Verneri Anttila, 1-IB,

18.10. 1997

Chemistry practical 2:

The chemical properties of ethanol

Aim:To study the properties of ethanol, a typical primary alcohol

Methods:

Part 1) Mild oxidation

In a pear-shaped flask, we mixed 10 cm3 of 1 M sulphuric acid (H2SO4 (aq)) with 3.00 grams of sodium dichromate(VI), a yellow solid, and 3 anti-bumping gran- ules. We swirled the flask until the sodium dichromate had dissolved into the acid. After that, we slowly added 5 cm3 of ethanol while swirling the flask to mix the solution. Then, we heated the solution gently in the apparatus shown below until about 5 cm3 of distillate had formed. The solution started boiling after 1 min 26 seconds, at approximately 35 degrees. We stopped heating after 4½ minutes, when the solution was in 85 degrees Celsius. The product was tested by

A) a volatility test: we smelled at first the distillate and then ethanol and compared the smells

B) Fehling’s solution test: we transferred about 1 cm3 of the distillate to a test- tube.Then 1 cm3 of both Fehling’s solution 1 and solution 2 were added, and the mixture gently boiled.

C) silver mirror test: we poured about 5 cm3 of silver nitrate solution into a boiling-tube and added one drop of sodium hydroxide solution to it, resulting a dark, cloudy mixture. Then, aqueous ammonia(NH4) was added until the precipitate disappeared. Then,2-3 drops of the distillate was added, and the tube warmed in a beaker containing hot water.

(image)

Part 2) Further oxidation

In a pear-shaped flask, we mixed 10 cm3 of 1 M sulphuric acid (H2SO4 (aq)) with3.00 grams of sodium dichromate(VI), a yellow solid, and 3 anti-bumping granules. We swirled the flask until the sodium dichromate had dissolved into the acid. Then 2 cm3 of concentrated sulphuric acid (18 M) was added into the solution, and the flask was kept under running cold water to compensate the heat which resulted of the addition of the concentrated sulphuric acid. The solution was inserted to the boiling/reflux apparatus shown below, and 1 cm3 of ethanol was carefully added. The solution was then boiled gently for 20 minutes. Then, about 2 cm3 of solution was distilled with the same apparatus as was used in part 1. The product was then (A) tested by smelling, (B) pH measured with moistened univer- sal indicator paper, and (C), a few drops were added to 1 g of sodium carbonate (Na2CO3 (s)).

(image)

Part 3) Tri-iodo methane reaction

In a testtube, we mixed 5 drops of ethanol with 1 cm3 of iodine solution. Sodium hydroxide (NaOH (aq)) was then added drop by drop until the brown color dis- appeared. The testtube was then warmed in a beaker containing hot water.

Part 4) Reaction with sodium

(Done by the teacher) Roughly 3 mm3 of pure sodium was dropped to a testtube containing 1 cm3 of ethanol. A lit match was then taken to the mouth of the test- tube.

Materials & Apparatus:

-20 cm3 of 1 M sulphuric acid

-3 cm3 of 18 M concentrated sulphuric acid

-6.0 g of sodium dichromate (VI)

-1 cm3 of glacial ethanoic acid

-10 cm3 of ethanol

-1 cm3 of iodine solution

-1 g of sodium carbonate

-some sodium carbonate solution

-some sodium hydroxide

-approx. 3 mm of solid sodium

-6 anti-bumping granules

-1 cm3 of Fehling’s solution 1

-1 cm3 of Fehling’s solution 2

-5 cm3 of silver nitrate solution

-1 thermometer

-1 pcs of universal indicator paper

-1 pcs of heating equipment(one bunsen lamp, one wire screen and one tripod)

-1 pcs of distillation equipment(one pear-shaped boiling flask, one condenser, one 100 ml erlenmeyer flask, two rubber tubes, one receiver adaptor, one screw-cap adaptor)

Results:

Part 1:

A) o

Na2Cr2O7(aq) + 4 H2SO4 + 3 CH3CH2OH(l) 

Cr2(SO4)3 (aq) + 3 CH3CHO + 7 H2O(l) + Na2SO4

The distillate smelled considerably different from the ethanol. In fact, it had a fruit-life smell, more accurately, the smell of pear, which would suggest the presence of an ester.

B) Cu2+ + 2 e-  Cu(0)

When the mixture containing ethanol and Fehling’s solutions 1 and 2 were heated, no changes were evident. The mixture was burned up after 40 seconds. When the mixture containing the distillate and the Fehling solutions was similarily heated, changes were clearly evident.

Time (seconds)Color of the mixture

0whole mixture clear blue

20whole mixture turned green

50surface turned yellow, rest is green

59the sprays from the mixture turned into a rust color

113red sprays, liquid turned dark blue

167black(coal, burned) bottom,yellow/red liquid

C)AgNO3 + NaOH AgOH + HNO3

AgOH + NH4 Ag+ + NH3+ + H20

distillate:CH3CH2CHO + Ag+ + O2  CH3CH2COOH + Ag (s)

ethanol:CH3CH2OH + Ag+ no reaction

With the distillate, a mirror surface formed after 2 minutes of heating. With alcohol, no surface had formed after 6½ minutes of heating. At this point, we poured a few cm3 ’s of the distillate into the tube being heated. A mirror surface formed immediately.

Part 2:.

(Proceeded from the formulae in part 1)

o

CH3CHOH  CH3CHO + H+ + 1 e-

o

CH3CHO + H20  CH3CHOHOH  CH3COOH(aq) + 2 H+ + 2 e-

 

(highly unstable because the second carbon has two -OH groups attached to it)

A) The distillate smelled strongly of vinegar. This is explained by the fact the CH3COOH(aq) is acetic acid, the acid in vinegar.

B) pH was 2.8, 0.1

C)Na2CO3 + CH3COOH  CH3COONa + H2CO3H20(l) + CO2 (g)

Effervescence occurred, since when the carbon dioxide then escapes, effervescence results. This is a similar reaction to what happens when you open a soda bottle, and the H2CO3 reacts with air.

Part 3:

NaOH

CH3CH2OH  CH3CHO

I2

I2 + 2 e- 2 I-

O O O

|| NaOH || H20 ||

CH3 - C - H  I3C - C - H + 3 H20  I3C - H + H - C - O-

I2 NaOH

For an iodoform reaction to occur, the substance has to have a carbonyl group with a methyl group attached to it. During the process, the carbon in H3C(-III) changes it’s oxidation number in order to bind the iodine, and it becomes I3C (+III), with 6 extra electrons gained in the process (C(-III)  C(+III) + 6 e-). The product smells of ether, and a precipitate forms.

Part 4:

2 CH3CH2OH + 2 Na+ 2 CH3CH2ONa + H2

Sodium reacted violently with the ethanol, the effervescence clearly visible. The a lit match was taken to the mouth of the testtube, it ‘popped’, which suggests that considerable amounts of hydrogen were present, as can be seen from the formula.