Test for the presence of
Glucose: add a few drops of Benedict’s solution to the sample and boil it.
Positive result: carrot colour
Chloride: add a few drops of silver nitrate solution to the sample.
Positive result: white colour
Starch: add a few drops of iodine solution to the sample.
Positive result: dark violet colour
The tested samples
Time (min)
0
TEST 1
5
TEST 2
Glucose
light blue
transparent
carrot
Chloride
blue transparent
white
Starch
brownish
orange
brownish
orange
10
TEST 3
15
TEST 4
20
TEST 5
carrot
yellow
brown
white
white
white
brownish
orange
brownish
orange
brownish
orange
25
TEST 6
25
(inside the
dialysing
tubing)
TEST 7
carrot
carrot
white
white
brownish
orange
dark violet
Chloride from TEST 2 to TEST 6 gradually became less and less transparent.
Conclusion and evaluation:
The word ’dialysis’ originates from a greek word, and it means separation. In this experiment different compounds were separated according to their size with the help of a dialysing tubing.
The tested compounds are different in their size of molecule/ion. Compared to each other, chloride is a small ion, glucose is a middle-sized molecule and starch is a large molecule.
The dialysing tubing let only the two smaller particles (chloride and glucose) through itself. The experiment showed that the particles oozed gradually, so the independent variable was time.
The samples taken at 0 minute (TEST 1) and at 25 minutes from the inside of the dialysing tubing (TEST 7) were negative tests. TEST 1 showed Benedict’s solution, silver nitrate solution and iodine solution when not reacting with glucose, chloride and starch. TEST 7 showed whether remained any glucose, chloride or starch inside the dialysing tubing.
Glucose, due to it small size could get through the dialysing tubing. In TEST 2, 3, 4, 5 and 6 the presence of glucose could be proved, although no gradual change could be seen. This might have been caused by error. TEST 7 showed that remained glucose in the tubing.
Chloride could get through the tubing as well as glucose. But unlike glucose, chloride from TEST 2 to TEST 6 showed less and less transparency, as a result of gradual quantity change. Not all the chloride particles oozed out of the tubing since TEST 7 resulted a white liquid.
Starch, being the largest of the 3 tested compounds, could not get through the tubing; TEST 2, 3, 4, 5 and 6 had the same results as TEST 1 had. TEST 7, resulting in dark violet colour testified it.
Dialysis has huge practical applications. The largest is in human health care. If someone has a kidney failure, urea will begin to accumulate in the blood. It can be removed by connecting the patient to a dialysis machine. Blood then circulates through the membrane and the urea (being a small molecule) is removed. Dialysis of blood is the biological function of kidney, that is why this organ is vital.
