Carbon and its compounds

State some important features of carbon

1. Carbon is a non-metal

2. Carbon always forms covalent bonds

3. The atomic number of carbon is 6 which means that a neutral atom of carbon contains 6 electrons. So, the electronic configuration of carbon is K 2 , L 4

4. Since one carbon atom requires 4 electrons to achieve the eight-electron inert gas structure, the valency of carbon is 4.That is, carbon is tetravalent.

State some characteristics of covalent compounds

1. Covalent compounds have low melting and low boiling points.

2. Covalent compounds are nonconductor of electricity

3. Covalent compounds are usually (but not always) insoluble in water.

4. Covalent compounds react slowly

5. Covalent compounds show isomerism

Why are covalent bonds formed by carbon atoms strong?

The covalent bonds between the various carbon atoms are very strong and do not break easily. Due to the small size of carbon atoms, their nuclei hold the shared pairs of electrons between atoms strongly, leading to the formation of strong covalent bonds.

Why does carbon form only covalent bonds?

Carbon has 4 valence electrons, so it requires four more electrons to attain inert gas configuration but it would be difficult for nucleus with six protons to hold on to ten electrons, therefore it cannot gain 4 electron. Also it cannot loose 4 electrons due to energy considerations. Thus carbon forms bonds only by sharing electrons i.e. by forming covalent bonds only.

Why is melting and boiling point of covalent compounds low?

Forces of attraction between the molecules of covalent compounds is not very strong. So it takes very less heat to overcome these forces, and thus the melting point and boiling point of covalent compounds is low.

Why are covalent compounds poor conductors of electricity?

Covalent compounds do not have any free ions to conduct electricity. Thus covalent compounds are poor conductors of electricity.

How does carbon occur in nature?

Carbon occurs in the free state (as an element) as well as in the combined state (as compounds of other elements) in nature.

1. In the free state, Carbon only occurs in the form of diamond and graphite.

2. In the combined state, carbon occurs in the form of compounds such as (i)

(i) In the form of carbon dioxide in air, carbonates such as limestone, marble and chalk, fossil fuels like petroleum, coal and natural gas, and as organic compounds like proteins carbohydrates and fats.

Explain structure of diamond

Each carbon atom in a diamond crystal is linked to four other carbon atoms by strong covalent bonds. The surrounding four atoms are at the four vertices of a regular tetrahedron. The rigid structure of diamond makes it a hard substance.

Explain structure of graphite

A graphite crystal consists of layer of carbon atoms or sheets of carbon atoms. Each carbon atoms in a graphite layer is joined to three other carbon atoms by strong covalent bonds to form flat hexagonal rings

Explain the reason for occurence of a large number of organic compounds.

The two characteristic properties of carbon element which lead to the formation of a very large number of organic compounds ( or carbon compounds) are : (i) catenation ( self- linking), and (ii) tetravalency ( four valency). The property of carbon element due to which its atoms can join with one another to form long carbon chains is called ‘catenation’ Due to its large valency of 4, a carbon atom can form covalent bonds with a number of carbon atoms as well as with a large number of other atoms such as hydrogen, oxygen, nitrogen, sulphur, chlorine, and many more atoms.

What are the three types of covalent bonds?

(i) Single covalent bond:- A bond formed when a pair of electron is shared between two atoms. (ii) Double covalent bond :- A bond formed when two pairs of electrons are shared between two atoms. (iii) Tripple covalent bond :- A bond formed when three pairs of electrons are shared between two atoms.

What are hydrocarbons?

A compound made up of hydrogen and carbon only is called hydrocarbon Hydrocarbons are of two types: Saturated hydrocarbons and Unsaturated hydrocarbons.

What are saturated hydrocarbons?

A hydrocarbon in which the carbon atoms are connected by only single bonds is called a saturated hydrocarbon. Saturated hydrocarbons are also called alkanes. The general formula of saturated hydrocarbons or alkanes is CnH2n + 2 where n is the number of carbon atoms in one molecule of the alkane.

What are unsaturated hydrocarbons?

A hydrocarbon in which the two carbon atoms are connected by a ‘ double bond’ or a ‘triple bond’ is called an unsaturated hydrocarbon. Unsaturated hydrocarbons are of two types : (i) those containing carbon-carbon double bonds (alkenes), and (ii) those containing carbon-carbon triple bonds (alkynes)

What are alkenes?

An unsaturated hydrocarbon in which the two carbon atoms are connected by a double bond is called an alkene. The general formula of an alkene is Cn H2n where n is the number of carbon atoms in its one molecule.

What are alkynes?

An unsaturated hydrocarbon in which the two carbon atoms are connected by a triple bond is called an alkyne. The general formula of alkynes is CnH2n-2 where n is the number of carbon atoms is one molecule of the alkyne.

What is isomerism?

The organic compounds having the same molecular formula but different structure are known as isomers. Isomerism is possible only with hydrocarbons having 4 or more carbon atoms.

What is a heteroatom?

The element replacing hydrogen from hydrocarbon to confer specific properties to the compound is called hetroatom.

What is a homologous series?

A homologous series is a group of organised compounds having similar structures and similar chemical properties in which the successive compounds differ by CH2 group.

State the characteristics of homologous series

1. All the member of a homologous series can be represented by the same general formula. 2. Any two adjacent homologues differ by 1 carbon atom and 2 hydrogen atoms in their molecular formulae. 3. The difference in the molecular masses of any two adjacent homologues is 14 u. 4. All the compounds of a homologous series show similar chemical properties. 5. The members of a homologous series show a gradual change in their physical properties with increase in molecular mass

What are functional groups?

An ‘atom’ or ‘a group of atoms’ which makes a carbon compound (or organic compound) reactive and decides its properties ( or functions) is called a functional group

How was coal formed?

Coal was formed by the decomposition of large land plants and trees buried under the earth millions of years ago.

How was petroleum formed?

Petroleum oil (and natural gas) were formed by the decomposition of the remains of extremely small plants and animal buried under the sea millions of years ago

Why do substances burn with a flame or without a flame?

A flame is produced only when gaseous substances burn. All the gaseous fuels burn with a flame but only those solid and liquid fuels which vaporize on heating (to form a gas), burn with a flame. For example, cooking gas (LPG) is a gaseous fuel which burns with a flame but wax and kerosene oil are solid and liquid fuels respectively, which vaporize (or form gas) on heating and hence burn with a flame.

1. When the oxygen supply (or air supply) is sufficient, then the fuels burn completely producing a blue flame.

2. when the oxygen supply (or air supply) is insufficient, then the fuels burn incompletely producing mainly a yellow flame

Those solid and liquid fuels which do not vaporize on heating, burn without producing a flame

What is combustion?

The process of burning of a carbon compound in air to give carbon dioxide, water, heat and light, is known as combustion.

Why do saturated hydrocarbons burn with a blue flame?

The saturated hydrocarbons (alkanes) generally burn in air with a blue, non- sooty flame. This is because the percentage of carbon in the saturated hydrocarbons is comparatively low which gets oxidized completely by the oxygen present in air.If

If the bottom of cooking utensils are getting blackened, what does it show?

If the bottom of the cooking utensils in our homes are getting blackened, it shows that the air holes of the gas stove (or kerosene stove) are getting blocked and the fuel is not burning completely (the fuel gets wasted in this case)

Why do unsaturated hydrocarbons burn with a yellow flame?

The unsaturated hydrocarbons (alkenes and alkynes) burn in air with a yellow, sooty flame (producing black smoke). For example, ethane and ethyne burn in air with a sooty flame. The unsaturated hydrocarbons ( alkenes and alkynes) burn with a sooty flame because the percentage of carbon in unsaturated hydrocarbons is comparatively higher 9than that of alkanes), which does not get oxidized completely in the oxygen of air.if unsaturated hydrocarbons are burned in pure oxygen, then they will burn completely producing a blue flame(without any smoke at all).

What are substitution reactions? How does it apply to saturated hydrocarbons? Give one example.

Saturated hydrocarbons ( alkanes) are quite unreactive (because they contain only carbon-carbon single bonds) being unreactive, saturated hydrocarbons do not react with many substance. Saturted hydrocarbons, however, undergo substitution reactions with cholrine in the presence of sunlight. The reaction in which one (or more) hydrogen atom of a hydrocarbon is replaced by some other atoms (like chlorine) is called a substitution reaction. Substitution reaction of methane with chlorine. Methane reacts with chlorine in the presence of sunlight to form chloromethane and hydrogen chloride.

What is an addition reaction?

The reaction in which an unsaturated hydrocarbon combines with another substance to give a single product is called an addition reaction.

What is hydrogenation? Give one application of it.

The addition of hydrogen to an unsaturated hydrocarbon to obtain a saturated hydrocarbon is called hydrogenation. The process of hydrogenation takes place in the presence of nickel or palladium metals as catalyst.the process of hydrogenation has an important industrial application : it is used to prepare vegetable ghee (or vanaspati ghee) from vegetable oils.

How do we chemically distinguish between cooking oil and butter?

We can distinguish chemically between a cooking oil and butter by the bromine water test. Add bromine water to a little of cooking oil and butter taken in separate test- tubes. (i) Cooking oil decolourises bromine water (showing that it is an unsaturated compound) (ii) Butter does not decolourise bromine water (showing that it is a saturated compound)

What is ethanol?

Ethanol is the second member of the homologous series of alcohols (the first member being methanol). The formula of ethanol is C2H5OH. The common name of ethanol is ethyl alcohol

State the physical properties of ethanol.

Ethanol is a colourless liquid having a pleasant smell and a burning taste. Ethanol is a volatile liquid having a low boiling point of 78C (351 K). it is lighter than water. Ethanol mixes with water in any proportion. It is a neutral compound

Combustion (with regard to ethanol)

Ethanol is a highly inflammable liquid. It cathes fire easily and starts burning. Ethanol burns readily in air with a blue flame to form carbon dioxide and water vapour, and releasing a lot of heat and light

Oxidation (with regard to ethanol)

‘Oxidation’ means ‘controlled combustion’ when ethanol is heated with alkaline potassium permanganate solution (or acidified potassium dichromate solution), it gets oxidized to ethanoic acid.

How is the presence of ethanol tested?

Ethanol reacts with sodium to form sodium ethoxide and hydrogen gas. This reaction is used as a test for ethanol

Dehydration (with regard to ethanol)

Dehydration of an alcohol means removal of water molecule from it. When ethanol is heated with excess of concentrated sulphuric acid at 1700 C (443 K), it gets dehydrated to form ethane (which is an unsaturated hydrocarbon

Formation of ester (reaction with ethanoic acid)

Ethanol reacts with ethanoic acid on warming in the presence of a few drops of concentrated sulphuric acid to form a sweet smelling ester, ethyl ethanoate The reaction in which a carboxylic acid combines with an alcohol to form an ester is called esterification. Esterification takes place in the presence of a catalyst like concentrated sulphuric acid.

Uses of ethanol

1. Ethyl alcohol (ethanol) is used in the manufacture of paints, varnishes, lacquers, medicines, perfumes, dyes, soaps and synthetic rubber.

2. Being a good solvent ethyl alcohol (ethanol) is used in medicines such as tincture iodine, cough syrups and many tonics.

3. Ethyl alcohol (ethanol) is used as a fuel in cars alongwith petrol. It is also used as a fuel in spirit lamps.

4. Ethyl alcohol (ethanol) is used in alcoholic drinks *beverages) like whisky, wine, beer and other liquors. Whisky contains about 35% of ethyl alcohol, wine contains 10% to 20% of ethyl alcohol, and beer contains about 6% of ethyl alcohol.

5. Ethyl alcohol (ethanol) is used as an antiseptic to sterilize wounds and syringes in hospitals and dispensaries.

What is denatured ethanol?

Denatured alcohol is ethyl alcohol which has been made unfit for dinking purposes by adding small amounts of poisonous substances like methanol, pyridine, copper sulphate, etc.

What is ethanoic acid?

The formula of ethanoic acid is CH3COOH. The common name of ethanoic acid is acetic acid. A dilute solution of ethanoic acid in water is called vinegar.Vinegar contains abount 5 to 8 per cent achanoic acid.

What are the physical properties of ethanoic acid?

1. Ethanoic acid is a colourless liquid having a sour taste and a smell of vinegar. 2. The boiling point of ethanoic acid is 1180 C (391 K) 3. When pure ethanoic acid is cooled, it freezes to form a colourless, ice-like solid (which looks like a glacier). Due to this, pure ethanoic acid is called glacial ethanoic acid (or glacial acetic acid) 4. Ehanoic acid is miscible with water in all proportions.

What is saponification?

The reaction in which an alkali solution reacts with the ester to form constituent alcohol and sodium salt of the acid is known as saponification.

What is the main use of ethanoic acid?

1. Dilute ethanoic acid (in the form of vinegar) is used as a food preservative in the preparation of pickles and sauces (like tomato sauce). As vinegar, it is also used as an appetiser for dressing food dishes.

What is a soap?

A soap is the sodium salt of long chain carboxylic acid (fatty acid) which has cleansing properties in water. A soap has a large non-ionic hydrocarbon group and an ionic group COONa+.

What is a detergent?

Detergents are sodium salts of sulphonic acids. The ionic group of detergent is SO-3Na+

What is the composition of a soap or detergent molecule?

Soap and detergent molecules consist of:

1. Hydrophobic tail: repels water, attracts oil

2. Hydrophillic ionic head: attracts water

What is a micelle?

The cluster of soap or detergent molecules when they are mixed in water is called a micelle. In this cluster, the hydrophobic tails of the molecules are facing inwards surrounding the oily dirt and the ionic heads are protuding outwards.

Differentiate between soaps and detergents

1. Sodium salts of the long chain carboxylic acids. The ionic group in soaps is – COO-Na+. Sodium salts of long chain sulphonic acids. The ionic group is – SO3-Na+.

2. Not suitable with hard water. Suitable even with hard water.

3. Prepared from animal fats or vegetable oils. Prepared from the hydrocarbons of petroleum.

4. Biodegradable. Non-biodegradable. 5. Weak cleansing action. Strong cleansing action.

Explain the cleansing action of soaps and detergents

The cleansing action of soaps and detergents follows the same principle. Soaps and detergents consists of a large hydrocarbon tail and a negatively charged head. The hydrocarbon tail is hydrophobic (i.e. it repels water) and negatively charged head is hydrophilic (i.e. it attracts water). When a soap or detergent is dissolved in water, the molecules gather together as clusters, called micelles. In cleansing, the hydrocarbon tail attaches itself to oily dirt. When water is agitated, the oily dirt tends to lift off from dirty surface and dissociates into fragments. The other tails stick to oil. The solution now contains small globules of oil surrounded by detergent molecules. The negatively charged heads present in water prevent the small globules from coming together and form aggregates and the cloth gets cleaned

Why are soaps ineffective cleansing agents in hard water?

Soaps are not effective cleansing agent in hard water because it reacts with metal ions such as Ca2+ and Mg2+ present in hard water to form insoluble precipitate (called scum).

Why are detergents effective cleansers in hard water?

Detergents do not give precipitate with metal ions and, therefore, is effective even with hard water.

How do synthetic detergents cause water pollution?

Some detergent are not broken down by micro-organisms present in lakes and rivers. Such detergents remain in water bodies for a long time and make water unfit for use by aquatic life. For eg : Phosphate salts present in detergents help in rapid growth of algae in water bodies leading to deoxygenation of water. Due to reduction of oxygen in water bodies, the aquatic animals like fish can die