3.Shake each test tube gently to mix the solutions,
and place them in a hot water bath for 5–10 min.
Note any change in the colour of the solutions.Part B: Testing for the Presence of
Polysaccharides
1.To one test tube, add 5 mL of starch and 5 mL of
cold, distilled water.
2.To another test tube, add 10 mL of cold, distilled
water.
3.Add three drops of Lugol solution to each test tube.
Note any changes in the colour of the solutions.Part C: Hydrolysis of Disaccharides
1.Add 3 mL 1% solution of sucrose to each of two
test tubes, labelled 1 and 2.
2.Add 3 mL of distilled water to a third test tube,
labelled 3.
3.Add five drops of Benedict’s solution to each test
tube. Note any changes in the colour of the
solutions in your data chart.
4.Repeat steps 1 and 2 using clean test tubes.
5.Add three drops of hydrochloric acid (HCl) to test
tubes 1 and 3.
6.Heat the test tubes in hot water for about 3 min.
7.Add five drops of Benedict’s solution to each test
tube. Note any changes in the colour of the solutions.Part D: Hydrolysis of Polysaccharides
1.To one test tube, add 5 mL of potato starch and
5 mL of water. Shake gently.
2.Now add 3 mL of concentrated hydrochloric acid to
this test tube, and stir the solution.3.To a second test tube, add 5 mL of potato starch to
8 mL of water. Shake gently.
4.To a third test tube, add 13 mL of distilled water.
5.Place the three test tubes in a hot water bath.
6.Using a clean dropper each time (or one rinsed with
distilled water), remove five drops of solution from
each test tube. Place each sample in a separate
well in the spot plate.
7.Immediately add one drop of Lugol solution to each
sample. Note any changes in colour.
8.Repeat steps 6 to 9 every minute, until no further
colour changes are observed for three consecutive
tests.Post-lab Questions
1.What do these laboratory procedures indicate about
the composition of polysaccharide molecules such
as starch?
2.How does the presence of HCl change the structure
of polysaccharide molecules?
3.What do the colour changes observed in the Lugol
and Benedict’s solution indicate about the
concentrations of the various substances tested?Conclude and Apply
4.What environmental factors cause hydrolysis? What
evidence did you use to determine this?
5.Find the structural formula for starch. Use diagrams
to show how hydrolysis changed this molecule.
6.Identify other molecules that could react in a similar
way with these environmental conditions.Chapter 1 The Chemistry of Life • MHR 25The terms “oxidation” and “reduction” are
applied to many reactions involving ions whether
or not oxygen is involved. For instance, in the
reaction Na+Cl→NaCl, chlorine is reduced
(gains an electron to form Cl−) and sodium is
oxidized (Na loses an electron to form Na+).
Because reduction and oxidation are both involved
in the process, the entire reaction is called a redox
reaction. Figure 1.16 is a generalized schematic
representation of a redox reaction.
Figure 1.16Oxidation is the loss of one or more electrons.
Reduction is the gain of one or more electrons.oxidation reduction