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Organic chemistry - Chemistry Form 4



In this lesson we will discuss alkanols.

Alkanols are also known as alcohols. They form a homologous series with the general formula CnH2n+1 OH
All the alkanols posses an -OH as the functional group.

The functional group is the group of atoms responsible for the characteristic reactions of compound.


1. Alkanols have a general formula of CnH2n+1 OH
Where n = 1,2,3,4,5 etc.
2. They have a hydroxyl (OH) group attached to a carbon atom which is bonded to hydrogen atoms or other carbon atoms.
a, b and d can be hydrogen atoms or carbon atoms.


3. Alkanol have their names ending with - ol. when naming alkanols the suffix -ol replaces the letter - e of alkanes.
The parent name of the alkanols depends on the number of carbon atoms in the structure of alkanol.


The following illustrations show the first three alkanols.


Example

The number 1 in the names Ethan-1-ol, Propan-l-ol, Butan - l -ol etc is used to show that the functional group is attached to the first carbon of the straight carbon chain.
When naming the alkanols, always count from the side that gives the -OH the lowest number for example.


Count from the side that gives the carbon containing the OH the lowest number, regardless of the position of the branches.
Hence the name for the above alkanol is:-2, 3 - dimethyl Butan - 2- ol

In general alkanols can be prepared by:-
1. Hydrolysis of alkenes: Ethanol can be manufactured from Ethene. Ethene is dissolved in concentrated sulphuric acid to form Ethyl Hydrogen Sulphate which on hydration forms Ethanol.This is shown by the following equation.



The Ethyl Hydrogen sulphate is then hydrolysed and distilled at 780C to obtain pure Ethanol.
This is shown by the following equation

C2H5HSO4(l) + H2O (l) C2H5OH(l) + H2SO4(aq)

Ethanol is produced on a large scale by the hydrolysis of ethene using steam. Ethene and steam are compressed to about 60 atmospheres and passed over immobilized phosphoric (v) acid at 3000C

C2H4(g) + H2O(l) C2H5OH(l)

Pure ethanol is obtained by fractional distillation of the mixture obtained.
The mixture of yeast and sugar is filtered to obtain the filtrate which is then fractional distilled to obtain pure Ethanol as shown.

Preparation of ethanol by fermentation of glucose
Procedure
1. Place sugar solution mixed with yeast in a conical flask.
2. Connect a delivery tube with a tight fitting cork to the conical flask and a boiling tube containing calcium Hydroxide solution.
3. Keep the apparatus for about 3 - 4 days.


Starch is mixed with water and malt and left to ferment for 3 to 4 days. The malt provides the enzyme diastase which converts starch to maltose.

The equation is shown below:
Maltose is then hydrolysed into glucose in the presence of yeast which provides the enzyme maltase.
The equation is shown below

The enzyme zymase from yeast then catalyses the fermentation of glucose into ethanol and carbon (IV) oxide.
The equation is shown below

To increase the alcoholic concentration from the fermented liquid they are distilled to produce spirits.

1. The members of the alkanol series are liquids at room temperature.
2. The boiling points and melting points of the alkanols increases with the increase in relative molecular mass. The boiling points are higher than those of alkanes with the same number of carbon atoms due to the hydrogen bonds present in the alkanol.
3. The hydrogen bond also make the solubility of alkanols higher than those of alkanes with the same number of carbon atoms.

The table below shows a summary of the physical properties of alkanols.

Combustion

Click to play the following video clip to observe how ethanol burns.


Ethanol is highly flammable and hence ignites readily when lit.
It burns in air with a blue flame to give carbon (IV) oxide and water.
No residue is left in watch glass. This is shown by the following equation.

C2H5OH(l) + 3O2 (g) 2CO2 (g) + 3H2O(g)

Reaction with Sodium

Click to play the following video clip to observe how ethanol reacts with Sodium .


 

When sodium reacts with Ethanol, it sinks and does not melt. Effervescence occurs and hydrogen gas is evolved.
At the end a clear solution of sodium ethoxide is left in the tube. This is shown by the following equation
Ethanol + sodium w Sodium Ethoxide + Hydrogen

2C2H5OH(l) + 2Na (s) 2C2H5ONa(aq)+ H2(g)
Alkanols react with metals at the top of reactivity series e.g. (Ca, Na and K) to form metal Ethoxides and Hydrogen gas.

Reaction with concentrated Sulphuric acid

Concentrated sulphuric acid reacts with Ethanol at 1800c to form Ethene and water. This is a dehydration reaction. This is illustrated by the equation below;

All Alkanols react with concentrated sulphuric acid to form Alkenes and water.

The following video clip shows the reaction between alkanols with alkanoic acid.

Click to play the video and observe what happens carefully.


Ethanoic acid react with Ethanol to form a sweet smelling oily liquid known as Ethyl Ethanoate (ester) and water.
Ethanol loses the Hydrogen of the hydroxyl group while Ethanoic acid loses the OH group of the carboxyl group to form water while their remaining parts join to form Ethyl ethanoate.
The equation is as follows:


Concentrated sulphuric acid is used as a catalyst to speed up the reaction.
NOTE
In general, a reaction between alcohol and carboxylic acid produces an ester and water. The process is known as esterification.

The video clip below shows the oxidation of ethanol. Click to play the video and observe what happens carefully.


When Potassium dichromate (VI) is added to Ethanol, its colour changes from orange to Green. When acidified potassium manganate (VII) is added to ethanol the purple colour changes to colourless. Oxidizing agents such as Potassium dichromate (VI) and potassium manganate (VII) oxidize alkanols to alkanoic acids.

The following are some of the uses of Ethanol.

Ethanol has the following uses:

  • As an antiseptic in specified concentrations
  • Used as a fuel
  • Used as a solvent
  • Manufacture of Varnishes e.g. Ink, glue etc
  • Manufacture of deodorants, perfumes because it evaporates easily
  • Ethanol is used in alcoholic drinks e.g. beer wines and spirits.


In this lesson we will discuss alkanoic acids.

They are also referred to as carboxylic acids and have a general formula

The functional group for alkanoic acids is


When the the value of n= 0, the molecular formula of the alkanoic acid will be CH2O2 and the structural formula will be;

Methanoic acid

When n=1 the molecular formula will be C2H4O2 and the structural formula will be;

Ethanoic acid

When n= 3 the molecular formula will be C3H6O2 and the structural formula will be;


Propanoic acid


Alkanoic acids are named as if they are derived from alkanes through replacement of the letter 'e' with 'oic' of the alkanes with the same number of carbon atoms as the acid.
Unlike the alkanols the functional group can only be at the end of the carbon chain.


The first ten straight chain alkanoic acids are liquids at room temperature.

The first few members like methanoic acid and ethanoic acids are soluble in water. The rest are insoluble and float in water. The solubility of alkanoic acids generally decreases with increasing molecular mass.

To prepare ethanoic acids by oxidation of ethanol.

Click to play the following video clip showing some tests carried out to investigate the chemical properties of alkanoic acids.


 

Ethanoic acid has a pH 4.7
Conclusion
Ethanoic acid is a weak acid. It partially dissociate into ions in water as shown by the following equation.

CH3COOH (l) CH3COO-(aq) + H+(aq)

The following video clip shows the reaction of ethanoic acid with Magnesium ribbon.

Click to play the video and observe what happens.


Effervescence of a colourless gas which puts off a burning splint with a pop sound occurs. The gas is hydrogen.
Conclusion
Magnesium displaces hydrogen from ethanoic acid to form magnesium ethanoate and hydrogen gas as shown in the following equation.

2CH3COOH(l)  + Mg (s) (CH3COO)2Mg + H2(g)

NOTE: That the metal displaces hydrogen in the -COOH group and not the other hydrogen.
Metals at the top of series react with alkanoic acids to form metal alkanoates and hydrogen gas as shown below;

Alkanoic acid + Metal w Metal alkanoate + Hydrogen

The following video clip shows the reaction between ethanoic acid and sodium hydrogen carbonate.

Click to play the video to observe what happens.


Observation
When ethanoic acid is reacted with Sodium hydrogen carbonate effervescence occurs and a colourless gas produced which forms white precipitate with lime water. The gas is carbon (IV) oxide as shown in the following equation.

CH3COOH(l) + NaHCO3(aq) CH3COONa(aq) + CO2(g) + H2O (l)
 

NOTE: Like mineral acids, Carboxylic acids react with Carbonates to form a salt which is the alkanoate, carbon (IV) oxide and water.

The video clip below shows the reaction between ethanol and ethanoic acid.

Click to play the video to observe what happens.


A sweet smelling compound called an ester is formed

Ethanoic acid will react with ethanol in the presence of a few drops of concentrated sulphuric acid to form ethyl ethanoate and water.

NOTE:

1) Ethyl ethanoate is one example of an ester
2) Alkanoic acids react with alkanols to form alkyl alkanoate ester and water.
3) Always remember that the first part of the ester is derived from the acid while the second part is derived from the alcohol. In writing the name of the esters we start with alcohol part with the acid part..

The following are some of the uses of alkanoic acid.



In this lesson we will discuss various detergents.

Detergent fall into 2 main groups;

Soapy detergents (Soaps)

Soapless detergents (Detergents)

Soaps are sodium or potassium salts of long chained alkanoic acids (fatty acids) such as Octadecanoic acid (stearic acid)

The video clip below shows the Laboratory preparation of soap. Observe what happens carefully.


Lather forms readily when warm distilled water is added to the soap followed by the warm tap water. Warm river water doesn't form lather but it forms scum with soap.
The white filtered solid is soap since it formed lather with warm distilled water.
When an alkali is boiled with a fat or oil, a hydrolysis reaction takes place according to the following equation;

When the hydrolysis reaction takes place in presence of sodium hydroxide, the process is referred to as saponification. The sodium salt of the acid is known as soap if the number of carbon atoms per molecule is more than eight.
Sodium chloride is added to separate the soap from glycerol, in a process known as salting out. The soap formed in the above experiment did not form lather with warm river water. This is due to the fact that some river water contains a high proportion hard water hence forming scum.

With distilled water however, lather is easily formed. Distilled water does not contain the cations (mg2+, Ca2+) that make the water hard.

Soap molecules have two dissimilar ends.
i) A hydrocarbon chain end which is non-polar and has no attraction for water.

ii) A carboxylate end which is polar and is attracted to water.

The non-polar end is oil soluble while the polar end is water soluble. Oil and water do not mix (immiscible). When oil is shaken with water, the particles of oil soon coalesce and float on the water surface. Let the soap anion be represented as a match stick structure with a long hydrocarbon chain (non-polar) (hydrophobic) water hating and a polar head (hydrophilic) water loving.

The head of the soap moving to the water and the tail remaining (being attracted to the oil)

When the mixture is thoroughly shaken, the soap anions surround each drop of soil as shown below.


Each oil drop has a large cloud of negative charge around it (Remember the polar head is negatively charged)
The oil drops therefore repel each other and this prevent the drop from coalescing.
When the washing process is taking place, the soap anions C17H35COO- become oriented on the surface of a small droplet of oily greasy dirt.

The water soluble groups on the surface of the droplets keep the droplets suspended (emulsified) in the in water.
During rinsing the water carries away the oil droplets.
Note: the cleansing agent is water, ordinary soap only helps the water to clean.

The mode of action of soapless detergent is the same as that of soapy detergent.
The hydrocarbon tail which is grease loving will dissolve in fats, grease or oil while the ionic head which is water loving dissolves readily in water as shown below;

.

The advantage soapless detergent have over soap is that they are not affected by hard water since the corresponding calcium and magnesium salts are soluble. Ordinary soap forms insoluble salts with cations present in hard water forming scum as shown in the following equations.

The video click below shows how a soapless detergent can be prepared in the laboratory.

Click to play the video and observe what happen carefully.


Sodium hydroxide is added to the alkylHydrogen sulphate to neutralize it to form sodium alkyl Sulphate which is a detergent and lather equally well with both tap water and distilled water as shown.

The soapless detergent in this experiment both form lather with tap water and distilled water since the corresponding calcium and magnesium salts are soluble.Olive oil reacts with concentrated Sulphuric acid to form alkylhydrogen sulphate as shown below in the following equations.


Soapless detergent can also be made from alcohol as shown in the equations below. The alcohol is reacted with sulphuric acid to form alkylhydrogen sulphate as shown

The alkylHydrogen Sulphate is neutralized by sodium Hydroxide to form the soapless detergent (Sodium Alkylsulphate as shown)

Soapless detergent with a branched chain alkyl group are not easily broken down by bacteria (non - biodegradable) and are therefore the cause of frothing in sewage plants, rivers. This disadvantage may be avoided by making the detergent from alkylbenzene with straight chain alkyl groups.

In this lesson we will discuss polymers.

By the end of the lesson, you should be able to
a) List some natural, synthetic polymers fibres and state their uses
b) Describe the preparation, properties and uses of some synthetic polymers
c) Identify the structure of a polymer given the monomer
d) State the advantages and disadvantages of synthetic materials compared to those of natural


The prefix, 'poly' means many or multiple. Some molecules can join together to form larger molecules.
Such large molecules which result from the combination of many smaller molecules (Monomers) are referred to as polymers. The process through which monomers join is known as polymerization.
There are two types of polymers. There are those that occur naturally and the synthetic or human made.

Addition polymerization
b) Condensation polymerization
1. Addition polymerization of some synthetic polymers.
Addition polymerization occurs when unsaturated molecules (monomers) join to form a long chain molecules (polymer) without the formation of any other product.

The following animation shows the different kinds of additional polymers.

Note
1. The double bonds between the carbon atoms are broken down enabling many molecules to join to each other to form a large molecule called a polymer.
2. n stands for the number of monomer combining which should be more than 2
3. The polymer is named after the monomer from which it is synthesized

Another example of a polymer is polystyrene as shown in this animation;

In condensational polymerization, monomers combine to form a long chain molecule (polymer) with the loss of small molecules like ammonia, water or hydrogen chloride. The monomer should have at least two functional groups so that molecules can join at both ends this permitting formation of a chain.

The following are examples of condensation polymers

Nylon is another example of a polymer and is shown in the following animation

The polymerization of Amino-acids involved two different monomers as show by the following animation.

The table below shows specific uses of various polymers.

The table below shows tha advantages and disadvantages of systhetic polymers and fibres

All living things contain polymers. Proteins, carbohydrates, wood and natural rubber are all polymers. These polymers are formed in nature.
Examples

The table below shows the advantages and disadvantages of natural polymers


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