Transcript Estimating glucose concentration in solution

Estimating glucose
concentration in solution
Introduction
The purple pink solution of potassium permanganate
(MnO4 -) is reduced by glucose to a colourless solution of
manganese ions (Mn2+).
MnO4-
+
Purple pink
in solution
8H+
+ 5e- Mn2+ + 4H2O
colourless
in solution
The time taken for the loss of colour from a standardised
solution of permanganate is directly related to the
concentration of glucose present in solution.
Aims
• To determine the effect of increasing
glucose concentration on the rate of
reaction.
• To estimate the concentrations of three
glucose solutions of unknown
concentration.
Materials
Materials required by each group:
Eye protection
8 boiling tubes
3 syringes
labels/marker pens
timer(s)
boiling tube rack
glass rod
Glucose solutions (2, 4, 6, 8 and 10%)
3 glucose solutions of unknown concentration (A,B and C)
Sulphuric Acid ( 1 mol dm-3)
Potassium permanganate ( 0.4 g dm-3)
Procedure
1. Label your syringes (‘G’ for glucose, ‘P’ for
potassium permanganate and ‘S’ for Sulphuric
acid).
2. Label your boiling tubes with the different
glucose concentrations to be used.
3. Use the 10 cm3 syringe to place 10 cm3 of the
correct glucose solution into each boiling tube.
Start with the lowest concentration and work up.
Procedure (2)
4. Use the correct syringes to add 5 cm3 of
sulphuric acid to the 2% glucose in the
boiling tube.
5. Add 2 cm3 of potassium permanganate to the
same tube and start the clock.
6. Stir with a stirring rod and stop the clock as
soon as the pink colour disappears. (Hold
boiling tube up against white paper.)
Procedure (3)
7. Record the time taken.
8. Repeat steps 4 – 8 for each glucose solution of
known concentration, working from lowest to
highest concentration.
9. Repeat steps 3 – 8 for the glucose solutions of
unknown concentration (A, B and C).
10.
Record your own results and, if possible,
class average results in a table.
Glucose
concentration
(%)
2
4
6
8
10
Time to turn KMnO4 colourless
(seconds)
Group 1 Group 2 Group 3 Average
Results
Glucose
concentration
(%)
A
B
C
Time taken to turn KMnO4 colourless
(seconds)
Group 1 Group 2 Group 3 Average
Results
11. Plot a standard curve of your own and the class
average results on graph paper. Use the graphs to
estimate the concentrations of the unknown solutions.
Show your interpolations on the graph.
12. Calculate 1/time using class average results and draw
a graph of rate of reaction.
Results – plot graphs
Time
taken to
become
colourless
(s)
1/T
(s-1)
Glucose
concentration %
Glucose
concentration %
Conclusion
• Are there any trends in your results?
• If so, describe the relationship between glucose
concentration and the time taken to turn potassium
permanganate colourless/the rate of reaction.
• What are the estimated concentrations of your ‘unknown’
solutions?
Evaluation
• Ask your teacher for the concentrations of solutions A,B
and C and compare the actual concentrations with your
estimated concentrations.
• Compare your results with the class average results.
• Did your experiment work well?
• What variables did you control effectively?
• What were the sources of error in your experiment?
• How could you improve on the design of your experiment
and minimise the effects of errors?