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Carbon and its compounds
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- 2. CARBON-INTRODUCTION • Carbon isan element. • It is a non-metal. • The atomic number of carbon is 6 and the atomic mass 12 u. • The amount of carbon present in the earth’s crust and atmosphere is very small. • All the living organisms, plants and animals, are made up of carbon based compounds called Carbon compounds. • A large number of things we use in our daily life are made up of carbon. • Carbon plays a very important role in our daily life. • It occurs in both free state and combined state in nature.
- 3. CARBON-UNIQUE FEATURES 1. Themost outstanding property of carbon is its ability to combine with itself, atom to atom, to form long chains. The property of self combination of carbon atoms to form long chains is useful to us because it gives rise to extremely large number of carbon compounds. The formation of strong bonds by carbon atoms among themselves and with other elements makes the carbon compounds exceptionally stable. This property of carbon is known as CATENATION. 2. The other property of carbon is that it’s valency is 4, it is a tetravalent element. So it needs to lose or gain 4 electrons to form an octet arrangement. In case of gaining electrons, it is not possible due to energy considerations. Since carbon atom is small in size, in case of losing electrons, it is not possible because the nucleus holds them strongly. So it always forms covalent bonds. It is due to the property of TETRAVALENCY.
- 4. ALLOTROPES OF CARBON •The various physical forms in which an element exists are called allotropes of the element. • The three allotropes of carbon are: 1. Diamond 2. Graphite 3. Buckminsterfullerene • Diamond and graphite are allotropes of carbon which are known for centuries. Buckminsterfullerene is the new allotropes of carbon which has been discovered recently.
- 5. DIAMOND • It isa colourless transparent substance having extra ordinary brilliance. • It is quite heavy, hard, good insulator and is the hardest natural substance known. • A diamond crystal is a vegiant molecule of carbon atoms, in which each carbon atom is linked to four other carbon atoms by strong covalent bonds. • The rigid structure of diamond makes it a very hard substance. • We know that a carbon atom has 4 Valence electrons. In a diamond crystal, each atom is linked to 4 other atoms by covalent bonds and hence all the 4 Valence electrons of carbon are used up in forming the bonds. Since there are no free electrons, a diamond crystal is a non-conductor of electricity. • Diamonds are used in cutting instruments like glass cutters, saw for cutting marble, and in drilling equipment. • They are used in making jewellery. • Sharp edged diamonds are used by eye surgeons to remove cataract from the eyes.
- 6. GRAPHITE • It isa greyish black opaque substance. • It is light in weight, soft and slippery to touch. • A graphite crysrltal consists of layers of carbon atoms or sheets of carbon atoms. Each carbon atom is linked to three other carbon atoms by strong covalent bonds to form strong hexagonal rings. • Due to sheet like structure, graphite is comparatively soft substance. • We knowledge that, in a graphite crystal each carbon atom is linked to three other carbon atoms and thus only three Valence electrons get used up in forming bonds. The fourth electron remains. Due to the presence of free electrons in a graphite crystal, it conducts electricity. • Powdered graphite is used as a lubricant for the fast moving parts of machinery. Since it is non-volatility, it can be used for lubricating those machine parts which operate at high temperatures. • Graphite is used for making carbon electrodes otlr graphite electrodes in dry cells and electric arcs. • It is used for making the cores of our pencils called pencil leads and black paints.
- 7. BUCKMINSTERFULLERENE • It isan allotropes of carbon containing clusters of 60-carbon atoms joined together to form spherical mirrors. • It is a football shaped spherical molecule in which 60-carbon atoms are arranged in interlocking hexagonal and pentagonal rings of carbon atoms. • There are 20 hexagons and 12 pentagon’s of carbon atoms in one molecule of buckminsterfullerene. • This allotropes was named after the American architect Buckminsterfullerene Fuller because its structure resembled the Frame work of dome shaped halls designed by Fuller for large International exhibitions. • Buckminsterfullerene is a dark solid at room temperature • It is neither very hard nor soft.
- 8. ORGANIC COMPOUNDS • Thecompounds of carbon are known as organic compounds. Apart from carbon, most of the organic compounds contain hydrogen and many organic compounds contain oxygen or other elements. So most of the organic compounds are hydrocarbons, or their derivatives. • Carbon compounds are covalent bonds having low melting and boiling points. • Most of the organic compounds are non-conductors of electricity. • Organic compounds occur in all living things like plants and animals. • Though oxides of carbon, carbonates, hydrogen carbonates and carbides are also carbon compounds but they are not considered to be organic compounds. Because their properties are very different from those of the common carbon compounds. • The study of carbon compounds such as hydrocarbons and their derivatives is called organic chemistry. • The study of carbon, carbonates, hydrogen carbonates and carbides is called inorganic chemistry.
- 9. HYDROCARBONS • A compoundmade up of hydrogen and carbon only are called hydrocarbons. • The important natural source of hydrocarbons is petroleum or crude oil. The natural gas above the petroleum also contains hydrocarbons. • There are mainly two types of hydrocarbons. 1. Saturated hydrocarbons 2. Unsaturated hydrocarbons
- 10. SATURATED HYDROCARBONS • Ahydrocarbon in which the carbon atoms are connected by only single bonds is called a saturated hydrocarbon. • They are also called as ALKANES. • These hydrocarbons are chemically not very reactive. They are quite unreactive. • The general formula of alkanes is CnH2n+2
- 11. UNSATURATED HYDROCARBONS • Ahydrocarbon in which the two carbon atoms are connected by a double bond or triple bond is called an unsaturated hydrocarbon. • Unsaturated hydrocarbons are more reactive as compared to saturated hydrocarbons. • They are of mainly two types: 1. Alkenes 2. Alkynes
- 12. ALKENES • An unsaturatedhydrocarbon in which the two carbon atoms are connected by a double bond is called an alkene. • The general formula for alkenes is CnH2n
- 13. ALKYNES • An unsaturatedhydrocarbon in which the two carbon atoms are connected by a triple bond is called an alkyne. • The general formula for alkynes is CnH2n-2
- 14. ALKYL GROUPS • Thegroup formed by the removal of one hydrogen atom from an alkane molecule is called an alkyl group. • For eg: methyl group and ethyl group. • Methyl group is formed by the removal of one hydrogen atom from methane. • Ethyl group is formed by the removal of one hydrogen atom from ethane. • The general formula of an alkyl group is CnH2n+1
- 15. GOLDEN RULE 1. Ifthe number of hydrogen atoms is “2 more” than double the number of carbon atoms, then it will be an alkane. 2. If the number of hydrogen atoms is “exactly equal” than double the number of carbon atoms, then it would be an alkene. 3. The number of hydrogen atoms is”2 less” than double the number of carbon atoms, then it would be an alkyne.
- 16. CYCLIC HYDROCARBONS • Hydrocarbonsin which the carbon atoms are arranged in the form of a ring are called cyclic hydrocarbons. • The saturated cyclic hydrocarbons are called cycloalkanes. • The general formula for cycloalkanes is CnH2n .Eg: cyclopentane • The unsaturated cyclic hydrocarbons are called aromatic compounds. Eg: benzene
- 17. NAMING OF HYDROCARBONS •The number of carbon atoms in a hydrocarbon is indicated by using the following stems: 1. One carbon atom- Meth 2. Two carbon atoms- Eth 3. Three carbon atoms- Prop 4. Four carbon atoms- But 5. Five carbon atoms- Pent 6. Six carbon atoms- Hex 7. Seven carbon atoms- Hept 8. Eight carbon atoms- Oct 9. Nine carbon atoms- Non 10. Ten carbon atoms- Dec • A saturated hydrocarbon containing a single bond is indicated by writing the word ‘ ane’ after the stem. • An unsaturated hydrocarbon containing a double bond is indicated by writing the word ‘ene’ after the stem. • An unsaturated hydrocarbon containing a triple bond is indicated by writing the word ‘yne’ after the stem.
- 18. ISOMERS • The organiccompounds having the same molecular formula but different structures are known as isomers. • The existence of two or more different organic compounds having the same molecular formula but different structures is called isomerism. • Isomerism is only possible with hydrocarbons having 4 or more carbon atoms. • Eg: normal butane has a straight chain whereas iso-butane has a branched chain.
- 19. HOMOLOGOUS SERIES • Justas all the elements having similar electronic structures show similar chemical properties and are placed in the same group of the periodic table, in the same way, all the organic compounds having similar structures show similar chemical properties and they are put together in the same group or series. • In a homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by 1 carbon atom and 2 hydrogen atoms. • The various organic compounds of a homologous series are called homologues.
- 20. CHARACTERISTICS OF AHOMOLOGOUS SERIES 1. All the members of a homologous seriescan be presented 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 14u. 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 masses.
- 21. FUNCTIONAL GROUPS • Anatom or a group of atoms which makes a carbon compound reactive and decides it’s properties or functions is called a functional group. • In an organic compound, any atom other than carbon and hydrogen, is called a heteroatom. • Some of the important functional groups present in organic compounds are: 1. Halogeno group 2. Alcohol group 3. Aldehyde group 4. Ketone group 5. Carboxylic acid group 6. Alkene group 7. Alkyne group
- 22. HALO GROUP • Thehalo group can be chloro, bromo, or iodo. • The elements chlorine, bromine, and iodine are collectively known as halogens. • They are represented by the general symbol –X. • When one hydrogen atom of an alkane is replaced by a halogen atom, we get a haloalkane. • They contain Cl, Br, or I as heteroatom.
- 23. ALCOHOL GROUP • Thealcohol group is made up of 1 oxygen atom and 1 hydrogen atom joined together. • This group is also known as alcoholic group or hydroxyl group. • The compounds containing alcohol group are known as alcohols. • The alcohols contain O as an heteroatom.
- 24. ALDEHYDE GROUP • Thealdehyde group consists of one carbon atom, one hydrogen atom and one oxygen atom joined together. • The aldehyde group is written as –CHO. • Thebcarbon arltom of the aldehyde group is attached to either a hydrogen atom or an alkyl group. • It is sometimes called aldehyde group. • The compounds containing this group are called as aldehydes. • It occurs at the end of a carbon chain.
- 25. KETONE GROUP • Thecarbon atom of ketone group is attached to two alkyl groups. • It is sometimes called ketonic group. • The compounds containing ketonic group are called ketones. • A ketone group always occurs in the middle of carbon chain. • The simplest ketone is propanone or also known as acetone, which is a very good solvent and is used as a nail polish remover.
- 26. CARBOXYLIC GROUP • Itis also just known as carboxylic group or carboxyl group. • The organic compounds containing carboxylic group are called carboxylic acids or organic acids. • They are also known as alkanoic acids. • The simplest carboxyl acid is formic acid, also known as methanoic acid. • The most common one is however, acetic acid which is also known as ethanoic acid.
- 27. FUELS • A fuelis a material that has energy stored in it. When a fuel is burnt, this energy is released mainly as heat. • Most of the common fuels are either free carbon or carbon compounds. • Most of the fuels which we use today are obtained from coal, petroleum, and natural gas. These are known as fossil fuels. • Fossils are the remains of the pre-historic animals or plants buried under the earth, millions of years ago. • The fuels such as coal and petroleum have some nitrogen and sulphur in them. So, when coal and petroleum fuels are burnt, they lead to the formation of oxides of nitrogen and sulphur which go into air, and are the major cause for acid rains.
- 28. COAL • It isa complex mixture of compounds of carbon, hydrogen and oxygen, and some free carbon. • Small amounts of nitrogen and sulphur are also present in coal. • Millions of years ago, due to earthquakes and volcanoes the forests were buried under the surface of the earth and got covered with sand, clay and water. • Due to high temperature and high pressure inside the earth, and in the absence of air, wood was converted into coal.
- 29. PETROLEUM • The crudeoil petroleum is a complex mixture of several solid, liquid and gaseous hydrocarbons mixed with water, salt and earth particles. • It was formed by the decomposition of the remains of extremely small plants and animals buried under the sea millions of years ago. • The chemical effects of pressure, heat and bacteria, converted the remains of microscopic plants and animals into petroleum oil and natural gas just as they converted forest trees into coal. • This conversion took place in the absence of oxygen. • The petroleum just got trapped between two layers of impervious rocks forming an oil trap. • Natural gas is above this petroleum oil.
- 30. FLAME • A flameis the region where the combustion of gaseous substances takes place. So 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 vaporise on heating, burn with a flame. • Flames are of two types: 1. Blue flame 2. Yellow flame • When fuels burn, the type of flame produced depends on the proportion of oxygen which is available for the burning of fuel. • Those solid and liquid fuels which do not vaporise on heating, burn without a flame.
- 31. BLUE FLAME • Whenthe oxygen supply is sufficient, then the fuels burn completely producing a blue flame. • The blue fame does not produce much light and is said to be non-luminous flame. • For eg: A gas stove has holes for air to mix properly with cooking gas. The cooking gas gets sufficient oxygen from the air and hence burns completely producing a blue flame.
- 32. YELLOW FLAME • Whenthe oxygen supply is insufficient then the fuels burn incompletely mainly producing a yellow flame. • The yellow colour of the flame is caused by the glow of hot, unburnt carbon particles produced due to the incomplete combustion of the fuel. • This yellow flame produces light and hence said to be as luminous flame. • For eg: when a candle is lighted, the wax melts, rises up the wick and gets converted into vapours. In a candle there is no provision for the proper mixing of oxygen for burning wax vapours. So the wax vapours burn in an insufficient supply of oxygen which leads to incomplete combustion of wax. • This in turn produces small unburnt carbon particles which rise in the flame, get heated and glow to give out yellowish light.
- 33. COMBUSTION • The processof burning of a carbon compound in air to give carbon dioxide, water, heat and light, is known as combustion. It is also called as burning. Most of the carbon compounds burn in air to produce a lot of heat. For eg: alkanes burn in air to produce a lot of heat due to which alkanes are excellent fuels. • The saturated hydrocarbons generally burn in air with a blue non-sooty flame. But however if the percentage of oxygen supply decreases the they burn with a sooty flame. • Note that it the bottom of the cooking utensils in our homes are getting blackened, it shows that the air holes of the gas stove are getting blocked and the fuel is not burning completely. • The unsaturated hydrocarbons burn in air with a yellow, sooty flame producing black smoke. But if they are burnt in the presence of pure oxygen they burn with a non-sooty flame. • Incomplete combustion produces a harmful gas called carbon monoxide and also release less amount of energy when compared to complete combustion.
- 34. SUBSTITUTION REACTIONS • Saturatedhydrocarbons being unreactive do not react with any substances. • Saturated hydrocarbons, however, undergo substitution reactions with chlorine in the presence of sunlight. • The reaction in which on or more hydrogen atoms of a hydrocarbon are replaced by some other atoms like chlorine, is called a substitution reaction. • If a substitution reaction takes place by chlorine, it is also called chlorination. • Substitution reactions are the characteristic properties of the saturated hydrocarbons.
- 35. ADDITION REACTIONS • Thereaction in which an unsaturated hydrocarbon combines with another substance to give a single product is called an addition reaction. • Addition reactions like the addition of hydrogen, chlorine, bromine are the characteristic property of the unsaturated hydrocarbons. • Addition reactions are given by all the alkenes and alkynes. • 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 catalyst. • The process of hydrogenation is used to prepare vegetable ghee from vegetable oils. • Vegetable oils containing unsaturated fatty acids are good for our health. The unsaturated fats like vegetable ghee, obtained by the hydrogenation of the oils are not good for our health. • The animal fats like butter are also saturated fats containing saturated fatty acids which are said to be harmful for health if consumed in large quantities.
- 36. ADDITION OF BROMINE •Other substances like chlorine and bromine also give addition reactions with unsaturated compounds. • The addition of bromine is important because it is used as a test for unsaturated compounds. Bromine is used in the form of bromine water. • Bromine water is red-brown colour due to the presence of bromine in it. When this is added to an unsaturated compound the red-brown colour of bromine water is discharged. • So, if an organic compound decolourises bromine water the compound is an unsaturated organic compound. But if no then the compound is a saturated one.
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- 38. PHYSICAL PROPERTIES • Ethanolis a colourless liquid having a pleasant smell and a burning taste. • It is a volatile liquid having a low boiling point of 78 C. • It is lighter than water. • Ethanol mixes with water in any proportion. The solubility of ethanol in water is due to the presence of hydroxyl group in it. • Ethanol containing 5% water in it is called rectified spirit. It is the commercial alcohol. • 100% pure ethanol is called absolute alcohol. • It is a covalent bond and does not contain any hydrogen ions, so it is a neutral compound and has no effect on litmus paper. • All the alcohols are however neutral compounds.
- 39. CHEMICAL PROPERTIES • Thechemical properties of ethanol which we would discuss here are: 1. Combustion 2. Oxidation 3. Reaction with sodium metal 4. Dehydration 5. Reaction with carboxylic acids • During combustion, the organic compound reacts rapidly with oxygen and breaks up completely to form carbon dioxide, water vapour, and a lot of heat and light are also produced. • But oxidation can be said as a controlled combustion. The organic compound combines with oxygen provided by an oxidising agent to form a new compound. The organic compound does not break down and much less heat and light energy is produced.
- 40. 1. COMBUSTION • Ethanolis highly inflammable liquid. It catches fire easily and starts burning. It burns readily in air to produce carbon dioxide, water vapour and releasing a lot of heat and light. • Since ethanol burns with a clear flame giving a lot of heat, it is used as an additive in petrol. • It is produced on large scale from sugar cane crop. Sugar is obtained from the sugar cane crop by the process of crystallisation. After the process, a thick and dark brown liquid called molasses is left behind. It still contains 30% of sugar. • Ethanol is produced from the fermentation of cane sugar present in molasses.
- 41. 2. OXIDATION • Anaqueous solution potassium permanganate containing sodium hydroxide is called alkaline potassium permanganate solution-KMnO4 + NaOH • The potassium dichromate solution containing sulphuric acid is called acidified potassium dichromate solution-K2Cr2O7 + H2SO4 • The above two are strong oxidising agents. • When ethanol is heated with alkaline potassium permanganate solution or acidified potassium dichromate solution, it gets oxidised to ethanoic acid.
- 42. 3. REACTION WITHSODIUM METAL • This reaction is used as a test for ethanol. • When a small piece of sodium metal is put into an organic liquid, and it results in evolving of hydrogen gas, then the organic liquid is an alcohol. 4. DEHYDRATION • Removal of water molecule from an alcohol is known as dehydration. • When ethanol is heated with excess of concentrated sulphuric acid at 170 C, it gets dehydrated to form ethene which is an unsaturated hydrocarbon. • In this reaction, concentrated sulphuric acid acts as a dehydrating agent.
- 43. 5. REACTION WITHETHANOIC 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 known as esterification. • Esterification takes place in the presence of catalyst like concentrated sulphuric acid.
- 44. USES OF ETHANOL •It is used in the manufacture of paints, varnishes, lacquers, medicines, perfumes, dyes, soaps and synthetic rubber. • It is used as a solvent. Many organic compounds insoluble in water, are soluble in ethanol. • Being a good solvent, it is used in medicines such as tincture iodine, cough syrups and many tonics. • It is used as a fuel I cars along with petrol. It is also used as a fuel in spirit lamps. • It is used in alcoholic drinks like whisky, wine, beer and others. whisky contains 35% of ethanol, wine about 10%-20% and beer about 6% of ethanol. • It is used as an antiseptic to sterilize wounds and syringes in hospitals and dispensaries.
- 45. HARMFUL EFFECTS OFDRINKING ALCOHOL • Alcohol slows down the activity of nervous system and brain due to which a person is impaired and his reaction becomes slow. • It lowers inhibitions-mental restrain and a drunken man becomes quarrelsome. • It leads to staggered movement, slurred speech, blurred vision, dizziness and vomiting and can even lead to death. • It makes a man alcoholic and financially bankrupt. • It damages internal organs and can cause a liver disease called ‘cirrhosis’. • Consumption of adulterated alcohol can make a person blind and even lead to death. • Moreover, consumption of methanol can lead to death.
- 46. DENATURED ALCOHOL •A lotof ethanol is used for industrial purpose for manufacturing various products. For this purpose, it is supplied to the industries at a cheaper rate by the government. •To prevent the misuse of industrial alcohol for drinking purposes, it is adulterated by adding small amounts of poisonous substances like methanol, pyridine or copper sulphate, thus making it unfit for human consumption.
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- 48. PHYSICAL PROPERTIES • Itis a colourless liquid having a sour taste and a smell of vinegar. • The boiling point of ethanoic acid is 118 C. • When pure ethanoic acid is cooled, it freezes to form a colourless, ice-like solid. Due to this, pure ethanoic acid is called glacial ethanoic acid. • Ethanoic acid is miscible with water in all proportions.
- 49. CHEMICAL PROPERTIES • Thechemical properties which we learn here are: 1. Action on litmus 2. Reaction with carbonates and hydrogencarbonates 3. Reaction with sodium hydroxide 4. Reaction with alcohols
- 50. 1. ACTION ONLITMUS • Ethanoic acid is acidic in nature. Being acidic, it turns blue litmus solution to red. • It shows orange colour in the universal indicator- ph is 4, showing that it is a weak acid. • Due to its acidic nature, it reacts with carbonates, hydrogencarbonates, bases to form salts.
- 51. 2. REACTION WITHCARBONATES AND HYDROGENCARBONATES a) REACTION WITH SODIUM CARBONATE b) REACTION WITH SODIUM HYDROGENCARBONATE • This reaction is used as a test for ethanoic acid. • The organic compound is taken in a test tube and a pinch of sodium hydrogencarbonate is added to it. Evolution of carbon dioxide gas with brisk effervescence shows that the given compound is a carboxylic acid. 3. REACTION WITH SODIUM HYDROXIDE
- 52. 4. REACTION WITHALCOHOLS • ethanoic acid reacts with alcohols in the presence of a little of concentrated sulphuric acid to form esters. • Esters are usually volatile liquids having sweet smell or pleasant smell. They are said to have a fruity smell. • They are used in making artificial perfumes. • One of the most important reaction of esters is that they can be hydrolysed back to alcohol and carboxylic acid. • When ester is heated with sodium hydroxide solution the ester gets hydrolysed. • The alkaline hydrolysis of esters using alkali like NaOH is known as saponification.
- 53. USES OF ETHANOICACID • Dilute ethanoic acid in the form of vinegar is used as a food preservative in the preparation of pickles and sauces. • It is used for making cellulose acetate which is an important artificial fibre. • It is used in the manufacture of acetone and esters used in perfumes. • It is used in the preparation of dyes, plastics, and pharmaceuticals. • It is used to coagulate rubber from latex.
- 54. SOAPS AND DETERGENTS •Any substance which has a cleansing action in water is called a detergent. • There are mainly two types of detergents: 1. Soapy 2. Non-soapy • Soapy detergents are generally called soaps. • Non-soapy detergents are generally called synthetic detergents.
- 55. SOAPS • A soapis a sodium salt of a long chain carboxylic acid which has cleansing properties in water. • A soap has a large non-ionic hydrocarbon group and a ionic group, • For eg: sodium stearate and sodium palmitate • Soap is made by heating animal fat or vegetable oil with concentrated sodium hydroxide solution- caustic soda solution. • The process of making soaps by the hydrolysis of fats and oils with alkalis is called saponification.
- 56. PREPARATION OF SOAPS •Materials required: vegetable oil, caustic soda and common salt. • Procedure: 1) Take about 20ml of vegetable oil in a beaker. 2) Add 30ml of 20% caustic soda solution to it. 3) Heat the mixture with constant stirring till a paste is formed. 4) Add 5-10g of common salt to it. 5) Stir the mixture and allow it to cool and then cut it into soap bars.
- 57. COMMON SALT INSOAP MAKING • Though most of the soap seperates out on its own but some of it still remains in the solution. • Common salt is added to precipitate out all the soap from the aqueous solution. • Actually, when common salt is added then the solubility of soap present in the solution decreases due to which all the soap seperates out from the solution in the form of a solid.
- 58. STRUCTURE OF ASOAP MOLECULE • A soap molecule is made up of two parts: a long hydrocarbon part and a short ionic part. • The soap molecule is said to have a tadpole like structure. • The long hydrocarbon part is hydrophobic-water repelling and the ionic part is hydrophilic-water attracting. • So the ionic part is soluble in water and not in oil or grease. • The hydrocarbon part is soluble in oil or grease and not in water, and thus this part attaches to the oil or grease stain. • Due to these two unique features a micelle is formed. • A spherical aggregate of soap molecules in a soap solution is called a micelle. • Note that a soap solution is a colloidal solution.
- 59. CLEANSING ACTION OFSOAP • When soap is dissolved in water, it forms a colloidal suspension in water in which the soap molecules cluster together to form spherical micelles. • Micelle formation takes place when soap is added to water because the hydrocarbon chains of soap molecules are hydrophobic and ionic ends are hydrophilic which dissolve in water. This formation does not take place in organic solvents like ethanol because the hydrophobic end also dissolves in it.
- 60. LIMITATIONS OF SOAP •When soap is used for washing clothes in hard water, a large amount of soap is wasted in reacting with the calcium and magnesium ions of hard water to form an insoluble precipitate called scum. Thus a larger amount of soap is needed for washing clothes. • The scum formed by the action of hard water sticks to the clothes being washed and interferes with the cleaning ability of the additional soap and makes cleaning difficult. • The formation of lather or foam is necessary for the cleaning process with soap but with hard water soap does not produce foam.
- 61. DETERGENTS • Detergents arealso called soap-less soaps because though they act like soap in having the cleansing properties, they do not contain the usual soaps like sodium stearate. • They are better than soaps because they do not form scum with hard water. • Unlike soap, a detergent can lather well even with hard water. • A detergent is a sodium salt of a long chain benzene sulphonic acid which has cleansing properties in water. • The cleansing properties and the structure is the same as a soap molecule. • For eg: sodium n-dodecyl benzene sulphonate and sodium n-dodecyl sulphate. • An important disadvantage of detergents over soaps is that some of the detergents are not biodegradable and cause pollution.
- 62. DIFFERENCES BETWEEN SOAPSAND DETERGENTS Soaps Detergents They are the sodium salts of the long chain carboxylic acids. They are the sodium salts of long chain benzene sulphonic acids. They are not suitable for washing purposes in hard water. They can be used for washing even in hard water. They are biodegradable. Some of them are non biodegradable. They have relatively wea cleansing action. They have strong cleansing action.