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CARBON AND ITS COMPOUNDS Carbon Compounds The compounds of carbon are called carbon compounds. Carbon forms a large number of compounds. Today approximately 3 millions of carbon compounds containing a variety of other elements are known. Many of these carbon compounds are being used in our daily life e.g. soaps, detergents, fabrics, plastics, medicines, dyes and food preservators etc. Types Of Covalent Bonds 1. Single Covalent Bond 2. Double Covalent Bond 3. Triple Covalent Bond Existence Of Carbon The amount of carbon present in the earth crust and atmosphere is quite meager. The earth’s crust has 0.02 % carbon in the form of minerals like carbonates, bicarbonates, coal and petroleum. The atmosphere has 0.03 % of carbon in the form of carbon dioxide. 1. Single Covalent Bond When only one pair of electrons is shared between two combining atoms a single bond is formed. In this each atom shares one electron. A single bond is denoted by single dash(-) between the two atoms, e.g. H 2 , Cl 2 , H 2 O, NH 3 , CH 4 , CCl 4 etc. Types Of Carbon Compounds Carbon mainly forms two types of compounds: 1. Organic Compounds The compounds of carbon (except the oxides, carbonates, hydrogen carbonates and carbides of carbon) are called organic compounds. 2. Inorganic Compounds The oxides, carbonates, hydrogen carbonates and carbides of carbon are called inorganic carbon compounds. Hydrocarbons Compounds of carbon with hydrogen are called hydrocarbons. Bonding In Carbon- The Covalent Bond The atomic number of carbon is 6 and its electronic configuration is 2,4, i.e., it has four electrons in its outermost shell and needs to gain or loose four electrons to attain noble gas configuration. But it is not possible for carbon to gain or to loose four electrons. It is because: (i) If it gains four electrons forming C4- anion, it would be difficult for the nucleus with six protons to hold on to ten electrons, that is four extra electrons. (ii) If it looses four electrons forming C4+ cation, 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 its problem by sharing its valence electrons with other atoms of carbon or with other atoms of other elements. The shared electrons belong to the outer shells of both the atoms and lead to both atoms attaining the noble gas configuration. Covalent Bond A covalent bond is the bond between two atoms which is formed by the sharing of electrons between the two atoms. The sharing of electrons takes place in such a way that each atom in the resulting molecule gets the stable electron arrangement of an inert gas. When ever a non – metal reacts with another non – metal, sharing of electrons takes place between their atoms and a covalent bond is formed. Covalently bonded molecules are seen to have a strong bond within the molecule but intermolecular forces are small. This gives rise to low melting and boiling points of these compounds. And covalent compounds are generally poor conductors of electricity. Formation Of Cl 2 Molecule Chlorine is a monovalent atom. It has 7 electrons in the outermost shell and to become stable it needs one electron. Therefore two chlorine atoms share their electrons to form a diatomic molecule of chlorine Cl 2 . This allows each chlorine atom to attain noble gas configuration of argon. Other examples are: (i) HCl (Hydrogen chloride) (ii) H 2 O (Water) (iii) CH 4 (Methane) (iv) C 2 H 6 (Ethane) 2. Double Covalent Bond When two pairs of electrons are shared between two combining atoms, a double bond is formed. In a double bond each atom shares two electrons. A double bond is denoted by double dash (=) e.g. O 2 , CO 2 , C 2 H 4 Formation Of CO 2 Molecule Carbon is a tetravalent atom and oxygen is a divalent atom. Carbon needs four more electrons to achieve nearest noble gas configuration and oxygen needs two more electrons to achieve nearest noble gas configuration. So one carbon atom combines with two oxygen atoms and each oxygen atom shares two electrons with one carbon atom. Carbon shares its four electrons i.e., two electrons with each oxygen atom. The two electrons contributed by each oxygen element and four by carbon two with each oxygen gives rise to a pair of two shared pairs of electrons and hence a double bond is formed. Other examples are: (i) O 2 (Oxygen Molecule) (ii) C 2 H 4 Ethane 2. Triple Covalent Bond When three pairs of electrons are shared between two combining atoms, a triple bond is formed. In a triple bond each element shares three electrons. A triple bond is denoted by triple dash ( ≡ ) e.g. N 2 , C 2 H 2 . Formation of N2 molecule Nitrogen has the atomic number 7. It has five electrons in its outermost shell. In order to attain an octet each nitrogen atom in a molecule of nitrogen contributes three electrons giving rise to three shared pairs of electrons. This is said to constitute a triple bond between two nitrogen atoms. C 2 H 2 Ethene Hydrocarbons Compounds of carbon and hydrogen are called hydrocarbons. The hydrocarbons along with carbon and hydrogen may also include halogens, oxygen, sulphur and phosphorous etc.. Types Of Hydrocarbons 1. Saturated Hydrocarbons The hydrocarbons in which the carbon atoms are linked with a single bond are saturated hydrocarbons. To form these, the first step is to link the carbon atoms together with a single bond and then use the hydrogen atoms to satisfy the remaining valencies of carbon. The saturated hydrocarbons are generally called alkanes. Alkanes are solid at room temperature and the most stable hydrocarbons among all or we can say that these compounds are generally not very reactive. 2. Unsaturated Hydrocarbons The hydrocarbons in which the carbon atoms are linked with a double or triple bond are called unsaturated hydrocarbons. To form these, the first step is to link the carbon atoms together with a double or triple bond and then use the hydrogen atoms to satisfy the remaining valencies of carbon. The unsaturated hydrocarbons are generally called alkenes or alkynes. Alkenes and alkynes are unstable hydrocarbons and liquid at room temperature. The unsaturated hydrocarbons are reactive in nature. Homologous Series Of Hydrocarbons A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series. In a homologous series each successive member of the series differs with the previous member by a CH 2 group and 14 u by mass. 1. Catenation Carbon has the unique ability to form bonds with other atoms of carbon. This ability of self combination of carbon is called catenation. These compounds may have long chains of carbon, branched chains of carbon and or even carbon atoms arranged in the rings. In addition carbon atoms may be linked by single, double and triple bonds. Characteristic Of Homologous Series (i) All the members of homologous series can be represented by the same general formula. (ii) The molecular formulae of any two successive adjacent members of a homologous series differ by a CH 2 group. (iii) The molecular masses of any two successive members of a homologous series differ by 14 u. (iv) All the members of a homologous series have similar chemical properties. (v) All the members of a homologous series have the same functional group. (vi) The members of a homologous series show a gradation in the physical properties as the molecular mass increases. For example the melting and boiling points increases with the increase in the atomic mass. 2. Tetravalency Since carbon has a valency of four, it is capable of bonding with four other atoms of carbon or atoms of some other monovalent element. Writing Formulae Of Hydrocarbons (i) Chemical or molecular formula (ii) Condensed formula (iii) Structural formula Why The Covalent Compounds Formed By Carbon Are Stable As Compared To The Covalent Compounds Formed By Other Elements? Covalent compounds formed by carbon are stable in nature due to small size of the carbon atom. Due to this the nucleus has a strong hold on the shared pairs of electrons. Chemical Formula Or Molecular Formula The chemical or molecular formula consists of the total number of atoms of the elements present in the hydrocarbon. Versatile Nature Of Carbon Why Carbon Forms A Large Numbers Of Compounds? It is due to the versatile nature of carbon it can form large number of compounds. This versatile nature is due to two peculiar properties of carbon which are:- Example Methane CH 4 , Ethane C 2 H 6 , Propane C 3 H 6 Condensed Formula The condensed formula shows the total number of hydrogen atoms attached to each carbon atom in a compound. Example Ethane CH 3 CH 3 , Propane CH 3 CH 2 CH 3 Structures Of Hydrocarbons The hydrocarbons exist in the following structures: (i) Straight chain structures Propyne Butyne Ring Structures (ii) Ring or Cyclic structures Cyclopentane Cyclohexane (iii) Branched structures Benzene Nomenclature Of Carbon Compounds (i) (ii) (iii) (iv) (v) Identify the number of carbon atoms in carbon compound. Name the carbon compounds according to the number of carbon atoms and the type of bond present. If the structure has branched chain, identify the longest chain and then identify the number of carbon atoms and name it. Identify the longest chain. Then number the carbon atoms in such a fashion that the functional group; if any; would come at the lowest number. To identify the lowest number the numbering should be done from both sides of the parent chain. In case of a functional group present, write the prefix or suffix of the functional group accordingly. Then write the name of the parent compound. The number of the carbon atom to which the functional group or the branch is attached is to be written before the name of the parent chain with a hyphen in between. Straight Chain Structures (i) Alkanes Propane (vi) Branched Structures Isomers Isomers are the chemical compounds having same chemical or molecular formula but different structural formula. The isomers have different chemical properties. Alkanes (i) Isomers of Butane Butane 2- methyl propane (ii) Isomers Of Pentane Butane (ii) Alkenes Pentane Ethene (iii) Alkynes Butene 2- methyl butane 5. || Carboxylic Acid Group − COH or − CO − OH O || Ester Group − COOR or − C − OR 6. Halogen Group 4. − X (X can be Cl, Br or I) 1. Alcoholic Group – OH 2,2 – dimethyl propane Alkenes (i) Isomers of Butene 1-Butene 2-Butene The alcoholic group is made up of oxygen atom and hydrogen atom joined together. The alcoholic group is also known as alcohol or hydroxyl group. The compounds containing alcoholic group are known as alcohols. General Formula Of Alcohols R – OH Where R Alkyl Group –OH Functional Group Alcohols are derivatives of hydrocarbons in which hydrogen atoms in the parent hydrocarbon have been replaced by one or more hydroxyl groups (– OH). Homologous Series Of Alcohols Alcohols form homologous series. General Formula For Homologous Series Of Alcohols C n H 2n+1 – OH Where n is the number of carbon atoms in one molecule of alcohol. The first five members of the homologous series of alcohols are given below: - Alkynes (i) Isomers Of Butyne 1-Butyne Functional Groups 2-Butyne An atom or a group of atoms which makes a carbon compound reactive and decides its properties is called a functional group. Replacing part of a hydrocarbon with functional group changes the structure, properties and uses of a compound. Some of the important functional groups are as follows:1. Alcoholic Group − OH O || 2. Aldehydic Group − CHO or − C − H O || 3. Ketonic Group –C=O– or − C − or − CO − O O || || an aldehydic group is –C– H and a ketonic group is – C –. We can see that both aldehydes and ketones have a common O O || || –C – group. The –C – group, in general, is called a carbonyl group. O Common Name Methyl Alcohol IUPAC Name Methanol Alcohol Formula CH 3 OH Ethyl Alcohol Ethanol C 2 H 5 OH Propyl Alcohol Propanol C 3 H 7 OH Butyl Alcohol Butanol C 4 H 9 OH Nomenclature Of Alcohols IUPAC Method The last e of the parent alkane is replaced by ol to indicate the presence of – OH Group. Example (i) CH 3 OH Common Name: Methyl Alcohol IUPAC Name: Methanol As the parent contains one carbon atom so parent alkane is called methane. As it also contains hydroxyl group the last e of the alkane is replaced by ol forming methanol. In common name methyl followed by the word alcohol. Ethanol (Ethyl Alcohol) Chemical Formula – CH 3 CH 2 OH Or C 2 H 5 OH Ethanol is most common and most widely used alcohol. In some cases ethanol is just called alcohol. Physical Properties Of Ethanol 1. It is a colourless liquid having a pleasant smell and burning taste. 2. 3. 4. 5. 6. 7. Ethanol is a volatile liquid having a low boiling point of 780C. It is lighter than water and mixes in it in any proportion. Ethanol is a covalent compound not containing any ions. Ethanol containing 5 % water is called rectified spirit. Ethanol has no effect on any litmus solution. Ethanol does not conduct electricity. Chemical Properties Of Ethanol 1. Combustion Ethanol is highly inflammable liquid. It catches fire very easily and starts burning. Ethanol burns readily in air with a blue flame to form carbon dioxide and water vapour. Cumbustion C 2 H 5 OH + 3O 2 → 2CO 2 + 3H 2 O + energy A lot of heat is produced during this process. Note All alcohols like methanol, propanol etc. burn in air to form CO 2 and water and produce a lot of heat. 2. Reaction With Sodium Metal Ethanol reacts with sodium to form sodium ethoxide and hydrogen gas 2C 2 H 5 OH + 2Na → 2 C 2 H 5 ONa + H 2 Note: -This property shows the mild acidic nature of alcohol. This reaction is used as a test for ethanol. 3. Oxidation Oxidation means controlled combustion. Oxidation of ethanol is of two types. Strong Oxidation (Complete Oxidation) When ethanol is heated with alkaline potassium permanganate solution (an aqueous solution of potassium permanganate containing sodium hydroxide) its complete oxidation takes place and ethanoic acid is formed. Alkaline → CH 3 COOH + H 2 O CH 3 CH 2 OH + 2[O] This reaction can be carried out by adding 5 percent solution of potassium permanganate in sodium hydroxide solution to ethanol, drop wise till the purple colour of potassium permanganate solution no longer disappears. Actually the complete oxidation of alcohol occurs in two steps. CH 3 CH 2 OH + [O] Oxidation) CH 3 CHO + [O] → CH 3 CHO → CH 3 COOH + H2O (Mild (Strong Oxidation) Note All the alcohols form carboxylic acids on complete oxidation with strong oxidizing agents. 4. Reaction With Ethanoic Acid (Esterification) Ethanol reacts with ethanoic acid in the presence of a few drops of concentrated sulphuric acid to form sweet smelling ester. Conc. H2SO 4 CH 3 COOC 2 H 5 + H 2 O CH 3 COOH + C 2 H 5 OH Ethanoic Acid Note Ethanol Ester Ethyl Acetate All alcohols react with carboxylic acids to form sweet smelling esters in the presence of little amount of concentrated sulphuric acid. Uses Of Esters (i) Used in making perfumes. (ii) Used as flavouring substances. 5. Dehydration Of Ethanol This is a reaction to give unsaturated hydrocarbons. When ethanol is heated at 443 K with excess of concentrated sulphuric acid, it results in the dehydration of ethanol to give ethane – Hot conc. C2H4 + H2O C 2 H 5 OH → H2 SO 4 Ethanol Ethene Uses Of Ethanol 1. Used in the manufacture of paints, varnishes, lacquers, medicines, perfumes, dyes, soaps and synthetic rubber. 2. It is used in the preparation of organic compounds like ether, chloroform and iodoform. 3. It is used as liquid in alcohol thermometers and in spirit lamps. 4. It is used as fuel in internal combustion engines and as a substitute for petrol in motorcars as power alcohol. 5. It is used as an antiseptic to sterilize wounds and syringes in hospitals. 6. It is used in alcoholic drinks like whisky, wine, beer and other liquors. 7. Ethyl alcohol is used as a solvent. 8. Ethanol is used for making antifreeze mixtures, which are used in the radiators of motor vehicles in cold countries. Harmful Effects Of Alcohol 1. Alcohol is an intoxicant, so under the influence of alcohol a person looses his sense of discrimination. 2. Alcohol drinking ruins the health of a person concerned. It damages the liver and makes the brain dull. 3. The drinking of adulterated alcohol containing methyl alcohol causes severe poisoning leading to blindness and even death. 4. The alcohol drinking by the head of the family has a very bad effect on the psychological development of children. Denatured Alcohol It is the ethanol which has been made unfit for drinking purposes by adding poisonous substances like methanol, pyridine, copper sulphate etc. 2. Aldehydes – CHO O || Aldehydes are compounds containing carbonyl group, − C − group, so it is also known as carbonyl compound. The carbon atom of the carbonyl group has two free valencies (-C-) so two atoms or groups of atoms can be attached to the carbon atom of carbonyl group. In aldehydes, the carbon atom of carbonyl group is attached to one alkyl group and one hydrogen atom and is represented as follows: O || Or Or R − CHO RCHO R −C −H Like alcohols aldehydes are also the organic compounds which are made up of only carbon, hydrogen and oxygen elements. Homologous Series Of Aldehydes Aldehydes form the following homologous series. General Formula C n H 2n+1 CHO Where n is the number of carbon atoms. Nomenclature Of Aldehydes IUPAC Name The IUPAC name of an aldehyde is obtained from the parent alkane by replacing the last letter e with a suffix al. First five members of homologous series of aldehydes are:Common Name IUPAC Name Aldehyde Formula Formaldehyde Methanal HCHO Acetaldehyde Ethanal CH 3 CHO Propionaldehyde Propanal C 2 H 5 CHO Butyraldehyde Butanal C 3 H 7 CHO 3. Ketones – C O– Ketones are the carbon compounds having carbonyl group so it is called carbonyl compound. Ketones are the organic O || compounds containing Ketonic group – C – or – C O – . Ketonic group always occurs in the middle of a carbon chain and the simplest ketone must contain at least three carbon atoms in its molecule. There can be no ketone with less then 3 carbon atoms. Where R is an alkyl group. The members are: Common Name Formic Acid Acetic Acid Propionic Acid Butrylic Acid Valeric Acid Common Naming Alkyl groups are named first in increasing order and are followed by the word 'Ketone'. General Formula For Ketones C n H 2n O Where n is the number of carbon atoms. The first few members of homologous series of ketones are: Common Name IUPAC Chemical Name Formula Acetone, Propanone CH 3 COCH 3 Dimethyl Ketone Methyl Ethyl Butanone CH 3 CO C 2 H 5 Ketone Methyl Propyl Pentanone CH 3 CO C 3 H 7 Ketone O || 4. Carboxylic Acids (Alkanoic Acids) − C − OH Physical Properties Of Ethanoic Acid 1. Colourless liquid having sour taste and a smell of vinegar. 2. The boiling point of ethanoic acid is 1180C. 3. When pure ethanoic acid is cooled, it freezes to form a colourless, ice like liquid called glacial ethanoic acid. 4. Ethanoic acid is miscible with water in all proportions. Chemical Properties Of Ethanoic Acid 1. Action On Litmus Ethanoic acid is acidic in nature, being acidic in nature, ethanoic acid turns blue litmus solution red. 2. Reaction With Sodium Carbonate Ethanoic acid reacts with sodium carbonate to form sodium ethanoate and carbon dioxide gas. 2 CH 3 COOH + Na 2 CO 3 → 2 CH 3 COONa + CO 2 + H2O All carboxylic acids react in a similar way. 3. Reaction With Sodium Hydrogen Carbonate Ethanoic acid reacts with sodium hydrogen carbonate to evolve brisk effervescence of carbon dioxide gas. CH 3 COOH + NaHCO 3 H2O Homologous Series Of Carboxylic Acids Carboxylic acids form homologous series as follows: Nomenclature Of Carboxylic Acids IUPAC System The carboxylic acids are named as alkanoic acids. The IUPAC name is obtained by replacing the last e of the parent alkane by oic and adding the word acid to the name obtained. General Formula R –COOH → CH 3 COONa + CO 2 + All aldehydes react is a similar way. 4. Reaction With Alkalis (Sodium Hydroxide) Ethanoic acid reacts with alkalis to form salts and water. Ethanoic acid reacts with sodium hydroxide to form sodium ethanoate and water. CH 3 COOH + NaOH → CH 3 COONa + H 2 O All Carboxylic acids reacts in a similar way. 5. Or –COOH The carbon compounds containing carboxyl group (--COOH) are called carboxylic acids. The carboxylic acids are made up of three elements i.e., carbon, hydrogen and oxygen. Formula HCOOH CH 3 COOH C 2 H 5 COOH C 3 H 7 COOH C 4 H 7 COOH Ethanoic Acid (Acetic Acid) General Formula CH 3 COOH A dilute solution of ethanoic acid in water is called vinegar. Homologous Series Of Ketones Ketones form the following homologues series. Nomenclature Of Ketones IUPAC Naming The last e of the parent alkane is replaced by one. IUPC Name Methanoic Acid Ethanoic Acid Propanoic Acid Butanoic Acid Pentanoic Acid H2O Reaction With Alcohols (Esterification) Ethanoic acid reacts with alcohols in the presence of a little concentrated sulphuric acid to form esters. CH 3 COOH + C 2 H 5 OH Conc.H SO 4 2 → CH 3 COOC 2 H 5 + All carboxylic acids react in a similar way. 6. Saponification That reaction in which carboxyl group is removed (i.e. a molecule of CO 2 ) is called decarboxylation reaction. When sodium ethanoate is heated with soda lime, the methane gas is formed. CH 3 COOC 2 H 5 CH 3 COONa + NaOH Heat → C 2 H 5 OH + Chemical Properties Of Carbon Compounds All carboxylic acids react in a similar way. Uses Of Ethanoic Acid 1. Dilute ethanoic acid (vinegar) is used as a food preservative in the preparation of pickles and sauces. It is also used as an appetizer for dressing food dishes. 2. Ethanoic acid is used for making cellulose acetate, which is an important artificial fibre. 3. It is used in the manufacture of acetone and esters in perfumes. 4. It is used in the preparation of dyes, plastics and pharmaceuticals. 5. It is used to coagulate rubber from latex. 6. It is used for making white lead used as a white paint. 7. It is used as a reagent in chemistry laboratory. 5. Halogens –X The halogen group consists of elements of group 17 of the periodic table. Nomenclature Of Halogens IUPAC System The halogens are named by placing prefixes with the name of the alkane to which it is attached. The prefix will depend upon the particular halogen to which it is attached. 1. Combustion Carbon in all its allotropic forms burns in oxygen to give carbon dioxide, heat and light. Most carbon compounds also release a large amount of heat on burning. C + CH 4 + Light O2 O2 → CO 2 → CO 2 + Heat and Light + H2O + Heat and Saturated hydrocarbons will generally give a clean flame while unsaturated carbon compounds will give yellow flame with lots of black smoke also called a sooty flame. However a limited supply of air results in incomplete combustion of even saturated hydrocarbons giving a sooty flame. 2. Oxidation In the oxidation process only limited supply of oxygen is given to carbon compounds so as to add oxygen to them. Some substances are capable of adding oxygen to others, they are called oxidizing agents. For example alkaline potassium permanganate and acidified potassium dichromate are strong oxidizing agents. By the oxidation of alcohols they can be converted into carboxylic acids. Alkaline KMnO 4 + Heat CH 3 COOH + H 2 O CH 3 CH 2 OH + 2[O] → Or acidifiedK 2 Cr2 O7 + Heat Ethanol Chloro-methane Chloro-propane Common Name Methyl chloride Ethyl chloride Propyl chloride Butyl chloride Pentyl chloride Bromo- propane IUPC Name Chloro methane Chloro ethane Chloro propane Chloro butane Chloro pentane Formula CH 3 Cl C 2 H 5 Cl C 3 H 7 Cl C 4 H 9 Cl C 5 H 11 Cl Ethanoic Acid 3. Addition Reactions Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons. This reaction is generally used in the hydrogenation of vegetable oils using a nickel catalyst. Catalyst A catalyst is a substance that causes a reaction to occur or proceed at a different rate without the catalyst itself being affected. Hydrogenation Of Alkynes 6. Esters –COO– Esters are chemical compounds consisting of a carbonyl group adjacent to an ether linkage. Ethyl ethanoate Nomenclature Of Esters An ester name has two parts - the part that comes from the acid and the part that comes from alcohol. First the name of the alkyl derived from alcohol is written. This is followed by the name of the parent chain form the carboxylic acid part of the ester with an –e remove and replaced with the ending –oate. Common Name Methyl acetate Ethyl acetate Propyl acetate Butyl acetate Pentyl acetate IUPC Name Methyl ethnoate Ethyl ethanoate Propyl ethanoate Butyl ethanoate Pentyl ethanoate Formula CH 3 COOCH 3 CH 3 COOC 2 H 5 CH 3 COOC 3 H 7 CH 3 COOC 4 H 9 CH 3 COOC 5 H 11 Halogenation of Alkynes 4. Substitution Reactions Those reactions in which one type of atom or a group of atoms takes the place of another are called substitution reactions. Saturated hydrocarbons are unreactive and are inert in the presence of most reagents. However in the presence of sunlight chlorine can be added to hydrocarbons in a very fast reaction. Chlorine can replace hydrogen atoms one by one. Therefore it is called a substitution reaction. Sunlight + Cl 2 + HCl CH 4 → CH 3 Cl Chloro Methane CH 3 Cl + Cl 2 → CH 2 Cl 2 + Cl 2 CHCl 3 + HCl → Trichloro Methane (Chloroform) CHCl 3 Cl 2 CCl 4 + HCl → TetrachloroMethane( Carbon tetrachloride) + CH 2 Cl 2 + HCl Dichloro Methane Soaps And Synthetic Detergents Detergent Any substance which has cleansing action in water is called detergent. There are two types of detergents: 1. Soapy detergents (Soaps) 2. Non-Soapy detergents (Synthetic Detergents) (iv) During cleansing, the hydrocarbon part attaches itself to dirt. (v) On agitation in washing machine or rubbing with hands, the oil and grease surrounded by soap are removed from dirty surface and break in to fragments. (vi) The ionic part of the soap molecule, remains attached to water. (vii) When clothes are rinsed in water the dirt particles attached to soap molecule get washed away in water and the cloth gets cleaned. Limitations Of Soaps Soaps A soap is a sodium salt of a long chain carboxylic acid which has cleaning properties in water. Examples Sodium stearate, sodium oleate, sodium palmitate. 1. Soap Does Not Work Effectively In Hard Water Hard water contains calcium ions and magnesium ions. These ions present in hard water reac5 with the carboxylate ions of the soap forming on insoluble precipitate called scum. Types Of Soaps 1. Hard Soaps Sodium salts of fatty acids are known as hard soap. They are prepared from cheap oils and fats and sodium hydroxide. They have free alkali and are used for washing clothes. The scum sticks to the clothes, utensils and skin. Thus soap looses its properties of cleansing in hard water. 2. Soft Soaps They are prepared from good oils and potassium hydroxide. They are free from alkali, form more lather and are used in toilet soaps, shaving creams, shampoos. Structure Of Soap Molecule A soap molecule consists of two parts (i) A long hydrocarbon chain (hydrophobic) (ii) A short ionic part (hydrophilic) C17 H35 COONa + Ca2 + → ( C17 H35 COO 2. Soap Does Not Work In Acidic Solutions Acidic water contains H+ ions. When soap is dissolved in acidic water, its carboxylate ions ( RCOO − ) react with H + ions forming back the free fatty acids. C 17 H 35 COO − + H + → C 17 H 35 COOH The soap thus looses its property of cleansing. Synthetic Detergent (Soap Less Soap) Chemically detergents are sodium salts of long chain benzene sulphonic acid or a long chain alkyl hydrogen sulphate which has cleansing property in water. Example Sodium n-Dodecyl Benzene Sulphonate CH 3 – (CH 2 ) 11 – C 6 H 4 – SO 3 Cleansing Action Of Soaps And Detergents The cleansing action of soaps and detergents follows the same principle. Soaps and detergents consists of a large hydrophobic (water repelling) hydrocarbon tail with a negative hydrophilic (water attracting) head. (ii) In solution polar water molecules surround the ions and not the organic part of the molecule. (iii) On dissolving soap or detergent in water the molecules gather together as clusters called micelles with tails sticking inwards and heads outwards. ) 2 Ca + 2Na + − Na + Structure Of A Detergent Molecule A synthetic detergent molecule consists of two parts (i) A long hydrocarbon chain (hydrophobic) (ii) A short ionic part (hydrophilic) (i) Disadvantages Of Synthetic Detergents Over Soaps (i) Some of the synthetic detergents are non-biodegradable hence cause pollution. (ii) Some detergents may cause harm to the skin due to prolonged use. Advantages Of Detergents Over Soaps (i) Synthetic detergents are effective in hard water. (ii) Synthetic detergents are effective in acidic water. (iii) Vegetable oils which are used for the preparation of soaps can be used for human consumptions. Differences Between Soaps And Detergents Soaps Detergents 1. Soap is a sodium or Detergents are sodium or potassium salt of higher potassium salts of long chain fatty acid. alkyl hydrogen sulphates. 2. Soaps are prepared from Synthetic detergents are natural fats and oils. prepared from hydrocarbon obtained from petroleum. 3. They are biodegradable. They are non biodegradable. 4. Soaps are not suitable for Detergents can be easily washing in hard water. used even in hard water. 5. They cannot be used in They can be used easily in acidic medium as they are the acidic medium as they decomposed in the acidic are not decomposed in the medium. acidic medium.