Data:
1st
2nd
Table of experimental average saturation point
Data analysis:
The experimental result follows the general trend of solubility that glucose being the most soluble, followed by galactose and lactose being the least soluble in water.
However, there is still an obvious different between the experimental and theoretical value.
The error may due to :
1) The experiment is not carry out exactly at room temperature (25 c) and the temperature is not keep constant throughout the experiment.
2) There are solution “stick” onto the surface of magnetic stirrer.
Precaution and improvement of experiment:
- Start the magnetic stirrer slowly to avoid splash out of solution.
- Keep a rough record of approximate quantitives added from time to time as it is useful to guide for future addition in the second times.
- Allow more time for carbohydrates to dissolve because when approaching the saturation point, the carbohydrates dissolve quite slow.
- Avoid and unnecessary transfer of solution using container to reduce the lost of substances.
Result :
The saturation point of glucose is 639.1 mg/ml, Galactose is 189.4 mg/ml and that of lactose is 40.4 mg/ml.
Discussion :
All sugars are soluble in water because of the present of hydroxyl group, forming hydrogen bond with water molecules. The different in solubility of glucose, galactose and lactose can be attributes to the different in structure of them.
Glucose and galactose are both monosaccharides (C6H12O6) but the solubility of glucose is higher than galactose because in glucose the hydroxyl group bond to the 4th carbon is pointing downward while that of galactose is pointing upward the same direction with the third hydroxyl group.
This makes intramolecular hydrogen bond is likely to be formed in galactose, rather than forming intermolecular hydrogen bond with water molecules.
Lactose is a disaccharides, formed by joining glucose and galactose by a glycosidic linkage, which has a large molecular size. So, lactose has a lower solubility than glucose and galactose.
The differences of solubility between glucose, galactose and lactose can be related to their use in humans.
Glucose, which has higher solubility in water, can act as an immediately source of energy. Glucose molecules can easily pass through the cell membranes into cell also transported easily within the cell. Take respiration of cell as an example, the process is start with glycolysis. The glucose move to cytosol and the molecules are split into two pyruvates, to prepare for the breakdown to provide energy.
The high solubility of glucose, make it easy to transport in the bloodstream to their destination. For example, glucose can transport to brain and directly utilized as an energy sources by brain cell.
Lactose has a low solubility in water. Human breast milk contains high content of lactose. After milk has been eaten, as lactose has low solubility, the lactose can stay in the ileum for a longer time rather than drift away like liquid quickly. This increase the time for lactase to break down lactose into glucose and galactose, hence have a more effective absorption.
Moreover, the lactose’s low solubility makes lactose absorption slower. So lactose is safe to consume by diabetes human, since lactose won’t cause a fast increase in blood glucose level.