CHEMISTRY CARBON AND ITS COMPOUNDS Carbon is a versatile element. In earth s crust, carbon is 0.02% and found in form of minerals. Atmosphere has 0.03% of Carbon dioxide. All living structures are carbon based. Covalent Bond in Carbon The atomic number of carbon is 6 and its electronic configuration is 2, 4. To attain a noble gas configuration it can 1. Gain 4 electrons. But it would be difficult for nucleus to hold 4 extra electrons. 2. Lose 4 electrons. But it would require a large amount of energy to remove 4 electrons. It is difficult thus for an atom of carbon to either gain or lose electrons. Carbon attains the noble gas configuration by sharing its valence electrons with other atoms. Atoms of other elements like hydrogen, oxygen, nitrogen, chlorine also show sharing of valence electrons. Formation of H2, O2 and N2 is shown as below : CATENATION: Property of carbon atom to form bond with other atoms of carbon is called catenation. Like carbon, silicon forms compounds with hydrogen up to seven or eight atoms of silicon. TETRAVALENCY: Having a valency of 4, carbon atom is capable of bonding with atoms of oxygen, hydrogen, nitrogen, sulphur, chlorine and other elements. The smaller size of carbon atom enables nucleus nucleus to hold the shared pair of electrons strongly, thus carbon compounds are very stable in general. BONDING IN CARBON AND ITS COMPOUNDS The atomic number of carbon is 6 and its ground state electronic configuration is 1s 2 2s 2 2p 2. Since it has four electrons in its outermost shell, its valency is four. To achieve noble gas configuration, carbon atom has to lose or gain four electrons to form C 4+ and C 4- ions. 1) It could gain four electrons forming C 4- anion, but it would be difficult for the nucleus with six protons to hold on to ten electrons i.e. four extra electrons. 2) It could lose four electrons to form C 4+ cations, but it would require a large amount of energy to remove four electrons leaving behind the carbon cations with six protons in its nucleus holding on to just two electrons. Carbon overcomes this problem by sharing its valence electrons with other atoms of carbon or with atoms of other elements. This characteristic of carbon atom by virtue of which it forms four covalent bonds is generally referred as tetra valency of carbon. A molecule of methane (CH 4 ) is formed when four electrons of carbon are shared with four hydrogen atoms.
Fullerenes: Physical nature of carbon and its compounds 1. Carbon has the ability to form covalent bonds with other atoms of carbon giving rise to large number 2. Carbon compounds have low melting and boiling points because of their covalent nature. CHEMICAL PROPERTIES 1) Carbon and its compounds burn in oxygen to give carbon dioxide along with heat and light. e.g., C + O 2 CO 2 + heat + light CH 4 + 2O 2 CO 2 + 2H 2 O + heat + light C 2 H 5 OH + 2O 2 2CO 2 + 3H 2 O + heat + light 2) Carbon compounds can be easily oxidized using suitable oxidizing agent (Alkaline potassium permanganate) to form carboxylic acids. 3) Unsaturated carbon compounds undergo addition reactions with hydrogen in the presence of palladium or nickel catalyst. e.g., Addition of hydrogen CH 2 = CH 2 CH 3 - CH 3 Ethene Ni-catalyst Ethane 4) Carbon compounds undergo substitution reactions in the presence of either sunlight or any other reagents. E.g. methane undergoes substitution reaction to form different types of products. 5) Carbon compounds such as alcohols react with sodium to liberate hydrogen gas. e.g.: 2CH 3 CH 2 OH + 2Na 2CH 3 CH 2 ONa + H 2 HOMOLOGOUS SERIES: A homologous series is a group or a class of organic compounds having similar structure and similar chemical properties in which the successive compounds differ by a CH2 group. Characteristics of homologous series 1) Each member of the series differs from the preceding or succeeding member by a common difference of CH2 and by a molecular mass of 14 amu (amu = atomic mass unit). 2) All members of homologous series contain same elements and the same functional groups. 3) All members of homologous series have same general molecular formula. e.g Alkane = C n H 2n + 2 Alkene = C n H 2n Alkyne = C n H 2n 2 4) The members in homologous series show a regular gradation in their physical properties with respect to increase in molecular mass. 5) The chemical properties of the members of the homologous series are similar. 6) All members of homologous series can be prepared by using same general method. IMPORTANCE OF HOMOLOGOUS SERIES 1) It helps to predict the properties of the members of the series that are yet to be prepared. 2) Knowledge of homologous series gives a systematic study of the members. 3) The nature of any member of the family can be ascertained if the properties of the first member are known.
NOMENCLATURE OF CARBON COMPOUNDS: 1. Identify the number of carbon atoms in the compound. 2. Functional group is indicated either by prefix or suffix. 3. If a suffix is added, then final e is removed from the name e.g. Methanol (methane-e = methan + ol). Functional Group Suffix Prefix Alkene ene Alkyne yne Alcohol ol Aldehyde al Ketone one Carboxylic acid oic acid chlorine chloro ESTERIFICATION: Carboxylic acids react with alcohols in presence of few drops of concentrated sulphuric acid as catalyst and form sweet smelling compounds called ester. Hydrolysis: On heating with an acid or a base the ester forms back the original alcohol and carboxylic acid. *Alkaline hydrolysis of ester is also called saponification.
SOAPS AND DETERGENTS Soap is sodium and potassium salt of carboxylic acids with long chain. Soaps are effective with soft water only and ineffective with hard water. Detergents are ammonium or sulphonate salts of carboxylic acids with long chain. They are effective with both soft as well as hard water. An ionic part (hydrophilic) and a long hydrocarbon chain (hydrophobic) part constitute the soap molecule.
Points to remember:- 1) Carbon forms a large variety of compounds because of its tetravalency and the property of catenation. 2) Hydrocarbons are the compounds of carbon and hydrogen. 3) Hydrocarbons are of two types saturated hydrocarbons (alkanes) and unsaturated hydrocarbons (alkenes and alkynes) 4) Carbon forms covalent bonds with itself and other elements such as hydrogen, oxygen, sulphur, nitrogen and chlorine. 5) The functional groups such as alcohols, aldehydes, ketones and carboxylic acids bestow characteristic properties to the carbon compounds that contain them. 6) A group / series of hydrocarbons having similar structure and similar properties (i.e. same functional group) are called a homologous series. 7) Carbon chains may be in the form of straight chains, branched chains or rings. 8) Carbon compounds with identical molecular formula but different structures are called structural isomers. 9) Saturated hydrocarbons on combustion give carbon dioxide and water with lots of heat.
10) Unsaturated hydrocarbons undergo addition reactions while saturated hydrocarbons undergo substitution reactions. 11) Ethanol and Ethanoic acid (glacial acetic acid) are carbon compounds of importance in our daily lives. 12) The molecules of soap are sodium or potassium salts of long chain carboxylic acids. 13) Detergents are ammonium or sulphonate salts of long chain carboxylic acids. 14) The action of soaps and detergents is based on the presence of both hydrophobic and hydrophilic groups in the molecule and this helps to emulsify the oily dirt and hence its removal. QUESTION BANK Q.1 Why is carbon tetravalent? Ans: Carbon atom has 4 electrons in the outermost shell. It needs 4 more electrons to complete its octet. Therefore, carbon is tetravalent. Q.2 The formula of a hydrocarbon is Cn H 2 n. Name the family to which it belongs and also predict its nature. Ans: The hydrocarbon belongs to alkenes It is unsaturated in nature. Q.3 What is the valency of carbon in CH 3 -CH 3, CH 2 =CH 2 and HC=CH? Ans: The valency of carbon in all its compounds whether saturated or unsaturated is 4. Q.4 Out of butter and ground nut oil, which is unsaturated in Nature? Ans: Groundnut oil is unsaturated in nature. Q.5 Why is high temperature not favorable for alcoholic fermentation? Ans: The high temperature destroys the enzymes which are needed to carry fermentation. Q.6 Name a cyclic unsaturated hydrocarbon, containing three double bonds? Ans: Benzene Q.7 What is the difference in the molecular mass of any two adjacent homologues? Ans: 14 mass units. Q.8 Which has triple bond; C 2 H 4,C 3 H 6 and C 3 H 4? Ans:C 3 H 4 has triple bond in the formula. Q.9 Which substance is added to denature ethyl alcohol? Ans: A small amount of methyl alcohol, pyridine or copper sulphate is added to denature ethyl alcohol. Q.10 Which ions are responsible for making water hard? Ans: Ca 2 + and Mg 2 + ions are responsible for making water hard. Q.11 Name the catalyst commonly used in hydrogenation of oil to form fats? Ans:Nickel. Q.12 Write the name and molecular formula of alcohol derived from butane? Ans: C 4 H 9 OH Butanol Q.13 Which gas is evolved when sodium carbonate or bicarbonate is added to ethanoic acid? Ans : CO 2 (carbon dioxide). Q.14 What is SCUM? Ans: Scum is precipitate of Calcium and Magnesium salt of organic fatty acids. Q.15 What are hydrophobic and hydrophilic parts in soaps? Ans: The alkyl group(r) consisting of long chain of carbon atom is hydrophobic part while COONa group is hydrophilic in nature. Q.16 What name is given to the reaction which take place when Ethanoic acid reacts with ethanol in the presence of conc. Sulphuric acid? Name the products obtained in this reaction. Ans-When ethanoic acid reacts with ethanol in presence of conc. H2SO4.the reaction is called esterification.in this reaction products formed are ethyl ethanoate and water. CH 3 COOH+CH 3 CH 2 OH CH 3 COOCH 2 CH 3 +H 2 O
Conc. H 2SO 4 Q.17 What is bromination? Write the structural formula of product obtained on bromination of propene. Ans The addition of bromine to unsaturated hydrocarbon is called bromination. H-CH 2 -CH=CH 2 +Br 2 CH 3 -CHBr-CH 2 Br Q.18 Define covalency? Ans-The number of electrons contributed by an atom in the formation of a covalent bond is called the covalency. The covalency of an element in a covalent compound is equal to the number of covalent bond formed by an atom of the element with other atom. Q19. Write the structural formula of the isomers of n-butane? Ans- i -CH 3 -CH 2 -CH 2 -CH 3 n-butane. ii-ch 3 -CH-CH 3 iso-butane I CH 3 Q20.Name the organic acid present in vinegar. Write its Chemical formula also. Ans-Ethanoic acid. Its chemical formula is CH 3 COOH. Q 21. The structural formula of an ester is HCOOCH2CH2CH3 write the formula of acid and the alcohol from which it is made? Ans-To write the formula of the acid and the alcohol add COO bond of the ester so that OH goes with CO part; Acid HCOOH and the alcohol CH 3 CH 2 CH 2 OH. Q22. What happens when ethanol reacts with (i) sodium (ii) potassium permanganate solution. Ans-(i) with sodium metal, sodium ethoxide formed. 2CH 3 CH 2 OH+2Na 2CH 3 CH 2 ONa + H 2 (ii) With alkaline potassium permanganate, ethanol is oxidized to ethanoic acid. CH 3 CH 2 OH+2[O] KMnO 4 (ii)dil.h 2 SO 4 CH 3 COOH+H 2 O Q23. What is hydrogenation? Write its industrial application. Ans- The addition of hydrogen to an unsaturated hydro- carbon is called hydrogenation. This process takes place in the presence of nickel or palladium metal as catalyst. i) It is used to prepare vegetable ghee from vegetable oil. ii) Vegetable oil such as ground nut, cottonseed oil are unsaturated and contain double bonds (C=C) on hydrogenation in the presence of catalyst, vegetable oil produces vanaspati ghee. Q24.Give a test that can be used to differentiate between butter and cooking oil? Ans-If a carbon compound decolorises bromine water, it will be an unsaturated compound. Thus we can distinguish between a cooking oil and butter. i) Cooking oil decolorises bromine water, this shows that it is an unsaturated compound. ii) Butter does not decolorise bromine water.this shows that it is a saturated compound.
Q25.Give the names of the functional group;- (i) CHO (ii) -C=O ( iii) OH (iv) COOH Ans- (i) Aldehyde group (ii) Ketone group (iii) alcoholic (iv) carboxylic Q26. Explain the following terms: a) Etherification b) Saponification c) Dehydration ANS [a] the reaction between a carboxylic acid and an alcohol in presence of a few drops of conc. H2SO4 to form an ester is called etherification. ANS [b] Saponification Alkaline hydrolysis of an ester to give the salt of the corresponding acid and the alcohol is called saponification. It is reverse of Esterification. For example, ANS [c] Dehydration means removal of a molecule of water. When ethanol is heated with conc. H2SO4 at 443K, it undergoes dehydration to form ethene. Q 27. An organic compound A having molecular formula C2H4O2 reacts with Sodium metal Na evolves a gas B which readily catches fire. A also reacts with Ethanol in the presence of concentrated Sulphuric acid to form a sweet smelling substance C in making perfumes. a) Identify the compounds A, B and C. b) Write balanced chemical equation to represent the conversion of i. Compound A to compound B. ii. Compound A to compound C. ANS [2-i] Since the Organic compound A with molecular formula C2H4O2 reacts with sodium metal to form a gas B which catches fire, therefore, gas B must be H2 and compound A must be ethanoic acid. 2CH 3 COOH + 2Na 2CH 3 COONa + H 2 Ethanoic acid (Sodium ethanoate) hydrogen, [Catches fire] ANS [2-ii] we know that esters are sweet smelling substances which are used in perfumes. These are formed when a carboxylic acid reacts with an alcohol in presence of conc. H2SO4. Since new compound A (i.e., Ethanoic acid) reacts with ethanol (an alcohol) in presence of conc. H2SO4 to form a sweet smelling substance which is used in perfumes, therefore; C must be an Ester, i.e., ethyl ethanoate. CH 3 COOH + CH 3 CH 2 OH Conc. H 2SO 4 CH 3 COOCH 2 CH 3 + H 2 O Ethanoic acid A Ethanol Ethyl ethanoate C (Sweet smelling substance) Q28. Give the name of the following : a) An Aldehyde derived from Ethane. b) Ketone derived from Butane. c) The compound obtained by the Oxidation of Ethanol by Chromic anhydride. ANS i. Ethanal [CH3CHO] ii. Butanone [CH3COCH2CH3] iii. Ethanal [CH3CHO]
Q29. Write chemical equations of the reactions of Ethanoic acid with : ` a) Sodium b) Sodium Carbonate c) Ethanol in the presence of conc. H2SO4. ANS [4] (1) 2CH 3 COOH + 2Na 2CH 3 COONa + H 2 (sod. Ethanoate) (2) 2CH 3 COOH + Na 2 CO 3 2CH 3 COONa + CO 2 + H 2 O (3) CH 3 COOH + C 2 H 5 OH CH 3 COOC 2 H 5 (ethyl ethanoate) + H 2 O H 2SO 4 (conc.) Q30. Give a test to distinguish between: a) Ethane and Ethene b) Ethanol with Ethanoic acid. c) Soaps and detergents i. Ethene decolorizes the Reddish brown colour of Bromine water while ethane does not. ii. Ethanoic acid gives a brisk effervescence with sodium hydrogen carbonate while ethanol does not. iii. Soaps form curdy white precipitate or scum with hard water while detergents do not form any recipitate. Q31. Two carbon compounds A and B have the molecular formula C3H8 and C3H6 respectively. Which one of the two each most likely to show addition reaction? Justify your answer. Explain with the help of a chemical equation, how an addition is useful in vegetable Ghee industry. [Ans ] C3H8 corresponds to the general formula CnH2n+2 (n =3), therefore its an alkane which is a saturated compound. The molecular formula, C3H6 corresponds to the general formula CnH2n (n=3) therefore it is an alkene, which is an unsaturated compound. Since alkenes contain a double bond, therefore C3H6 is more reactive than C3H8. H2 is added in presence of a catalyst to form saturated hydrocarbons for example, This addition reaction is useful in industry for converting vegetable ghee. Vegetable oils contain a number of unsaturated carbon chains having double bonds between carbon atoms. When H2 gas is bubbled through vegetable oils in presence of Nickel as catalyst at 473K, some of these double bonds add H2 to form saturated carbon chains. As a result of this partial hydrogenation, vegetable ghee is formed. Q32. What substance should be oxidized to prepare acetic acid (CH3COOH)? How can ethanol and Ethanoic acid are differentiated? [Ans ] Ethanol on oxidation with alkaline KMnO4 gives acetic acid. Ethanol and Ethanoic acid be differentiated by: Action with sodium hydrogen carbonate - On adding a small amount of sodium hydrogen carbonate to Ethanoic acid, carbon dioxide gas is evolved with brisk effervescence. However, no such reaction is noticed in case of ethanol. CH 3 COOH + NaHCO 3 CH 3 COONa + CO 2 + H 2 O Q33. Write down the difference between soap and detergents. SOAPS DETERGENTS (i) Soaps are sodium or potassium salts of higher (i) Detergents are mostly sulphonates of long chain fatty acids i.e. carboxylic acids obtained from oil hydrocarbons. and fats (ii) Soaps cannot work effectively in hard water (ii) Detergents can work equally well in hard and soft water (iii) Soaps cannot be used in neutral or acidic sol. (iii) Detergents can be used in acidic, alkaline or neutral iv) Soaps are prepared from vegetable Oils animals fats which are scarce. sol. (iv) Detergents are manufactured from hydrocarbons obtained from coal or petroleum
Q34. An organic compound A is widely used as a preservative in pickles and has a molecular formula C 2 H 4 O 2. This compound reacts with ethanol to form a sweet smelling compound B. i) Identify the compound A. ii) Write the chemical equation for its reaction with Ethanol to form compound B. iii) How can we get compound A back from B? iv) Name the process and write corresponding chemical equation. v) Which gas is produced when compound A reacts with washing soda? Write the chemical equation Ans: (i) The compound A with molecular formula C 2 H 4 O 2 is ethanoic acid also called acetic acid. Its structural formula is CH 3 COOH. A dilute sol. of acetic acid called vinegar is used as preservative of pickles. (ii) Compound A reacts with ethanol to form compound B which is an ester and has pleasant smell. The reaction is called esterification reaction. CH 3 COOH + C 2 H 5 OH CH 3 COO C 2 H 5 + H 2 O Ethanoic acid Ethyl ethanoate (iii) The compound A can be obtained from ethyl ethanoate by reacting with water in presence of dilute hydrochloric acid acting as catalyst. dil.hcl CH 3 COO C 2 H 5 + H 2 O Ethyl ethanoate CH 3 COOH + C 2 H 5 OH Ethanoic acid (iv) This process is known is ester hydrolysis (v) Carbon dioxide gas is evolved with effervescence when the compound A reacts with washing soda which is chemically Na 2 CO 3. 2CH 3 COOH + Na 2 CO 3 2 CH 3 COONa + H 2 O + CO 2 The gas can be identified by passing through lime water which turns milky.