Glucose is very important in our daily lives. It gives us energy to carry out all of our activities. Cells in our bodies need glucose to respire and in the process release the energy we need. Glucose is also a type of carbohydrate. It has a chemical formula of C6H12O6 and is a monosaccharide reducing sugar (Kolej Mara Banting – Students’ Handbook for Biology HL Year 1). It is the simplest form of carbohydrate. In this experiment, sulphuric acid, H2SO4 and potassium permanganate, KMnO4 is added into glucose with different concentration and the time taken for the purple pink colour of potassium permanganate solution to change to colourless is recorded. This is because glucose donates electrons to the permanganate ions, causing it to change colour (Kolej Mara Banting – Students’ Handbook for Biology HL Year 1).
MnO4- + 8H+ + 5e- ------> Mn2+ + 4H2O (Purple pink in (Colourless in solution) solution)
The manganate ion (MnO4-) is reduced to a colourless solution of manganese ion (Mn2+). As a result from this reaction, the glucose is oxidized (Kolej Mara Banting – Students’ Handbook for Biology HL Year 1). The time taken for the potassium permanganate to change colour from purple pink to colourless is directly related to the concentration of glucose present in solution (Kolej Mara Banting – Students’ Handbook for Biology HL Year 1).
Research question : How does the different concentration of glucose in solution affects the time taken by potassium permanganate to change colour from purple pink to colourless?
Hypothesis : The higher the concentration of glucose in a solution, the shorter the time taken by potassium permanganate solution to change colour from purple pink to colourless. This is because the more concentrated the glucose content in a solution, more electrons are present in the solution. This means that more manganate ions can receive the electrons compared to a less concentrated glucose content in a given period of time.
The concentration of glucose solutions
5%, 10%, 15%, 20%, 25%, 30% Dependent
The time taken for the potassium permanganate solution to turn colourless, s
Possible effect(s) on results 1. Volume of glucose solution in each boiling tube
Different volume of glucose means different electrons being given off to react with manganate ions, thus will affect the time taken recorded 2. Volume of unknown glucose concentration; A, B and C
Different volume of glucose means different electrons being given off to react with manganate ions, thus will affect the time taken recorded 3. Molarity of sulphuric acid
A more concentrated acid will speed up the reaction faster compared to a diluted one, thus affecting the time taken to decolourise potassium permanganate solution 4. Volume of potassium permanganate solution in each boiling tube
Different volume of potassium permanganate will affect the time taken for the solution to decolourise, where solution with extra volume of potassium permanganate taking a longer time compared to the others 5. Volume of sulphuric acid in each boiling tube
Solution with more quantity of sulphuric acid will decolourise faster as compared to solution with less acid 6. Size of beakers
Different size of beaker might result in volume of solution being mistakenly put in, thus affecting the reading of this experiment
Materials and apparatus
Molarity Glucose solutions
5%, 10%, 15%, 20%, 25%, 30%...
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