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D.PHYSICAL AND CHEMICAL PROPERTIES OF ALKANOLS

    Use the prepared sample above for the following experiments that shows the characteristic properties of alkanols

  • Role of yeast

Yeast is a single cell fungus which contains the enzyme maltase and zymase that catalyse the fermentation process. 

  • Observations in lime water.

A white precipitate is formed that dissolve to a colourless solution later. Lime water/Calcium hydroxide reacts with carbon(IV)0xide produced during the fermentation to form insoluble calcium carbonate and water.

 More carbon (IV)0xide produced  during fermentation react with  the insoluble calcium carbonate and water to form soluble calcium hydrogen carbonate.

Ca(OH)2(aq)             +       CO2 (g)       ->      CaCO3(s)

H2O(l)    + CO2 (g)  +  CaCO3(s) ->         Ca(HCO3) 2 (aq)

       (c)Effects on litmus paper

         Experiment

Take the prepared sample and test with both blue and red litmus papers.

Repeat the same with pure ethanol and methylated spirit.

Sample Observation table

          Substance/alkanolEffect on litmus paper
Prepared sampleBlue litmus paper remain blue Red litmus paper remain red
Absolute ethanolBlue litmus paper remain blue Red litmus paper remain red
Methylated spiritBlue litmus paper remain blue Red litmus paper remain red

  Explanation 

Alkanols are neutral compounds/solution that have characteristic sweet smell and taste.

They have no effect on both blue and red litmus papers.

(d) Practical: Solubility of Alcohols in water.

Experiment

  Place about 5cm3 of prepared sample into a clean test tube Add equal amount of distilled water.

Repeat the same with pure ethanol and methylated spirit.

Observation

No layers formed between the two liquids.

Explanation

Ethanol is miscible in water.Both ethanol and water are polar compounds .

The solubility of alkanols decrease with increase in the alkyl chain/molecular mass.

The alkyl group is insoluble in water while –OH functional group is soluble in water.

As the molecular chain becomes longer ,the effect of the alkyl group increases as the effect of the functional group decreases.

e)Melting/boiling point.

Experiment

Place pure ethanol in a long boiling tube .Determine its boiling point.

Observation

Pure ethanol has a boiling point of 78oC at sea level/one atmosphere pressure.

Explanation

The melting and boiling point of alkanols increase with increase in molecular chain/mass .

This is because the intermolecular/van-der-waals forces of attraction between the molecules increase.

More heat energy is thus required to weaken the longer chain during melting and break during boiling.

f)Density

Density of alkanols increase with increase in the intermolecular/van-der-waals forces of attraction between the molecule, making it very close to each other.

This reduces the volume occupied by the molecule and thus increase the their mass per unit volume (density).

Summary table showing the trend in physical properties of alkanols

                 AlkanolMelting point (oC)Boiling point (oC)Density gcm-3Solubility in water
Methanol-98650.791soluble
Ethanol-117780.789soluble
Propanol-103970.803soluble
Butanol-891170.810Slightly soluble
Pentanol-781380.814Slightly soluble
Hexanol-521570.815Slightly  soluble
Heptanol-341760.822Slightly soluble
Octanol-151950.824Slightly soluble
Nonanol-72120.827Slightly soluble
Decanol62280.827Slightly soluble

      g)Practicals on Burning of Alkanols

Experiment

Place the prepared sample in a watch glass. Ignite. Repeat with pure ethanol and methylated spirit.

Observation/Explanation

Fermentation produce ethanol with a lot of water(about a ratio of 1:3)which prevent the alcohol from igniting.

Pure ethanol and methylated spirit easily catch fire / highly flammable.

They burn with an almost colourless non-sooty/non-smoky blue flame to form carbon(IV) oxide (in excess air/oxygen)or carbon(II) oxide (limited  air) and water.

Ethanol is thus a saturated compound like alkanes.

Chemica equation

   C2 H5OH(l)    +          3O2 (g)      -> 3H2O(l)    +      2CO2 (g)  ( excess air)

    C2 H5OH(l)    +         2O2 (g)      -> 3H2O(l)    +      2CO (g)  ( limited air)

    2CH3OH(l)    +          3O2 (g)      -> 4H2O(l)    +      2CO2 (g)  ( excess air)

    2 CH3OH(l)    +         2O2 (g)      -> 4H2O(l)    +      2CO (g)  ( limited air)

2C3 H7OH(l)    + 9O2 (g)      -> 8H2O(l)    +      6CO2 (g)  ( excess air)

    C3 H7OH(l)    +         3O2 (g)      -> 4H2O(l)    +      3CO (g)  ( limited air)

2C4 H9OH(l)    + 13O2 (g)      -> 20H2O(l)    + 8CO2 (g)  ( excess air)

    C4 H9OH(l)    +         3O2 (g)      -> 4H2O(l)    +      3CO (g)  ( limited air)

Due to its flammability, ethanol is used;

  • as a fuel in spirit lamps
  • as gasohol when blended with gasoline

(h)Formation of alkoxides

Experiment

Cut a very small piece of sodium. Put it in a beaker containing about 20cm3 of the prepared sample in a beaker.

 Test the products with litmus papers. Repeat with absolute ethanol and methylated spirit.

Sample observations

Substance/alkanolEffect of adding sodium
Fermentation prepared sample(i)effervescence/fizzing/bubbles (ii)colourless gas produced that extinguish burning splint with explosion/ “Pop” sound (iii)colourless solution formed (iv)blue litmus papers remain blue (v)red litmus papers turn blue
Pure/absolute ethanol/methylated spirit(i)slow effervescence/fizzing/bubbles (ii)colourless gas slowly  produced that extinguish burning splint with explosion/ “Pop” sound (iii)colourless solution formed (iv)blue litmus papers remain blue (v)red litmus papers turn blue

Explanations

Sodium/potassium reacts slowly with alkanols to form basic solution called alkoxides and producing hydrogen gas.

 If  the alkanol has some water the metals react faster with the water to form soluble hydroxides/alkalis i.e.

Sodium       +       Alkanol      ->     Sodium alkoxides                + Hydrogen gas

Potassium  +      Alkanol      ->      Potassium alkoxides    + Hydrogen gas

Sodium       +       Water          ->     Sodium hydroxides          + Hydrogen gas

Potassium  +      Water         ->      Potassium hydroxides        + Hydrogen gas

Examples

1.Sodium metal reacts with ethanol to form sodium ethoxide

Sodium metal reacts with water to form sodium Hydroxide

2CH3CH2OH(l)   +       2Na(s)        ->      2CH3CH2ONa (aq)    + H2 (s)

2H2O(l)      +       2Na(s)        ->      2NaOH (aq)    + H2 (s)

2.Potassium metal reacts with ethanol to form Potassium ethoxide

Potassium metal reacts with water to form Potassium Hydroxide

2CH3CH2OH(l)   +       2K(s)          ->      2CH3CH2OK (aq)    + H2 (s)

2H2O(l)      +       2K(s)          ->      2KOH (aq)    + H2 (s)

3.Sodium metal reacts with propanol to form sodium propoxide

Sodium metal reacts with water to form sodium Hydroxide

2CH3CH2 CH2OH(l)     +       2Na(s) -> 2CH3CH2 CH2ONa (aq)    + H2 (s)

2H2O(l)      +       2Na(s)        ->      2NaOH (aq)    + H2 (s)

4.Potassium metal reacts with propanol to form Potassium propoxide

Potassium metal reacts with water to form Potassium Hydroxide

2CH3CH2 CH2OH(l)     +       2K(s)          -> 2CH3CH2 CH2OK (aq)    + H2 (s)

2H2O(l)      +       2K(s)          ->      2KOH (aq)    + H2 (s)

5.Sodium metal reacts with butanol to form sodium butoxide

Sodium metal reacts with water to form sodium Hydroxide

2CH3CH2 CH2 CH2OH(l)  + 2Na(s) -> 2CH3CH2 CH2 CH2ONa (aq)    + H2 (s)

2H2O(l)      +       2Na(s)        ->      2NaOH (aq)    + H2 (s)

6.Sodium metal reacts with pentanol to form sodium pentoxide

Sodium metal reacts with water to form sodium Hydroxide

2CH3CH2 CH2 CH2 CH2OH(l)+2Na(s) -> 2CH3CH2 CH2 CH2 CH2ONa (aq) + H2 (s)

2H2O(l)      +       2Na(s)        ->      2NaOH (aq)    + H2 (s)

(i)Formation of Esters/Esterification

Experiment

Place 2cm3 of ethanol in a boiling tube.

Add equal amount of ethanoic acid.To the mixture add carefully 2drops of concentrated sulphuric(VI)acid.

Warm/Heat gently.

Pour the mixture into a beaker containing about 50cm3 of cold water.

Smell the products.

 Repeat with methanol

Sample observations

Substance/alkanolEffect on adding equal amount of ethanol/concentrated sulphuric(VI)acid
Absolute ethanolSweet fruity smell
MethanolSweet fruity smell

Explanation

Alkanols react with alkanoic acids to form a group of homologous series of sweet smelling compounds called esters and water. This reaction is catalyzed by concentrated sulphuric(VI)acid in the laboratory.

Alkanol      +    Alkanoic acid   –Conc. H2SO4->    Ester   +  water

 Naturally esterification is catalyzed by sunlight. Each ester has a characteristic smell derived from the many possible combinations of alkanols and alkanoic acids that create a variety of known natural(mostly in fruits) and synthetic(mostly in juices) esters .

Esters derive their names from the alkanol first then alkanoic acids. The alkanol “becomes” an alkyl group and the alkanoic acid “becomes” alkanoate hence alkylalkanoate. e.g.

          Ethanol       +       Ethanoic acid       ->      Ethylethanoate      +    Water

          Ethanol       +       Propanoic acid     ->      Ethylpropanoate    +    Water

          Ethanol       +       Methanoic acid    ->      Ethylmethanoate   +     Water

          Ethanol       +       butanoic acid       ->      Ethylbutanoate      +     Water

          Propanol     +       Ethanoic acid       ->      Propylethanoate  +     Water

          Methanol    +       Ethanoic acid       ->      Methyethanoate   +     Water

          Methanol    +       Decanoic acid      ->      Methyldecanoate +     Water

          Decanol      +       Methanoic acid    ->      Decylmethanoate          +      Water

During the formation of the ester, the “O” joining the alkanol and alkanoic acid comes from the alkanol.

          R-COOH   +    R2 –OH     ->    R-COO –R2    +  H2O

e.g.

1. Ethanol reacts with ethanoic acid to form the ester ethyl ethanoate and water.

          Ethanol       + Ethanoic acid    –Conc. H2SO4 –>Ethylethanoate + Water

         C2H5OH (l) + CH3COOH(l) –Conc. H2SO4 –>  CH3COO C2H5(aq)   +H2O(l)

CH3CH2OH (l)+ CH3COOH(l) –Conc. H2SO4 –>  CH3COOCH2CH3(aq)   +H2O(l)

2. Ethanol reacts with propanoic acid to form the ester ethylpropanoate and water.

          Ethanol       + Propanoic acid –Conc. H2SO4 –>Ethylethanoate + Water

C2H5OH (l)+ CH3 CH2COOH(l) –Conc. H2SO4 –>CH3CH2COO C2H5(aq)   +H2O(l)

CH3CH2OH (l)+ CH3 CH2COOH(l) –Conc. H2SO4 –>  CH3 CH2COOCH2CH3(aq)   +H2O(l)

3. Methanol reacts with ethanoic acid to form the ester methyl ethanoate and water.

          Methanol    + Ethanoic acid    –Conc. H2SO4 –>Methylethanoate + Water

         CH3OH (l)  + CH3COOH(l) –Conc. H2SO4 –>  CH3COO CH3(aq)   +H2O(l)

4. Methanol reacts with propanoic acid to form the ester methyl propanoate and water.

          Methanol    + propanoic acid –Conc. H2SO4 –>Methylpropanoate + Water

 CH3OH (l)+ CH3 CH2COOH(l) –Conc. H2SO4 –> CH3 CH2COO CH3(aq)   +H2O(l)

5. Propanol reacts with propanoic acid to form the ester propylpropanoate and water.

          Propanol     + Propanoic acid –Conc. H2SO4 –>Ethylethanoate + Water

C3H7OH (l)+ CH3 CH2COOH(l) –Conc. H2SO4 –>CH3CH2COO C3H7(aq)   +H2O(l)

CH3CH2 CH2OH (l)+ CH3 CH2COOH(l) –Conc. H2SO4 –> CH3 CH2COOCH2 CH2CH3(aq)   +H2O(l)

(j)Oxidation

Experiment

Place 5cm3 of absolute ethanol in a test tube.Add three drops of acidified potassium manganate(VII).Shake thoroughly for one minute/warm.Test the solution mixture using pH paper. Repeat by adding acidified potassium dichromate(VII).

Sample observation table

Substance/alkanolAdding acidified KMnO4/K2Cr2O7pH of resulting solution/mixtureNature of resulting solution/mixture
Pure ethanol(i)Purple colour of KMnO4decolorized   (ii) Orange colour of K2Cr2O7turns green.pH= 4/5/6     pH = 4/5/6Weakly acidic     Weakly acidic    

Explanation

Both acidified KMnO4 and K2Cr2O7 are oxidizing agents(add oxygen to other compounds. They oxidize alkanols to a group of homologous series called alkanals then further oxidize them to alkanoic acids.The oxidizing agents are themselves reduced hence changing their colour:

          (i) Purple KMnO4 is reduced to colourless Mn2+

          (ii)Orange K2Cr2O7is reduced to green Cr3+

The pH of alkanoic acids show they have few H+ because they are weak acids i.e

Alkanol      +       [O]   ->      Alkanal      +       [O]    ->      alkanoic acid

    NB The [O] comes from the oxidizing agents acidified KMnO4 or K2Cr2O7

Examples

1.When ethanol is warmed with three drops of acidified KMnO4 there is decolorization of KMnO4

     Ethanol    +     [O]    ->     Ethanal      +    [O]     ->   Ethanoic acid

CH3CH2OH  +    [O]    ->   CH3CH2O    +    [O]     ->   CH3COOH

 2.When methanol is warmed with three drops of acidified K2Cr2O7 ,the orange colour of acidified K2Cr2O7 changes to green.

     methanol    +     [O]    ->     methanal      +    [O]     ->   methanoic acid

       CH3OH    +     [O]    ->         CH3O       +    [O]     ->   HCOOH

3.When propanol is warmed with three drops of acidified K2Cr2O7 ,the orange colour of acidified K2Cr2O7 changes to green.

     Propanol    +     [O]    ->     Propanal      +    [O]     ->   Propanoic acid

CH3CH2 CH2OH  +    [O]    ->  CH3CH2 CH2O  +  [O]   -> CH3 CH2COOH

4.When butanol is warmed with three drops of acidified K2Cr2O7 ,the orange colour of acidified K2Cr2O7 changes to green.

     Butanol    +     [O]    ->     Butanal      +    [O]     ->   Butanoic acid

CH3CH2 CH2 CH2OH + [O]  ->CH3CH2 CH2CH2O+[O] -> CH3 CH2COOH

Air slowly oxidizes ethanol to dilute ethanoic acid commonly called vinegar. If beer is not tightly corked, a lot of carbon(IV)oxide escapes and there is slow oxidation of the beer making it “flat”.

(k)Hydrolysis /Hydration and Dehydration

I. Hydrolysis/Hydration is the reaction of a compound/substance with water.

Alkenes react with water vapour/steam at high temperatures and high pressures in presence of phosphoric acid catalyst to form alkanols.i.e.

Alkenes      +       Water         – H3PO4 catalyst->          Alkanol

Examples

(i)Ethene is mixed with steam over a phosphoric acid catalyst at 300oC temperature and 60 atmosphere pressure to form ethanol

      Ethene        + water    —60 atm/300oC/ H3PO4      –> Ethanol

H2C =CH2 (g)  +  H2O(l)   –60 atm/300oC/ H3PO4        –>   CH3 CH2OH(l)

This is the main method of producing large quantities of ethanol instead of fermentation

(ii) Propene        + water    —60 atm/300oC/ H3PO4      –> Propanol

CH3C =CH2 (g)  +  H2O(l)   –60 atm/300oC/ H3PO4        –>   CH3 CH2 CH2OH(l)

(iii) Butene        + water    —60 atm/300oC/ H3PO4      –> Butanol

CH3 CH2 C=CH2 (g) + H2O(l)   –60 atm/300oC/ H3PO4   –> CH3 CH2 CH2 CH2OH(l)

II. Dehydration is the process which concentrated sulphuric(VI)acid (dehydrating agent) removes water from a compound/substances.

Concentrated sulphuric(VI)acid dehydrates alkanols to the corresponding alkenes at about 180oC. i.e

Alkanol  –Conc. H2 SO4/180oC–> Alkene  + Water

Examples

1. At 180oC and in presence of Concentrated sulphuric(VI)acid, ethanol undergoes dehydration to form ethene.

                    Ethanol              —180oC/ H2SO4      –>    Ethene              +   Water

                 CH3 CH2OH(l)         –180oC/ H2SO4        –>    H2C =CH2 (g)  +  H2O(l)

2. Propanol undergoes dehydration to form propene.

                    Propanol              —180oC/ H2SO4      –>    Propene              +   Water

                 CH3 CH2 CH2OH(l)  –180oC/ H2SO4        –>    CH3CH =CH2 (g)  +  H2O(l)

 3. Butanol undergoes dehydration to form Butene.

                    Butanol              —180oC/ H2SO4      –>    Butene              +   Water

                 CH3 CH2 CH2CH2OH(l)         –180oC/ H2SO4        –>    CH3 CH2C =CH2 (g)  +  H2O(l)

3. Pentanol undergoes dehydration to form Pentene.

                    Pentanol              —180oC/ H2SO4     –>    Pentene              +   Water

CH3 CH2 CH2 CH2 CH2OH(l)–180oC/ H2SO4–>CH3 CH2 CH2C =CH2 (g)+H2O(l)

 (l)Similarities of alkanols with Hydrocarbons

 I. Similarity with alkanes

Both alkanols and alkanes burn with a blue non-sooty flame to form carbon(IV)oxide(in excess air/oxygen)/carbon(II)oxide(in limited air)  and water. This shows they are saturated with high C:H ratio. e.g.

Both ethanol and ethane ignite and burns in air with a blue non-sooty flame to form carbon(IV)oxide(in excess air/oxygen)/carbon(II)oxide(in limited air)  and water.

 CH2 CH2OH(l)   +  3O2(g)   -Excess air->    2CO2 (g) +  3H2 O(l)

 CH2 CH2OH(l)   +  2O2(g)   -Limited air->    2CO(g) +  3H2 O(l)

CH3 CH3(g)   +    3O2(g)   -Excess air->     2CO2 (g) +  3H2 O(l)

2CH3 CH3(g)   +  5O2(g)   -Limited air->    4CO(g)  +  6H2 O(l)

II. Similarity with alkenes/alkynes

Both alkanols(R-OH) and alkenes/alkynes(with = C = C = double and  – C = C- triple ) bond:

          (i)decolorize acidified KMnO4

          (ii)turns Orange acidified K2Cr2O7  to green.

Alkanols(R-OH) are oxidized to alkanals(R-O) ant then alkanoic acids(R-OOH).

Alkenes are oxidized to alkanols with duo/double functional groups.

Examples

1.When ethanol is warmed with three drops of acidified K2Cr2O7 the orange of acidified K2Cr2O7 turns to green. Ethanol is oxidized to ethanol and then to ethanoic acid.

     Ethanol          +     [O]    ->     Ethanal      +    [O]     ->   Ethanoic acid

     CH3CH2OH  +     [O]    ->   CH3CH2O    +    [O]     ->   CH3COOH

2.When ethene is bubbled in a test tube containing acidified K2Cr2O7 ,the orange of acidified K2Cr2O7 turns to green. Ethene is oxidized to ethan-1,2-diol.

  Ethene      +    [O]      ->      Ethan-1,2-diol.

H2C=CH2      +    [O]        ->  HOCH2 -CH2OH

III. Differences with alkenes/alkynes

Alkanols do not decolorize bromine and chlorine water.

Alkenes decolorizes bromine and chlorine water to form halogenoalkanols

Example

When ethene is bubbled in a test tube containing bromine water,the bromine water is decolorized. Ethene is oxidized to bromoethanol.

  Ethene      +   Bromine water        ->      Bromoethanol.

H2C=CH2      +    HOBr                    ->      BrCH2 -CH2OH

IV. Differences in melting and boiling point with Hydrocarbons

Alkanos have higher melting point than the corresponding hydrocarbon (alkane/alkene/alkyne)

This is because most alkanols exist as dimer.A dimer is a molecule made up of two other molecules joined usually by van-der-waals forces/hydrogen bond or dative bonding.

Two alkanol molecules form a dimer joined by hydrogen bonding.

Example

In Ethanol the oxygen atom attracts/pulls the shared electrons in the covalent bond more to itself than Hydrogen.

 This creates a partial negative charge (δ-) on oxygen and partial positive charge(δ+) on hydrogen.

Two ethanol molecules attract each other at the partial charges through Hydrogen bonding forming a dimmer.

Hydrogen bonds

          H       H           H

Covalent bonds

H       C       C       O                H       H      

          H       H           H     O     C       C       H

                                                H       H

Dimerization of alkanols means more energy is needed to break/weaken the Hydrogen bonds before breaking/weakening the intermolecular forces joining the molecules of all organic compounds during boiling/melting.

E.USES OF SOME ALKANOLS

(a)Methanol is used as industrial alcohol and making methylated spirit

(b)Ethanol is used:

          1. as alcohol in alcoholic drinks e.g Beer, wines and spirits.

          2.as antiseptic to wash woulds

          3.in manufacture of vanishes, ink ,glue and paint because it is volatile and thus easily evaporate

          4.as a fuel when blended with petrol to make gasohol.