Chemical properties of Ethanol.doc
Chemical properties of Ethanol & Phenol
Objective
To find out the chemical properties and pH of ethanol and phenol, and compare their differences between ethanol and phenol.
Results
Reaction of ethanol:
Properties / Reactions
Observations / Smell
Corresponding equations (if any)
pH of solution
universal indicator remains green, pH=7
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Triiodomethane reaction
yellow precipitate found at bottom of test-tube, with odour smell
C2H5OH + 4I2 + 6NaOH › CHI3(s) + HCOO-Na+ + 5NaI + 5H2O
Reaction with Na
Na sinks to bottom, colourless gas, which gives a 'pop' sound to burning splint, evolves slowly and moderately. When ethanol-ethoxide mixture in test-tube is poured onto a petri-dish, small, colourless rectangular-shaped crystals are formed in a few minutes.
2C2H5OH + 2Na › 2C2H5O-Na+ + H2(g)
Esterification
When the mixture of ethanol, ethanoic acid & conc.H2SO4 in test-tube is poured into Na2CO3 solution, a smell like all-purpose adhesive is noticeable.
Reaction of phenol:
Properties / Reactions
Observations / Smell
Corresponding equations (if any)
Solubility in water:
(a) a little phenol
(b) a lot of phenol
phenol dissolves gradually on shaking
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insoluble, phenol forms oil-like droplets on shaking (soluble when heated)
pH of solution
universal indicator changes from green to orange, i.e. acidic
Reaction with NaHCO3
phenol becomes insoluble after adding NaHCO3 and forms a emulsion on shaking
Reaction with NaOH
Solubility of phenol in NaOH is much higher than in water. After adding conc. HCl, phenol becomes insoluble (appear as droplets) again.
Reaction with Na
Na floats and evolves a colourless gas, which has a 'pop' sound on burning splint test, gradually (but faster than in ethanol)
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insoluble, phenol forms oil-like droplets on shaking (soluble when heated)
pH of solution
universal indicator changes from green to orange, i.e. acidic
Reaction with NaHCO3
phenol becomes insoluble after adding NaHCO3 and forms a emulsion on shaking
Reaction with NaOH
Solubility of phenol in NaOH is much higher than in water. After adding conc. HCl, phenol becomes insoluble (appear as droplets) again.
Reaction with Na
Na floats and evolves a colourless gas, which has a 'pop' sound on burning splint test, gradually (but faster than in ethanol)
Reaction with bromine water
Br2 decolourized readily in presence or absence of light, which indicates that this is not a free radical substitution reaction. A white precipitate is formed.
Reaction with 'neutral' FeCl3
The colour of FeCl3 changes from yellow to violet. The same colour change is not take place in ethanol.
*The violet complex formed between phenol and Fe3+ is still not well-known
Precaution
1.> The filter paper, which have been soaked with paraffin oil on sodium metal, should be thrown properly since the unreacted sodium remains on
the paper may cause a fire.
2.> Ensure that all sodium is reacted in test-tube before disposing the liquid.
3.> Avoid adding too large sodium to ethanol or phenol since the reaction may be to vigorous.
4.> Avoid contact with the crystal of phenol. If you contact with it accidentally, wash your hands with glycerol or plenty of water, or your hands
may have white strain due to phenol's corrosive property.
Discussion
1.> The smell of phenol is close to that in hospital.
2.> Both pH test (acidic in phenol, neutral in ethanol), iodoform test (+ve in ethanol), solubility test (miscible between ethanol & water), reaction with
NaHCO3 (phenol is insoluble), reaction with Br2 water (phenol decolourize Br2) and reaction with neutral FeCl3 (Fe3+ and phenol forms a
violet complex) can distinguish between ethanol & phenol.
3.> Phenol is much more soluble in NaOH than in water because the reaction between phenol and water to form H3O+ & phenoxide is reversible
(since phenol is a weak acid, most H+ formed will combine with phenoxide to form phenol again) whereas that between phenol and NaOH is not
and the formation of phenoxide ion is promoted:
Na+ & phenoxide ions are then dispersed by water molecules, thus phenol is highly soluble in NaOH.
4.> Compare their reactions with Na, H2 evolves faster in phenol than in ethanol due to the acidic nature of phenol. The acidity of an acid is depends
on the relative stabilities of the acid (HA) & its conjugate base (A-). The more stable the conjugate base A-, the stronger is the acid. In case of
phenol, the phenoxide ion is stabilized by delocalization of p-electrons (the charge on O is more disperse & lower its charge density):
The equilibrium of shifts to right and thus phenol is acidic.
However, in case of ethanol, alkyl group is electron-donating group, which makes ethoxide ion unstable (C2H5›O-), thus it's neutral.
5.> In the reaction with NaOH, the further addition of conc. HCl makes phenol becomes insoluble again which shows that phenol is a weaker acid
than mineral acids.
6.> Phenol has an electron-rich centre (benzene ring) to attract electrophiles to attack and electron-donating hydroxyl group further increase its
nucleopilicity. This makes phenol has a much higher reactivity than benzene and react with Br2 readily even in the absence of catalyst & light.
On the other hand, ethanol is saturated and has no electron-rich centre, thus no reaction between ethanol and Br2.
7.> Some of the reactions in this experiment is useful and is usually used for daily life. For example,
(a) Iodoform reaction is used to prepare a compound that is one carbon less than previous one and iodoform itself can be used as pesticide.
(b) Phenol and it's derivatives can be used as antiseptics so it's quite common to smell their smell in hospital.
(c) Esterification can be used to synthesize esters in perfumes.
(d) Phenol can be purified by adding NaOH to phenol and organic compound mixtures, sodium phenoxide can then be crystallized and
separated, phenol is regenerated by adding H+.
(e) FeCl3, Br2 and NaOH are used to test the presence of phenol if all these three tests show positive result.
Conclusion
Both ethanol and phenol are widely used compounds, especially in disinfectant. To distinguish them, several tests are needed, since other compounds may also be positive on these tests. If all of these test shows positive result, then the uncertain organic compound may be either one of them.
