carbon and its compounds

facts about carbon

facts about carbon

• it is a non-metal

• all living things are made up of carbon based compounds

• the amount carbon present in the earths crust and atmosphere is very small (0.02%)

• its presence can be tested by burning it in air to give CO2 which turns lime water milky

why carbon only forms covalent bonds

carbon has 4 valence electrons (tetravalent), and due to energy considerations, it is not possible to give or take 4 electrons. hence, to achieve inert configuration, it can only share electrons

self-combination of carbon

• carbon has a unique ability to combine with itself, atom to atom, to form long chains which gives rise to a large number of carbon compounds

• the bonds formed are very strong due to the fact that carbon atoms are small in size, which allows the nuclei to hold the shared electrons strongly

occurrence of carbon

carbon can occur in nature in both free state (allotropes) as well as combined state (as compounds)

the allotropes of carbon are; diamond, graphite and buckminsterfullerene

properties of diamond

• heavy and hard

• does not conduct electricity

• burns on strong heating to form carbon dioxide

properties of graphite

• light, soft and slippery to touch

• conducts electricity (due to presence of free electrons)

• burns on strong heating to form carbon dioxide

structure of diamond

• it is a giant molecule of carbon atoms

• each carbon atom is linked to four other carbon atoms by strong covalent bonds

• the rigid structure of diamond is what makes it very hard

structure of graphite

• it consists of layers of carbon atoms

• each carbon atom is joined to 3 other carbon atoms by strong covalent bonds to form hexagonal rings

• the layers are very far apart so there are no covalent bonds between them. instead, it is held together by a weak force of attraction called Van der Waals forces

• due to this sheet-like structure, graphite is very soft and slippery

uses of diamond

• used in cutting instruments like glass cutters due to its hardness

• used for making jewellery due to its brilliance

uses of graphite

• used as lubricant for fast moving parts of machinery due to its softness and high melting point

• used for making electrodes in dry cell due to its good conduction of electricity

• used for making pencil leads and black paint

structure of buckminsterfullerene

• its structure consists of clusters of 60 carbon atoms joined together to form spherical molecules

• it is football-shaped

• there are 20 hexagons and 12 pentagons of carbon atoms in each molecule

• it is a dark solid

properties of organic compounds

• they are covalent

• they have low MP and BP

• they are non-conductors of electricity

• they occur in all living things

how the vital force theory was disproved

earlier, people believed that organic compounds could only be formed within a living body. however, this was disproved by wohler when he prepared urea from ammonium cyanate

reasons for the large number of organic compounds

• catenation (self-linking): the ability of carbon to link with itself to form long chains gives rise to a large number of organic compounds. there are three types of chains; straight, branched and closed

• tetravalency: carbons valency is 4, which allows it to combine with many different atoms

hydrocarbons

• compounds made up of hydrogen and carbon only are called hydrocarbons

• the most important source of hydrocarbons is crude oil

• there are two types of hydrocarbons; saturated and unsaturated

saturated hydrocarbons

• hydrocarbons in which the atoms are connected only by single bonds are called saturated hydrocarbons

• they are also called alkanes

• they are not very reactive

• general formula for alkanes: CnH2n+2

unsaturated hydrocarbons

• a hydrocarbon in which two carbon atoms are connected by a double bond (alkene) or triple bond (alkyne) is called an unsaturated hydrocarbon

• they are quite reactive

• general formula of alkene: CnH2n

• general formula of alkyne: CnH2n-2

alkyl groups

• the groups formed by the removal of one hydrogen atom from an alkane molecule is called an alkyl group

• two main alkyl groups are —CH3 (methyl group) and —C2H5 (ethyl group)

• they are usually denoted by the letter —R

• general formula: CnH2n+1

cyclic hydrocarbons

• they are hydrocarbons in closed chains

• they can be saturated or unsaturated

• saturated examples: cyclohexane (C6H12), cyclobutane (C4H8)

• unsaturated examples: benzene (C6H6) [alternating double bonds]. they are also called aromatic compounds

IUPAC and common naming for straight-chain hydrocarbons

• stem word: number of carbon atoms- meth/eth/prop/but etc.

• suffix: type of bond- ane/ene/yne

• common naming for alkane 4 & beyond: n-(IUPAC name)

• common naming for alkenes: meth/eth/prop + ylene

• common naming for alkynes: acetylene, methyl-acetylene

IUPAC and common naming for branched-chain saturated hydrocarbons

• the longest chain of carbons is found first: meth/eth/prop etc.

• identify the side chains alkyl group as either methyl or ethyl

• find the position of the alkyl group and number it such a way that it gets the smallest number

• example: 2-methylpropane

• common names: iso-(total number of hydrocarbons name meth/eth/prop etc.)

isomers

• isomers are organic compounds having the same molecular formula but different structural formulla

• this is due to the different arrangements of carbon atoms in them

• examples: n-butane and iso-butane

• it is only possible in hydrocarbons having 4 or more carbon atoms

homologous series and their characteristics

• a homologous series is a group of organic compounds having similar structures and chemical properties in which the successive compounds differ by —CH2 group

• all members of a series can be represented by the same general formula

• any two adjacent homologues differ by 1 carbon atom and 2 hydrogen atoms

• any two adjacent homologues differ in molecular masses by 14u

• examples: alkanes, alkenes, alkynes, carboxylic acid etc.

heteroatom

in an organic compound, any atom other than carbon and hydrogen is called a heteroatom. the two heteroatoms being studied are halogen atoms and oxygen atoms

functional groups

an atom or group of atoms which makes a carbon compound reactive and decides its properties is called a functional group. some functional groups are;

• halo group: —X (Cl, Br, I)

• alcohol: —OH

• aldehyde: —CHO

• ketone: —CO—

• carboxylic acid: —COOH

haloalkanes

• when one hydrogen atom of an alkane is replaced by a halogen atom, we get haloalkane

• general formula: CnH2n+1X

• example CH3Cl (chloromethane OR methyl chloride), C3H7Cl (chloropropane OR propyl chloride)

alcohols

• the hydroxyl group (—OH) attached to a carbon atom of an alkane gives an alcohol

• general formula: CnH2+1OH

• examples: CH3OH (methanol OR methyl alcohol), C2H5OH (ethanol OR ethyl alcohol)

aldehydes

• the aldehyde group (—CHO) attached to the end of a carbon chain of an alkane gives an aldehyde

• general formula: CnH2nO

• examples: HCHO (methanal OR formaldehyde), CH3CHO (ethanal or acetaldehyde)

ketones

• ketones are carbon compounds containing the —CO— ketone group

• they can only occur in the middle of a chain, so they have to have a minimum of 3 carbon atoms

• general formula: CnH2nO

• examples: CH3COCH3 (propanone OR acetone), CH3COCH2CH3 (butanone OR ethyl methyl ketone)

carboxylic acids

• organic compounds containing carboxylic acid group (—COOH) are called carboxylic acids

• general formula R—COOH

• examples: HCOOH (methanoic acid OR formic acid), CH3COOH (ethanoic acid OR acetic acid)

fuels

• a fuel is a material which has energy stored in it. when a fuel is burnt, the energy is released as heat

• most common fuels are either free carbon or carbon compound

C + O2 → CO2 + heat + light

formation of coal

coal was formed by the decomposition of large land plants and trees buried under the earth millions of years ago, due to earthquakes and volcanic eruptions. the pressure caused by the sand, clay, water resulted in the formation of coal

how petroleum was formed

petroleum was formed by the decomposition of the remains of extremely small plants and animals buried under the sea millions of years ago. when they died, they sank to the bottom of the sea and were covered by mud and sand. the pressure converted the fossils into petroleum oil

flame

• a flame is the region where combustion of substances takes place

• a flame is only produced when gaseous substances burn

• there are two types of flames: blue flame and yellow flame

blue flame

• when oxygen supply is sufficient, the fuel burns with a blue flame

• the flame does not give light and is non-luminous

• complete combustion takes place

yellow flame

• when the oxygen supply is insufficient, then fuels burn with yellow flame

• the yellow color is due to the glow of hot, unburnt carbon particles

• it is luminous

• the unburnt carbon particles leave the flame as soot and smoke

combustion reactions

• all hydrocarbons burn in oxygen to produce CO2, H2O and heat

• alkanes: since they have less % of carbon, the compound gets oxidised completely and undergoes complete combustion, burning with a blue flame

• alkenes and alkynes: since they have more % of carbon, the compound doesnt get oxidsed completely and undergoes partial combustion, burning with a yellow sooty flame

oxy-acetylene flame

it is a mixture of acetylene (ethyne) and pure oxygen, which burns completely with blue flame. it is extremely hot and is used for welding metals

disadvantages of incomplete combustion

• leads to unburnt carbon in the form of soot which pollutes the atmosphere

• produces an extremely poisonous gas called CO

• blocks chimneys

substitution reactions

• the reaction in which one or more hydrogen atom of a hydrocarbon is replaced by some other atom is called a substitution reaction

• it only occurs in alkanes

• CH4 + Cl2 →(sunlight) CH3Cl + HCl

• by supplying more chlorine, more hydrogen atoms can be replaced one by one to form dichloromethane and trichloromethane (which is also called chloroform and is used as anaesthetic)

addition reactions

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

• the addition of hydrogen to an unsaturated hydrocarbon to obtain a saturated hydrocarbon is called hydrogenation

• CH2=CH2 + H2 →(Ni catalyst + heat) CH3–CH3

hydrogenation of oils

the vegetable oils are unsaturated compounds containing double bonds. when they go through hydrogenation, they form saturated fats called vegetable ghee which are solid

these saturated fats are not good for health

how to differentiate between saturated and unsaturated compounds

unsaturated compounds can decolourise bromine water, a red-brown liquid while saturated compounds cannot

physical properties of ethanol

• colourless liquid with pleasant smell

• burning taste

• low BP

• lighter than water and soluble due to presence of —OH group

• no effect on litmus solution

combustion of ethanol

C2H5OH + O3 → CO2 + H2O + heat

it undergoes complete combustion and burns with blue flame, hence it is used in fuel for cars

production of ethanol

it is produced on a large scale from sugar cane crop

after crystallisation of sugar from concentrated sugarcane juice, a dark brown liquid called molasses is left behind

ethanol is formed by the fermentation of the cane sugar present in these molassess

oxidation of ethanol

CHCH2OH + 2[O] →(alk. KMnO4/ acid. K2Cr2O7) CH3COOH + H2O

the alkaline potassium permanganate or the acidified potassium dichromate acts as the oxidising agent

reaction of ethanol with sodium metal

C2H5OH + Na → C2H5ONa + H2

this reaction is used as a test for ethanol. all alcohols react with sodium metal

dehydration of ethanol

CH3CH2OH →(conc.H2SO4 ; 170C) CH2=CH2 + H2O

the concentrated sulphuric acid acts as dehydrating agent

reaction of ethanol and ethanoic acid

C2H5OH + CH3COOH →(conc.H2SO4) CH3COOC2H5 + H2O

this is also called esterification

tests for alcohol

• sodium metal test

• ester test

uses of ethanol

• manufacture of paints, medicines, perfumes, dyes

• used as a solvent

• used in alcoholic drinks

• used as an antisceptic

denatured alcohol

• it is ethyl alcohol which has been made unfit for drinking purposes by adding small amounts of poisonous substances like methanol, copper sulphate etc

• this is because the government supplies industries ethyl alcohol duty-free, and doesn’t want people to use it for commercial uses

physical properties of ethanoic acid

• colourless liquid with the smell and taste of vinegar

• high BP

• freezes to form colourless, ice-like solid called glacial acetic acid

• miscible with water

chemical properties of ethanoic acid

ethanoic acid is acidic in nature and shows all properties of an acid

hydrolysis of esters

CH3COOC2H5 + NaOh →(heat) CH3COONa + C2H5OH

this process is called saponification, and is used for making soaps

physical properties of ester

• volatile liquids

• sweet, fruity smell

• used to make perfumes, artificial flavors and essences

tests for carboxylic acids

• sodium bicarbonate test

• litmus test

• ester test

uses of ethanoic acid

• used as a food preservative (as vinegar)

• used to make acetone and esters

• used for making cellulose acetate, which is an important artificial fibre

detergents

any substance which has cleansing action in water is called a detergent. they are of two types;

• soapy detergents (soap)

• non-soapy detergents (synthetic detergents)

soap and its examples

a soap is the sodium/potassium salt of a long chain carboxylic acid which has cleansing properties in water. it is a salt of a strong base (NaOH) and a weak acid (carboxylic acid) two examples are;

• sodium stearate C17H35COO-Na+

• sodium palmitate C15H31COO-Na+

manufacture of soap

soap is made from animal fat or vegetable oils, which contain a long chain carboxylic acid and an alcohol called glycerol. a strong base like NaOH is added to it and heated to form the sodium salt (soap) and glycerol

fat/oil + NaOH →(heat) sodium salt (soap) + glycerol

this process is called saponification

why common salt is added in soap making

it is added to precipitate out all the soap from the aqueous solution. it does this by decreasing the solubility of the soap until it separates out of the solution

structure of a soap molecule

a soap molecule consists of two parts; a long hydrocarbon part and a short ionic part (—COO-Na+)

the hydrocarbon part is hydrophobic, that is, its insoluble in water but soluble in oil and grease. it attaches itself to the oil and grease. the ionic part is hydrophilic, that is, its soluble in water but insoluble in oil and grease. it attaches itself to the water particles

micelles

it is a spherical aggregate of soap molecules and a colloidal suspension formed in soap solutions

in a soap micelle, the hydrocarbon ends direct towards the centre while the ionic ends direct outwards (because the ionic charges are repelling against each other)

limitations of soaps

• if the water is hard (contains calcium/magnesium salts), then a lot of soap is wasted in reacting with the calcium and magnesium ions of hard water to form an insoluble precipitate called scum

• this scum sticks to the clothes being cleaned and interferes with the cleansing ability of the additional soap

• the formation of lather is necessary for removing dirt. soap forms lather easily with soft water, but not with hard water

• examples of hard water: well water, hand-pump ; soft water: distilled water (softest)

limitations of soaps

• if the water is hard (contains calcium/magnesium salts), then a lot of soap is wasted in reacting with the calcium and magnesium ions of hard water to form an insoluble precipitate called scum

• this scum sticks to the clothes being cleaned and interferes with the cleansing ability of the additional soap

• the formation of lather is necessary for removing dirt. soap forms lather easily with soft water, but not with hard water

• examples of hard water: well water, hand-pump ; soft water: distilled water (softest)

limitations of soaps

• if the water is hard (contains calcium/magnesium salts), then a lot of soap is wasted in reacting with the calcium and magnesium ions of hard water to form an insoluble precipitate called scum

• this scum sticks to the clothes being cleaned and interferes with the cleansing ability of the additional soap

• the formation of lather is necessary for removing dirt. soap forms lather easily with soft water, but not with hard water

• examples of hard water: well water, hand-pump ; soft water: distilled water (softest)

synthetic detergent

it is a sodium salt of a long chain benzene sulphonic acid/alkyl hydrogensulphate which has cleansing properties in water. it consists of a large hydrocarbon group and a small ionic group like sulphonate (SO3-Na+) or sulphate (SO4-Na+)

structure of a synthetic detergent molecule

it consists of two parts; a long hydrocarbon chain and a short ionic part (—SO3-Na+ or —SO4-Na+)

the long hydrocarbon part is hydrophobic, which means it is insoluble in water but soluble in oil. it attaches itself to the oil/grease particles present on the cloth. the short ionic part is hydrophilic, which means it is soluble in water but insoluble in oil. it attaches itself to the water molecules

advantages of synthetic detergent over soap

• unlike soaps, detergents do not react with calcium and magnesium salts to form scum. hence, they can be used even with hard water

• they have stronger cleansing action

• they are more soluble in water

NOTE: the only disadvantage is that detergents are non-biodegradable while soaps are biodegradable