Monday, November 11, 2013

Functional group of carbon compound for class 10th CBSE/NCERT

Functional group of carbon compound & Some important organic compound _Ethanol and Ethanoic acid

Functional group may be defined as an atom or group of atoms or reactive part which is responsible for the characteristic properties of the compounds.

The chemical properties of organic compounds are determined by the functional groups while their physical properties are determined by the remaining part of the molecule.
1. Alcohols
Alcohols are carbon compounds containing –OH group attached to alkyl group. The general formula of alcohol is R-OH where ‘R’ is an alkyl group and –OH is the functional group.
The IUPAC name of alcohol is derived by replacing –e, in the word alkane, by the suffix –ol. Hence we get the name alkanol.

Molecular formula
Common name
IUPAC name
Methyl alcohol
Ethyl alcohol
n-Propyl alcohol
Isopropyl alcohol or secondary propyl alcohol
n-Butyl alcohol
Isobutyl alcohol

Note: Alcohols are the simplest compounds, which contain carbon, hydrogen and oxygen. An alcohol may be defined as follows:
An organic compound in which a hydroxyl ( - OH) group is attached to an alkyl group ( R ) is called an alcohol. If R is an alkyl group, then the corresponding alcohol is described by the formula ROH.  The functional group in alcohols is hydroxyl group ( - OH). The –OH group in alcohols is also called alcoholic group.
Examples: - Methyl alcohol (CH3OH) and ethyl alcohol (C2H5OH0 are the simplest alcohols. An alcohol may  also be considered as a hydroxy derivative of an alkane. So, an alcohol can be obtained by replacing a
hydrogen atom of an alkane by a hydroxyl (-OH) group. Thus,
Alkane – H + OH  -------------> Alcohol
Or RH – H + OH-------------> ROH
Or, CnH2n+2  – H + OH ------------->CnH2n+1 OH
Therefore, simple alcohols can be described by the general formula CnH2n+1OH. For example, when a
hydrogen atom of methane is replaced by –OH group, methyl alcohol is obtained.
CH4 – H + OH -------------> CH3OH
Methane                                  Methyl alcohol
Similarly, from ethane one gets ethyl alcohol.
C2H6 – H + OH -------------> C2H5OH
Ethane                                        Ethyl alcohol
Naming alcohols: -
Like hydrocarbons, alcohols are also known by their common and IUPAC names. The naming of alcohols is
described below:
1. Common names of alcohols: - The common name of an alcohol is obtained by adding the term alcohol to
the name of the alkyl group.
Common name of an alcohol = name of the alkyl group + alcohol
Name of the alkyl group is derived from the number of carbon atoms in the carbon chain attached to the
– OH group. For example, C2H5OH is made of two parts as C2H5 and OH. C2H5 contains two carbon atoms. So, C2H5 is ethyl group (from ethane). So, Common name of C2H5OH = Ethyl + alcohol = Ethyl alcohol
2. IUPAC names of alcohols: - In IUPAC system, an alcohol is named as alkanol. The IUPAC name of an
alcohol is obtained as follows:
a) Count the number of carbon atoms in the continuous longest chain containing the –OH group.
b) From the number of carbon atoms in the longest chain, identify the parent alkane as done for hydrocarbons.
c) Name of the alcohol is then written by replacing ‘e’ of the parent alkane by –ol, i.e.
IUPAC name of an alcohol = IUPAC name of the parent alkane – e + ol

The method of naming alcohols is illustrated below:

a) CH3OH: - The molecule CH3OH contains a carbon chain containing only one carbon atom. Therefore, the parent alkane is methane. So,
IUPAC name of CH3OH = Methane – e + ol = Methanol CH3OH contains methyl (CH3) group. So,  Common name of CH3OH = Methyl + alcohol = Methyl alcohol 

Naming the alcohol 3CH3 – 2CH2 – 1CH2 – OH
In this molecule, the – OH group is present on carbon atom number 1. So,
IUPAC name of 3CH3 – 2CH2 – 1CH2OH = 1 – Propane – e + ol = 1 – propanol
The compound CH3 – CH2 – CH2OH contains n – propyl group (CH3 – CH2 – CH2 –). 
So, Common name of CH3 – CH2 – CH2OH = n-propyl alcohol
Physical properties of alcohols: 
Some common general physical properties of alcohols are given below:

a) Physical state and adour: - Most common alcohols are colourless liquid. Alcohols containing more than 10 carbon atoms in their molecules are solids. Lower alcohols have a characteristic odour and burning taste.

b) Solubility: - Lower alcohols such as methyl alcohol, ethyl alcohol are soluble in water in all properties. Solubility of alcohols in water decreases with an increase in the number of carbon atoms in the molecule. 

c) Conductivity: - Alcohols do not conduct electricity. This is because alcohols are covalent compounds.

d) Action of litmus: - Alcohols have no effect on litmus, i.e., alcohols do not change the colour of litmus. This is because alcohols are neutral compounds.
e) Boiling points: - The boiling points of alcohols increase with an increase in their molecular masses, thus, an alcohol containing larger number of carbon atoms in its molecule has higher boiling point than alcohol containing lesser number of carbon atoms.
Alcohol                         Methanol              Ethanol           Propanol            Butanol
Molecular mass:              32                         46                      60                   74

Boiling point                    64C                     78.10C           97.40C              117.40C

2. Aldehydes

Aldehydes are carbon compounds containing -CHO group attached to alkylgroup or hydrogen atom. The general formula of aldehydes is R – CHO where ‘R’ is an alkyl group or hydrogen atom and – CHO is the functional group. The IUPAC name of aldehyde is derived by replacing –e, in the word alkane, by the suffix –al. Hence we get the name “alkanal”.

Molecular formula
Common name
IUPAC name

3. Ketones

Ketones are carbon compounds containing carbonyl – CO – group attached to two alkyl groups. The general formula of ketone is R-CO-R’ where R and R’ are alkyl groups and – CO – is the functional group. The IUPAC name of ketone is derived by replacing –e, in the word alkane, by the suffix -one. Hence we get the name “alkanone”.

Molecular formula
Common name
IUPAC name
Dimethyl ketone (Acetone)
Ethyl methyl ketone
Diethyl ketone

4. Carboxylic Acids

Carboxylic acids are carbon compounds containing –COOH group attached to a hydrogen atom or alkyl group. The general formula of acid is R-COOH where ‘R’ is a hydrogen atom or alkyl group and –COOH is the functional group. The IUPAC name of acid is derived by replacing – e, in the word alkane, by the suffix –oic acid. Hence we get the name “alkanoic acid”.

Molecular formula
Common name
IUPAC name
Formic acid
Methanoic acid
Acetic acid
Ethanoic acid
Propionic acid
Propanoic acid
n-Butyric acid
Butanoic acid

The organic compounds containing the functional group – COOR in their molecules are called esters. Esters are described by a general formula
R – C – OR 
Where R and R may be same or different alkyl groups.

Physical properties of esters: -
Some general properties of esters are given below:

a) Physical state, colour and odour: - Lower esters are colourless volatile liquids, having pleasant odour
i.e. they have fruity smell. Higher esters are colourless, wax-like solids.

b) Solubility: - Lower esters are soluble in water. The solubility, however, decreases sharply with an increase in the molecular mass of the esters. All esters are soluble in organic solvents such as alcohol, benzene etc.

c) Boiling points: - Boiling points of esters are lower than those of the corresponding acids. This is because esters do not show hydrogen bonding whereas acids do.

Uses of esters: -Some common uses of esters are given below:
a) Esters are used as solvents for oils, gums, resins etc.
b) Esters are used as plasticisers for resins and plastics.
c) Esters are used as flavoring agent in cold drinks, ice creams, sweets etc.


1. Ethanol (C2H5OH)

Ethanol or ethyl alcohol or simply alcohol is one of the most important members of the family of alcohols.

Physical properties

(i) Ethanol is a clear liquid with burning taste.
(ii) Its boiling point is 351K which is higher than corresponding alkane.
(iii) It is completely miscible with water in all proportions.

Chemical properties

(i) Dehydration

(a) Intra molecular dehydration :

Ethanol, when heated with excess conc. H2SO4 at 443 K undergoes intra molecular dehydration (i.e. removal of water within a molecule of ethanol).

CH3CH2OH -------Conc.H2SO4/443K-----> CH2 = CH2 +H2O

(b) Inter molecular dehydration : 

When excess of alcohol is heated with conc. H2SO4
at 413K two molecules condense by losing a molecule of water to form ether (i.e. removal of water from two molecules of ethanol).

C2H5- OH + HO- C2H5 -------Conc.H2SO4/413K----> C2H5-O-C2H5 (Diethyl ether)+H2O

(ii) Reaction with sodium : 

Ethanol reacts with sodium metal to form sodium ethoxide and hydrogen gas.

2C2H5OH + 2Na ------------>   2C2H5ONa (sodium ethoxide)  + H2 ↑

(iii) Oxidation:  

Ethanol is oxidized to ethanoic acid with alkaline KMnO4 or acidified K2Cr2O7

CH3CH2OH ----Oxidation--->  CH3COOH (Ethanoic acid) + H2O

During this reaction, orange colour of K2Cr2O7 changes to green. Therefore, this reaction can be used for the identification of alcohols.

(iv) Esterificaiton : 

Ethanol reacts with ethanoic acid in the presence of conc.H2SO4 (catalyst) to form ethyl ethanoate and water. The compound formed by the reaction of an alcohol with carboxylic acid is known as ester (fruity smelling compound) and the reaction is called esterification.

C2H5OH + CH3COOH ---conc.H2SO4----->  CH3COOC2H5 (Ethyl ethanoate) + H2O

(v) Dehydrogenation : 

When the vapour of ethanol is passed over reduced copper catalyst at 573 K, it is dehydrogenated to acetaldehyde.

CH3CH2OH -----------Cu/573K ------> CH3CHO (Acetadehyde) +H2
Ethanol is used
1. As an anti-freeze in automobile radiators.
2. As a preservative for biological specimen.
3. As an antiseptic to sterilize wounds in hospitals.
4. As a solvent for drugs, oils, fats, perfumes, dyes, etc.
5. In the preparation of methylated spirit (mixture of 95% of ethanol and 5% of methanol),rectified spirit (mixture of 95.5% of ethanol and 4.5% of water), power alcohol (mixture of petrol and ethanol) and denatured sprit (ethanol mixed with pyridine).
6. In cough and digestive syrups.

Evil effects of consuming alcohol

• If ethanol is consumed, it tends to slow down metabolism of our body and depresses the central nervous system.
• It causes mental depression and emotional disorder.
• It affects our health by causing ulcer, high blood pressure, cancer,brain and liver damage.
• Nearly 40% accidents are due to drunken drive.
• Unlike ethanol, intake of methanol in very small quantities can cause death.
• Methanol is oxidized to methanal (formaldehyde) in the liver and methanol reacts rapidly with the components of cells.
• Methanal causes the protoplasm to get coagulated, in the same way an egg is coagulated by cooking. Methanol also affects the optic nerve, causing blindness.

2. Ethanoic acid (CH3COOH)

Ethanoic acid is most commonly known as acetic acid and belongs to a group of acids called carboxylic acids. Acetic acid is present in many fruits and sour taste of fruits is because of this acid.

1. Preparation of Ethanoic acid

Ethanol on oxidation in the presence of alkaline potassium permanganate or acidified potassium dichromate gives ethanoic acid.

CH3CH2OH (Ethanol) ------ Oxidation ------>  CH3COOH (Ethanoic acid) + H2O

2. Physical properties

(i) Ethanoic acid is a colourless liquid and has a sour taste.
(ii) It is miscible with water in all proportions.
(iii) Boiling point (391 K) is higher than corresponding alcohols, aldehydes and ketones.
(iv) On cooling, pure ethanoic acid is frozen to form ice like flakes. They look like glaciers, so it is called glacial acetic acid.

3. Chemical properties

(i) Ethanoic acid is a weak acid but it turns blue litmus to red.

(ii) Reaction with metal

Ethanoic acid reacts with metals like Na, K, Zn, etc to form metal ethanoate and hydrogen gas.

2CH3COOH + Zn      -------------->  (CH3COO)2 Zn + H2 ↑
2CH3COOH + 2Na   ----------------> 2CH3COONa + H2 ↑

(iii) Reaction with carbonates and bicarbonates.

Ethanoic acid reacts with carbonates and bicarbonates and produces brisk effervescence due to the evolution of carbon dioxide.
2CH3COOH + Na2CO3 ------------> 2CH3COONa + CO2 ↑ + H2O
CH3COOH + NaHCO3 -------------> CH3COONa + CO2 ↑ + H2O

(iv) Reaction with base

Ethanoic acid reacts with sodium hydroxide to form sodium ethanoate and water
CH3COOH + NaOH ------------>  CH3COONa + H2O

(v) Decarboxylation (Removal of CO2)

When sodium salt of ethanoic acid is heated with soda lime (Solid mixure of 3 parts of NaOH and 1 part of CaO) methane gas is formed

CH3COONa ------NaOH / CaO------->  CH4 ↑ + Na2CO3

Ethanoic acid is used

1. For making vinegar which is used as a preservative in food and fruit juices.
2. As a laboratory reagent.
3. For coagulating rubber from latex.
4. In the preparation of dyes, perfumes and medicine.

Links For   CBSE Class X Science Term-II

Question: Why does Ethanoic acid called glacial acetic acid? (Imp.)

Ans.  On cooling, pure ethanoic acid is frozen to form ice like flakes. They look like glaciers, so it is called glacial acetic acid.

Question: Why is the conversion of ethanol to ethanoic acid an oxidation reaction? (Imp.)

Ans. When ethanol is oxidised, hydrogen is removed from its molecule and oxygen is added so as to form ethanoic acid. Thus, conversion of ethanol into acetic acid is an oxidation reaction.

Question:  A mixture of ethyne and oxygen is burnt for welding. Can you tell why a mixture of ethyne and air is not used? (Imp.)

Ans. Ethyne has only two hydrogen atoms and two carbon atoms in its molecule. It burns in air with a sooty flame, because the oxygen from air is insufficient to burn the carbon completely. Thus, pure oxygen is used which completely burns carbon and hydrogen and produces a very hot flame.

Question:  Why is the conversion of ethanol to ethanoic acid considered an oxidation reaction?

Ans. Conversion of ethanol to ethanoic acid is considered an oxidation reaction since it involves:
(i) addition of oxygen to the ethanol molecule (ii) removal of hydrogen from the ethanol
molecule             .Carbon and Its Compounds

1 comment:

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