ACTIVITY 5
PROPERTIES, PREPARATION and REACTIONS OF ALDEHYDES
MATERIALS
Copper (heated: CuO)
acetaldehyde
benzaldehyde
cinnamaldehyde
formaldehyde
methanol
ethyl alcohol
acid-dichromate
Fehling’s solution
Benedict’s solution
Tollen’s test
Schiff’s reagent
sodium bisulfate
NaOH
Pipette
Test tubes
PROCEDURE
A. PREPARATION
1. In formaldehyde experimentation, methanol was oxidized to produce formaldehyde. A heated
copper (glowing red) was dipped into 10 mL of methanol. The tube was sealed to prevent the
formaldehyde fumes from spreading. A small amount of water was added to dissolve the volatile
gas.
2. In the acetaldehyde experiment, ethanol was oxidized. Acid dichromate (K2Cr2O7 and H2SO4)
was mixed into 10 mL of ethyl alcohol.
B. PROPERTIES OF ALDEHYDES
The properties of aldehydes in formaldehyde, acetaldehyde, benzaldehyde, and cinnamaldehyde
were determined, as well as their solubility in water, density, flammability, and odor.
C. REACTIONS OF ALDEHYDES
1. OXIDATION
In the Oxidation experiment, the four aldehydes were oxidized by adding acid dichromate.
The products formed by their odor and color change were also determined.
2. REDUCING PROPERTIES
a) In Fehling's Test, 1 mL of freshly prepared Fehling's solution was mixed with 5 mL
of each of the test aldehydes.
b) In Benedict's Test, 1 mL of Benedict's solution was mixed with 5 mL of each of the
test aldehydes.
c) In Tollen's Test, 5 mL of freshly prepared Tollen's reagent was mixed with 10 mL of
each of the test aldehydes. The tube was soaked in water until a silver mirror formed.
d) In Schiff's Test, 1 mL of freshly prepared Schiff's reagent was mixed with 5 mL of
each of the test aldehydes.
e) In the reaction with Sodium Bisulfate, 1 mL of NaHSO4 solution was added to 5 mL
of each of the test aldehydes.
f) In the reaction with dilute alkalis, 1 mL of dilute NaOH was added to 5 mL of each
of the test aldehydes.