Making ethanol

 

Practical

1)    Hydration of ethene:

 

 2)    Fermentation:

Uses of alcohols:

Ethanol in alcoholic drinks:

Ethanol as a fuel:

Ethanol in methylated spirits:

Uses of methanol:

Questions  P149  Qu 1-5

 

Properties of alcohols

 

Physical properties:

Volatility and boiling points:

Solubility:

Classification of alcohols:

 

Primary (1o)

Butan 1 ol.  This is a Primary (1o) alcohol.  When the OH carbon (*) is attached to only 1 other carbon atom.

Secondary (2o)

Propan 2 ol.  This is a Secondary (2o) alcohol.  When the OH carbon (*) is attached to 2 other carbon atoms.

Tertiary (3o)

2 Methylbutan 2 ol.  This is a Tertiary (3o) alcohol.  When the OH carbon (*) is attached to 3 other carbon atoms.

Questions  P151  Qu1-3

 

Combustion and oxidation of alcohols

 

The combustion of alcohols:

  C2H5OH(l) + O2(g) 2CO2(g) + 3H2O(g)
C 2       1 x2 = 2    
H 6           2 x3 =6
O 1   2   4 + 3
O (7-1 = 6)   2 x3  = 6   = 7  

Oxidation of alcohols:

 

Demo:

                                      Cr6+(aq)         +          3e-                   Cr3+(aq)

                                      Orange                                              Green

Primary alcohols:

 

Practical

 

Practical

    1a)    Primary alcohol Aldehyde:

  • The aldehyde has to be distilled off as it forms as it can be oxidised further.

 

 

    1b)    Primary alcohol Carboxylic acid:

  • When making the carboxylic acid the mixture is refluxed.

  • We do not need to worry about oxidising the aldehyde as we need to do this to reach the carboxylic acid.

 

Refluxing allows you to heat / boil volatile liquids for a long time.  The condenser stops the volatile liquids evaporating off. Distillation evaporates and condenses liquids at different temperatures.  Collect the liquid you want around its boiling point and discard any others

 

    2)  Secondary alcohols:

    3)  Tertiary alcohols:

        As you saw in the demo:  Tertiary alcohols cannot be oxidised

 

Summary of alcohol oxidation

Primary alcohol                         Aldehyde                         Carboxylic acid

 

Secondary alcohol                  Ketone                            No reaction

 

Tertiary alcohol                        No reaction

 

 

Questions:  P153  Qu1-3

 

Esterification and dehydration of alcohols

 

Esterification:

 

Esters:

 

Preparing an ester:

  • These can easily be prepared by adding 1cm3 of each of the carboxylic acid and alcohol in a boiling tube as shown in the diagram.
  • A few drops of concentrated sulphuric acid catalyst is added to the mixture and heated at 80oC for ~5 mins.
  • pouring the contents into a beaker of cold water will show the ester floating as an oil on the surface.

 

Practical

 

Dehydration of an alcohol:

 

Practical

 

Produce a flowchart for the reactions of the alcohols

 

Questions P155  Qu 1 - 3  /  P179  Qu 1 - 6

 

 

Introduction to halogenoalkanes

 

Naming the halogenoalkanes

         When a hydrogen is replaced by a halogen, the prefix fluoro-, chloro-, bromo- and iodo- are used:-

                                  CH3 Cl                      Chloromethane

                                  CH3 CH2Br               Bromoethane

         2 isomers can be derived from a monosubstituted propane:-

                                  CH3 CH2 CH2Cl    1 Chloropropane

                                  CH3 CHCl CH3     2 Chloropropane

         Multi halogen substituted compounds use di, tri to indicate how many of that halogen is present in the compound:-

                                  CH2Br CH2Br           1,2 - dibromoethane

 Reactivity of the halogenoalkanes:

Bond enthalpy

  • Weaker bonds break more easily.

  • Meaning more of them will break at the same temperature.

Bond polarity

  • Greater electronegativity makes a larger d-, meaning the carbon will have a larger d+.
  • Attracts nucleophiles more

Hydrolysis of halogenoalkanes:

        Hydrolysis:  is a reaction with water or aq hydroxide ions that break a chemical compound into two compounds

 

Questions  P157  Qu1 - 3

Reactions of the halogenoalkanes

Practical

Nucleophilic substitution reactions:  Hydrolysis

The mechanism:

Similarly with chloromethane (or any halogenoalkane):

Rate of hydrolysis of primary halogenoalkanes:

  CH3CH2CH2CH2Cl(aq) + H2O(aq) CH3CH2CH2CH2OH(aq) + H+(aq) + Cl-(aq)
  Ag+(aq) + Cl-(aq) AgCl(s)
          White ppt
The procedure:
  • Measure an equal amount of each of the halogenalkane and place in a water bath at 50oC.
  • Put another tube of ethanol, water and silver nitrate into another tube and place in the water bath.
  • Once all the tubes have reached the same temperature add an equal amounts of the silver nitrate mixture to each of the 3 halogenoalkanes.
  • Start timing and record the times at which each of the precipitates form.
  • The order of which the precipitates appear is indicated in the diagram to the left.
3 2 1

Polarity vs bond enthalpy (energy):

    1)  Polarity:

         Electronegativity of the halogens decreases as you go down group 7. 

This means that the C Cl bond will be more polar than the C Br bond which will be more polar than the C I bond:

 

                                  d+   d-                  d+   d-               d+  d-

                                  C Cl        >          C Br        >       C I

    2)  Bond enthalpy (energy):

                                  E(C Cl)   =  340 KJ mol-1

                                  E(C Br)   =  280 KJ mol-1

                                  E(C I)      =  240 KJ mol-1

Bond enthalpies:

Questions  P159  Qu1-3

Halogenoalkanes and the environment:

Halogen - containing polymers:

1)    PTFE - poly(tetrafluoroethane)

2)    PVC poly(chloroethene):

Chlorofluorocarbons, CFC's - enter Thomas Midgley

Trouble with CFCs

         CFCs have a devastating effect on the ozone layer.

         The ozone layer filters out harmful UV light which can cause skin cancer.

         CFCs were used in refrigeration and aerosol propellants. 

         The stability of CFCs has been the problem and the concentration has slowly built up in the atmosphere.

         In the stratosphere CFCs absorb UV light forming chlorine radicals.

         It is these chlorine radicals that break down ozone to oxygen:

The ozone layer

 

  • Ozone is 3 oxygen atoms joined together.
  • We are producing ozone where we don't want it and destroying it where we do want it.
  • Low level ozone in the troposphere causes respiratory problems.
  • The destruction of high level ozone allows harmful UV radiation to reach earth.
  • Ozone acts like a big pair of sunglasses filtering out most of the harmful UV radiation. 
  • Prior to the formation of ozone our planet was scorched and no life could survive.
  • UV radiation is divided into a, b, and c. 
  • C is the most harmful and is blocked out completely by ozone.
  • A is the weakest and only a small amount is absorbed by ozone.  This is the one that gives you a tan and ages your skin prematurely.

Ozone formation:

  O2(g) + UV 2O(g)            
  O(g) + O2(g) O3(g) + Heat        

How the ozone layer works:

  O3(g) + UV O2(g) + O(g)        
  O(g) + O2(g) O3(g) + Heat        
  O(g) + O2(g) D O3(g)            

Removal of ozone:

  O(g) + O3(g) 2O2(g)            

Ozone depletion

1)  CFC's:

             CF2Cl2                      CF2Cl.       +          Cl.

             Cl.              +                O3                          ClO.           +                    O2              Step 1

 

             ClO.           +                O                            Cl.              +                    O2              Step 2

 

Overall

 

  O(g) + O3(g) 2O2(g)            

2)  Nitrogen oxide:

             .NO              +                O3                           .NO2            +                    O2              Step 1

 

             .NO2           +                O                            .NO              +                    O2              Step 2

 

Overall

 

  O(g) + O3(g) 2O2(g)            

 

 The way forward - alternatives to CFCs

  • HCFCs are being used as a temporary replacement until something more suitable is found

  • Again they are non toxic and non - flammable.

  • They do still deplete ozone but are only about a tenth of the amount.

Ozone friendly products:

Questions  P161  Qu1-3 / P179  Qu7-12