Table 2.
7. Plot a graph of rate against concentration. Deduce the order of the reaction with respect to peroxodisulfate ions.
Table 2
Things to consider CPAC 5a
Things to consider CPAC 5a
CPAC 5a - uses appropriate software and/or tools to process data, carry out research and report findings
· Carry out suitable research and writes up in own words citing relevant information, facts and figures within the text as necessary.
Things to consider CPAC 5b
Things to consider CPAC 5b
CPAC 5b – Sources of information are cited demonstrating that research has taken place, supporting planning and conclusions
· Clearly identifies any material that is a direct quote as such.
· Use research to explain & support any conclusions drawn
· Compile a bibliography of texts from which material has been sourced in such a way that the reader may retrieve the information easily.
B. Evaluate your report by answering the questions
B. Evaluate your report by answering the questions
1. Identify the main sources of uncertainty in the procedure used and the measurements recorded in this experiment. Calculate the percentage uncertainty for any measurements taken.
2. Suggest ways of minimising these uncertainties.
3. What is the overall rate equation for this reaction?
The equation for the reaction is:
S2O8 2− + 2I− → 2SO4 2− + I2
4. A suggested mechanism for the reaction is:
step 1 I − + S2O8 2− → (S2O8I)3−
step 2 (S2O8I)3− + I − → 2SO4 2− + I2
Which of these steps is the rate-determining step? Use the rate equation to justify your answer.
Math you will find useful
Math you will find useful
Translate information between graphical, numerical and algebraic forms.
Plot two variables from experimental or other data.
Learning Tip
Learning Tip
The initial rate is the instantaneous rate at the start of a reaction when the time, t is zero (t = 0). The initial rate can be found by measuring the gradient of a tangent drawn at t = 0 on a concentration−time graph.
A clock reaction is a more convenient way of obtaining the initial rate of a reaction by taking a single measurement. The time, t, is measured from the start of an experiment for a visual change to be observed. This often involves a colour change or the formation of a precipitate.
If there is no significant change in rate during this time, it can be assumed that the average rate of reaction will be the same as the initial rate. The initial rate is then proportional to 1 / t .
C. Evaluate your Practical by Completing the Form- so you know where you should aim to make improvements in future
C. Evaluate your Practical by Completing the Form- so you know where you should aim to make improvements in future
Required Resources
Required Resources
Core Practical 13b Student Evaluation.docxCore Parctical 13b - Student Sheet.docxConsult CLEAPSS Hazcards® 54, 85A,95A,98A. Perform a risk assessment using up-to-date information before this practical is carried out
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