Class X CH – 4 Carbon and its Compound
Syllabus of Carbon compounds: Covalent bonding in carbon compounds. Versatile
nature of carbon. Homologous series Nomenclature of carbon compounds containing functional groups (halogens, alcohol, ketones, aldehydes,
alkanes, and alkynes), the difference between saturated hydrocarbons and unsaturated hydrocarbons. Chemical properties of carbon compounds (combustion,
oxidation, and addition and substitution reaction). Ethanol and Ethanoic acid
(only properties and uses), soaps and detergents.
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1.
1. Carbon - Carbon means coal is a versatile element that forms the basis for all living organisms
and many of the things we use.
2. The
unique or versatile natures of carbon are catenation
and tetravalency.
3. Tetra valency
- Carbon has 4 valence electrons. This large variety of compounds is formed by carbon because of its
tetravalency and the property of catenation that it exhibits.
4. Carbon forms covalent bond –
Reasons are:
(i) Carbon could gain four electrons forming C4– anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons, that is, four extra electrons.
(ii) Carbon could lose four electrons forming C4+ cation. But it would require a large amount of energy to remove four electrons leaving behind a carbon cation with six protons in its nucleus holding on to just two electrons.
Carbon overcomes this problem by sharing its valence electrons with other atoms of carbon or with atoms of other elements.
5. Covalent bonds – Bonds which are formed by the sharing of electrons between two atoms so that both can achieve a completely filled outermost shell is called a covalent bond.
6. Types of bond :
(i) Non-polar covalent bond – Bond formed between two atoms of the same element of the same electronegativity. Ex – C –C, C=C, C = C etc.
(ii) Polar covalent bond - – Bond formed between two atoms of different elements of different electronegativity. Ex – C – H etc.
Carbon
forms covalent bonds with itself and other elements such as hydrogen, oxygen,
sulfur, nitrogen, and chlorine.
7. Propertiesof Covalent bond -
i. Covalent compounds have low melting
and boiling point - Covalently bonded molecules are seen
to have strong bonds within the molecule, but intermolecular forces are small.
This gives rise to the low melting and boiling points of these compounds.
ii. Covalent compounds are generally poor conductors of electricity-Since the electrons are shared between atoms of the covalent compound and no charged particles are formed, such covalent compounds are generally poor conductors of electricity.
8. Allotropes of carbon- Different forms of carbon which have different physical and same chemical properties are called allotropes of carbon and they are diamond, graphite, and fullerene (C60)
Diamond is the hardest nonmetal element and has a very high melting and billing point, due to the small atomic size in which force of attraction between molecules’ is very strong.
Graphite is a good conductor nonmetal element due to the presence of free electrons.
9. Organic Compound -Compounds
which were initially extracted from natural substances and could only be formed
within a living system, called Organic compound.
10. Vital force-
It was thought that carbon compounds or organic compounds could only be formed
within a living system. That is, it was postulated that a force was necessary
for their synthesis. This force was called Vital force Friedrich Wohler
disproved this in 1828 by preparing urea from ammonium cyanate.
11. Saturated hydrocarbons -The carbon compound whose valencies of all the atoms are satisfied by single bonds between them are called saturated compounds. These compounds are normally not very reactive.
Ex - Methane (CH4), Ethane (C2H6).
12. Unsaturated hydrocarbons -The carbon compound whose valencies of the atoms are satisfied by double bonds or triple bonds between them are known as unsaturated carbon compounds and they are more reactive than the saturated carbon compounds.
Ex - Ethene (C2H4), Propene (C3H6).
Carbon forms compounds containing double and triple bonds between carbon atoms. These carbon chains may be in the form of straight chains, branched chains or rings.
13. Saturated hydrocarbons generally give a clean flame while unsaturated carbon
compounds will give a yellow flame with lots of black smoke. Unsaturated hydrocarbons contain a greater proportion of
carbon than saturated hydrocarbon, so all the carbon particles do not get
oxidized. Due to incomplete combustion unsaturated carbon compounds give sooty flame and saturated
hydrocarbons give clean flame due to complete combustion.
14. Sooty
deposit on the metal plate - It is due to limiting the supply of air results in incomplete combustion of even
saturated hydrocarbons giving a sooty flame. The gas/kerosene stove
used at home has inlets for air so that a sufficiently oxygen-rich mixture is
burnt to give a clean blue flame.
15. Homologous series - A series of compounds in which the same structure and same functional group substitutes for hydrogen in a carbon chain, is called a homologous series. In homologous series, successive compounds differ by CH2 and having different chemical properties.
The ability of carbon to form chains gives rise to a homologous series of compounds in which the same functional group is attached to carbon chains of different lengths.
Ex.
Methane - CH4 Ethane - C2H6, Propane - C 3 H 8, Butane -C4 H10, etc.
Conversion of alcohol to carboxylic acids -
2C2H5OH + (KMnO4)→2CH3COOH + H2
Ethanal Ethanoic acid
Alkaline potassium permanganate or acidified potassium dichromate are oxidizing agents.
16. Combustion of Carbon – All carbon compound burns in oxygen to give carbon dioxide along with the release of heat and light.
(i) C + O2 → CO2 + heat and light
(ii) CH4 + O2 → CO2 + H2O + heat and light
(iii) CH3CH2OH + O2 → CO2 + H2O + heat and light.
17. Addition reaction- Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons. This phenomenon is called an addition reaction.
C2H4 + H2 = C2H6
Ethene Ethane
This reaction is commonly used in the hydrogenation of vegetable oils.
18. Substitution reaction - Saturated hydrocarbons are fairly unreactive and are inert in the presence of most reagents. However, in the presence of sunlight, chlorine is added to hydrocarbons in a very fast reaction. Chlorine can replace the hydrogen atoms one by one. It is called a substitution reaction.
CH4 + Cl2 = CH3Cl + HCl
(in the presence of sunlight).
19. Properties of Ethanol - Ethanol is a liquid at room temperature.
i. It is commonly called alcohol and is the active ingredient of all alcoholic drinks.
ii. It is a good solvent,
iii. It is also used in medicines such as tincture iodine, cough syrups, and many tonics.
iv. Ethanol is also soluble in water in all proportions.
v. Consumption of small quantities of dilute ethanol causes drunkenness. The intake of even a small quantity of pure ethanol can be lethal. Also, long-term consumption of alcohol leads to many health problems. Reactions of Ethanol.
20. Chemical properties of Ethanol –
(i) Reaction with sodium
2Na + 2CH3CH2OH → 2CH3CH2O– Na+ + H2
(Sodium ethoxide)
Alcohols react with sodium leading to the evolution of hydrogen. With ethanol, the other product is sodium ethoxide.
(ii) Heating of ethanol with an excess of sulphuric acid at 443 K gives ethene.
C2H5OH ------------ ➝ CH2= CH2 + H2O
170o
The
functional groups such as alcohols, aldehydes, ketones, and carboxylic acids show characteristic properties to the carbon compounds that contain them.
The action of soaps and detergents is based on the presence of both hydrophobic and
hydrophilic groups in the molecule and this helps to emulsify the oily dirt and
hence its removal.
21. Properties of ethanoic Acid –
(i) Ethanoic acid is commonly called acetic acid and belongs to a group of acids called carboxylic acids.
(ii) 5-8% solution of acetic acid in water is called vinegar and is used widely as a preservative in pickles.
(iii) The melting point of pure ethanoic acid is 290 K and hence it often freezes during winter in cold climates. This gave rise to its name glacial acetic acid.
(iv) Carboxylic acids are weak acids.
(i) Ethanoic acid is commonly called acetic acid and belongs to a group of acids called carboxylic acids.
(ii) 5-8% solution of acetic acid in water is called vinegar and is used widely as a preservative in pickles.
(iii) The melting point of pure ethanoic acid is 290 K and hence it often freezes during winter in cold climates. This gave rise to its name glacial acetic acid.
(iv) Carboxylic acids are weak acids.
22. Chemical properties of ethanoic acid -
(i) The reaction of ethanoic acid with alcohol - Ethanoic acid reacts with absolute ethanol in the presence of an acid catalyst to give an ester
CH3COOH + C2H5OH➝ CH3COOC2H5 + H2O in the presence of acid.
Ethanoic acid Ethanol Ester Water
(ii) Reaction of ethanoic acid with a base: Ethanoic acid reacts with a base such as sodium hydroxide to give a salt sodium ethanoate or commonly called sodium acetate and water:
NaOH + CH3COOH → CH3COONa + H2O.
(iii) Reaction with carbonates and hydrogen carbonates: Ethanoic acid reacts with carbonates and hydrogen carbonates to give rise to a salt, carbon dioxide, and water. The salt produced is commonly called sodium acetate.
2C H3COOH + Na2CO3 → 2CH3COONa + H2O + CO2
CH3COOH + NaHCO3 → CH3COONa + H2O + CO2
23. Esterification reaction: Esters are most commonly formed by the reaction of an acid and an alcohol. Ethanoic acid reacts with ethanol in the presence of an acid catalyst to give an ester –
CH3COOH + C2H5OH➝ CH3COOC2H5 + H2O in the presence of acid.
Ethanoic acid Ethanol Ester Water
Esters are sweet-smelling substances. These are used in making perfumes and as flavoring agents.
24. Saponification-
Esters react in the presence of an acid or a base to give alcohol and
carboxylic acid. Carboxylic acid reacts with a base such as sodium hydroxide to
give a salt (sodium ethanoate or commonly called sodium acetate) and water.
This reaction is known as saponification because it is used in the preparation
of soap.
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