Introduction 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. Variables Quantity Range Independent The concentration of glucose solutions 65%, 10%, 15%, 20%, 25%, 30% Dependent The time taken for the potassium permanganate solution to turn colourless, s Controlled Quantity Possible effect(s) on results 1. Volume of glucose solution in each boiling tube 0 cm3 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 10 cm3Different 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 2 cm3Different 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 5 cm3Solution with more quantity of sulphuric acid will decolourise faster as compared to solution with less acid 6. Size of beakers 3Different size of beaker might result in volume of solution being mistakenly put in, thus affecting the reading of this experiment
Materials and apparatus i) Materials Materials Quantity Molarity Glucose solutions 6 5%, 10%, 15%, 20%, 25%, 30% Unknown glucose concentration 3 (A, B, C) – Sulphuric acid 25 cm3 1M Potassium permanganate 25 cm3 – Table 1 : Materials used in the experiment (1) ii) Apparatus Apparatus Quantity Range (ml) Eye protection 1 – A timer 1 –
A glass rod 1 – A boiling tube and rack 1 – Beakers 3 0 – 50 Syringes 3 0 – 20 Labels 6 – Table 2 : Apparatus used in the experiment (2) Procedures (3) The three beakers are labelled; S – for sulphuric acid PP – for potassium permanganate G – for glucose The syringe is labelled in the same way. About 25 cm3 of sulphuric acid and potassium permanganate are added into the beakers. The correct syringe is used to place 10 cm3 of the first glucose solution into the boiling tube. cm3 of sulphuric acid is added. The solution is stirred with a stirring rod and stopped as soon as the pink colour disappears. The time and the glucose solution used is recorded. The syringe used for the glucose solution is rinsed. 10. The experiment is repeated using the other glucose solutions of known concentration. 11. It is then repeated for the solution of unknown concentration (A, B or C). 12. The results and the average results are recorded in a table. (1), (2), (3) Kolej Mara Banting – Students’ Handbook for Biology HL Year 1 Method to control variables
Variables Method to control Independent The concentration of glucose solutions Use different concentration of glucose solutions which is 5%, 10%, 15%, 20%, 25% and 30% Dependent The time taken for the potassium permanganate solution to turn colourless, s Observe and record the time taken for the potassium permanganate to turn colourless by using a stopwatch Controlled Volume of glucose solution in each boiling tube Volume of unknown glucose concentration; A, B and C Molarity of sulphuric acid Volume of potassium permanganate solution in each boiling tube
Volume of sulphuric acid in each boiling tube Size of beakers Fix the volume of glucose solution in each boiling tube which is 10 cm3 Fix the volume of unknown glucose concentration which is 10 cm3 Use the same molarity of sulphuric acid throughout the experiment which is 1M Fix the volume of potassium permanganate solution in each boiling tube which is 2 cm3 Fix the volume of sulphuric acid in each boiling tube which is 5 cm3 Use the same size of beaker which is 50 ml Data collection and processing i) Quantitative data Mean, x ? = ? x n
Standard deviation, S = v(? (x-(x)) ? )2 vn Trial Concentration of glucose solution, %Time taken for potassium permanganate solution to decolourise, s (±0. 01) Mean, s (±0. 01) ? x 5Standard deviation 1 2 3 4 5 5334330250380380 335 53 10200205170181150 181 22 151081161248993 106 15 207584867267 77 8 255545483439 44 8 304337402723 34 9
Table 3 : The time taken for potassium permanganate solution to decolourise in different concentration of glucose solution Mean Example of calculation 5% : 334 + 330 + 250 + 380 + 380 = 335 5 Standard deviation Example of calculation 5% : v((334-335)? +(330-335)? +(250-335)? +(380-335)? +(380-335)? ) v5 = 53 Trial Type of glucose solution Time taken for potassium permanganate solution to decolourise, s (±0. 01) Mean, s (±0. 01) ? x 5 Standard deviation 1 2 3 4 5
A – – – – – – – B 97. 0105. 0 91. 0 83. 0 80. 0 91. 2 10. 2 C 4. 0 3. 0 3. 0 3. 0 2. 5 3. 2 0. 4 Table 4 : The time taken for potassium permanganate solution to decolourise in unknown concentration of glucose solution Mean Example of calculation B : 97. 0 + 105. 0 + 91. 0 + 83. 0 + 80. 0 = 91. 2 5 Standard deviation Example of calculation B : v((97. 0-91. 2)^2+ (105. 0-91. 2)^2+ (91. 0-91. 2)? +(83. 0-91. 2)? + (80. 0-91. 2)? ) v5 = 10. 2 Rate of reaction, 1/t R = 1/t ? R = ? x R t Concentration / type of glucose Rate of reaction, s-1 (±0. 01) ? R, s-2 5% 0. 002985 4. 723 x 10-4 10% 0. 005525 6. 715 x 10-4 15% 0. 009434 0. 001 20% 0. 012987 0. 001 25% 0. 022727 0. 004 30% 0. 029412 0. 008 A – – B 0. 10965 0. 001 C 0. 312500 0. 039 Table 5 : The rate of reaction for each glucose concentration in this experiment Rate of reaction Example of calculation 5% : 1 335 = 0. 002985 Uncertainty for rate of reaction Example of calculation 5% : 53 x 0. 002985 335 = 4. 723 x 10-4 ii) Qualitative data The sulphuric acid has a pungent smell, which is a vinegary-like smell. The colour of the known concentration of glucose solution and sulphuric acid is colourless. Potassium permanganate solution is purple-pink in colour.
The colour of the potassium permanganate solution turns colourless when allowed to react with glucose solution. Higher concentration of glucose solution takes a shorter time to decolourise potassium permanganate. Discussion At 5% concentration of glucose solution, the mean time taken to decolourise the potassium permanganate is 335 seconds. This is the longest time taken compared to the other glucose solution. This is because the glucose solution is dilute at this concentration. From this experiment, we know that redox reaction is involved. Glucose undergo oxidation by releasing electrons to be accepted by manganate ions.
The presence of manganate ions causes the glucose solution to be purple-pink in colour. Manganate ions undergo reduction to form manganese ion, which is colourless in the solution. This means that less electrons are present in 5% glucose concentration and therefore, it takes a longer time to decolourise the potassium manganate solution. Sulphuric acid acts as a catalyst in this experiment to speed up the reaction. At 10% glucose concentration, the mean time taken is 181 seconds. It is slightly faster than the previous glucose solution. More electrons are present to react with manganate ions.
Next, the mean time taken to decolourise potassium manganate solution is 106 seconds for 15% glucose concentration. The time taken keep on decreasing, indicating that the following experiment is getting faster. The same reason applies; more electrons present means that more manganate ions can react to form manganese ions, which is colourless. At 20% concentration of glucose solution, the time taken is 77 seconds, which is faster than the previous concentration and at 25% concentration, it takes 44 seconds to completely deccolourise the potassium permanganate solution.
Finally, at 30% glucose concentration, which is the highest concentration in this experiment, the time taken is the shortest which is 34 seconds. More electrons are present in this solution to react with potassium manganate solution. Therefore, more manganate ions can be converted to manganese ions at a faster rate. For solution A, there is no reading available. The potassium permanganate solution did not turn colourless even after stirring for almost 10 minutes. The best reason to explain this is maybe there is no glucose at all in the solution.
Absence of glucose make it impossible for the solution to turn colourless. This is because no electrons are given off to react with manganate ion. The ion is not converted to manganese ion and the purple-pink colour remains. For solution B, which has a concentration of , the mean time taken is 91. 2 seconds and 3. 2 seconds are needed to decolourise potassium permanganate solution for solution C, which has a concentration of . The time taken is very short, meaning that this solution contains a very high concentration of glucose solution.
The solution is decolourised in less than five seconds. A lot of electrons are present to react with manganate ion to change into manganese ion. The purple-pink colour disappears very quickly to become colourless. Below is discussed the limitations and suggestions for this experiment. Conclusion The hypothesis is accepted. The higher the concentration of glucose solution, the shorter is the time taken to decolourise potassium permanganate. Higher concentration of glucose means more electrons are present to react with manganate ions.
More manganate ions are converted into manganese ions in a shorter time. Thus, the time taken is less. Evaluation Limitations Suggestions Presence of bubbles in the syringe. This will affect the volume of solution being usedWhen using the syringe to extract the solution, it is made sure that no bubbles are present. If there is, the step is repeated until no bubbles are seen inside the syringe Glucose solution being exposed already oxidized, affecting the reading of the experimentIt is best to use a freshly-prepared glucose solution to avoid using oxidized glucose.
Glucose stored in airtight container can also be used The degree of colourlessness of the solution is not the same for each glucose concentrationAfter one glucose concentration has been allowed to react with potassium permanganate, the sample is kept as a reference for the next glucose concentration References Kolej Mara Banting – Students’ Handbook for Biology HL Year 1 www. saps. org. uk/attachments/article
