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LECTURER IN CHEMISTRY BANGURNAGAR COMPOSITE P.U.COLLEGE DANDELI – 581325 [ NORTH CANARA ] Empirical formula & Molecular formula Hydrocarbon – I 1. Empirical formula : Simplest formula which shows ratio of atoms of different elements present in the molecule 2. Molecular formula : Shows actual number of atoms of different elements present in the molecule 3. Simple problems based on empirical formula & molecular formula Hydrocarbon – I 1. Saturated hydrocarbon - contains C-C single bond 2. Unsaturated hydrocarbon - contains C-C – double bond or C-C triple bond 3. Alkane - Cn H2n + 2 - Paraffins (little affinity) 4. Kolbe’s reaction : Alkanes are prepared by the electrolysis of aqueous solution of sodium or potassium salt of carboxylic acid Hydrogen is liberated at cathode Alkane is obtained at anode Methane can not be prepared by this method 5. Alkene Cn H2n - Olefin (Oil forming) Alkene are prepared by the dehydrohalogenation of alkylhalide Dehydrohalogenation reaction is carried out by using alcoholic KOH 6. Alkynes - Cn H2n - 2 Alkynes are prepared by Dehydrohalogenation reaction 7. Homolytic fission - free radicals are formed Hetrolytic fission – electrophiles, Nucleophiles or carbonium ion, carbanion are formed 8. 9. Chlorination of methane i) Chain initiation step - free radicals are formed ii) Chain propagation step – free radicals formed reacts with other molecules to form more free radicals iii) Chain terminations step - All free radicals combine to form molecules Markownikoff`s rule : Negative Part of reagent (unsymmetrical reagent) is added to carbon – carbon double bond of alkene (unsymmetrical molecule) which contains less hydrogen atom 10. Aromatic hydrocarbon – I Benzene is discovered by faraday Structure of Benzene is given by Kekule Isolation of Benzene toluene from light oil fraction of coal tar (00 C - 1700c ) Benzene, Toluene, xylene 90% Benzol fraction contains 70% Benzene and 25% Toluene and Thiophene 11. Benzene reacts with chlorine in the presence of bright sunlight to form Benzene hexachloride (Insectside) 12. Toluene reacts with mixture of con – HNO3 + con – H2SO4 to from TNT ( Tri nitro toluene ) an explosive Toluene is used in the manufacture of saccharine – sweeting agent Empirical formula & Molecular formula Hydrocarbon – I 1. Which of the following Alkane contains Primary, Secondary, Tertiary and Quaternary carbon atoms. (a) (CH3)3 - CH (b) (C2H5)3CH (c) (CH3)3 - C - CH2 – CH - (CH3)2 (d) (CH3)4 –C Answer : (c) (CH3)3 - C - CH2 – CH - (CH3)2 Note : 2 When an aqueous solution containing Sodium Acetate and Sodium Propionate is Electrolysed we get (a) Ethane (b) Propane (c) Butane (d) Ethane,Propane, Butane Answer : (d) Ethane,Propane, Butane Note : Kolbe`s electrolysis CH3- COONa CH3- CH2 COONa C2 H6 ( Ethane) C4H10 ( Butane) CH3- COONa + CH3- CH2 COONa C3H8 ( Propane) 3. A gas decoloures Alkaline KMnO4 ( Baeyer`s Regent) but does not give any precipitate with Ammonical AgNO3 the gas is a) Methane (b) Ethane Answer : (c) Ethene (c) Ethene (d) Ethyne Note : 1. Unsaturation in organic – compound is tested by using following reagent • Alkaline KMnO4 ( Colour of KMnO4 is decolourised ) • Bromine water ( Colour of Bromine water is decolourised) • Ozone ( formation of Ozonide) 2. Ammonical AgNO3 (Tollen`s reagent ) and Ammonical Cu2 Cl2 are used to test acidic hydrogen atom in alkynes 3. Acidic Hydrogen atom is present at the end of the triple bonded carbon atom. It is due to the higher electro negativity of the SP – Hybridized Carbon Atom 4. Methane is formed from the Hydrolysis of (a) Calcium Carbide (b) (c) Methanal Answer : (d) (b) Aluminum Carbide Ethanol Aluminum Carbide Note : 1. CaC2 + 2H2 O Ca (OH)2 + C2 H2 2. Al4 C3 + 12H2 O 4 Al (OH)3 + 3CH4 3. H- CHO + H2 O No reaction 4. C2 H5 OH + H2 O No reaction 5. A Metallic Carbide on treatment with water gives a colourless gas which burns readily in air and gives a red precipitate with Cu2 Cl2 + NH4 OH the gas is (a) Methane Answer : (b) Ethane (c) Ethene (d) Ethyne (d) Ethyne ( Acetylene) Note : MC2 + 2H2O C2H2 + Cu2 Cl2 M(OH)2 + C2H2 C2Cu2 + 2HCl Red ppt 6. Ethylene (Ethene) is used in making (a) Antifreeze (b) Solvent (d) Antifreeze, Solvent, Fumigant (c) Fumigant Answer : (d) Antifreeze, Solvent, Fumigant Note : • • • • • Antifreeze (Ethylene Glycol) A substance added to water in radiators of motorcar engines in order to lower the freezing point of water Solvent ( ethylene chloride ) Fumigant (ethylene oxide ) Distraction of bacteria, Insects by exposure to toxic – chemicals Mustard Gas ( war gas ) Artificial Ripening of fruits 7. Addition of HI on double bond of Propene yields Isopropyle Iodide and not n – Propyl Iodide as the major product, because addition proceeds through (a) A More stable Carbonium Ion (b) A More stable Carbanion (c) A More stable Free Radical (d) Nucleophile Answer : (a) A More stable Carbonium Ion Note : CH3–CH = CH2 + H+ 1) CH3 – +CH – CH3 Iso propyl carbonium ion(More stable) 2) CH3 –CH2 – +CH2 n-propyl carbonium ion(Less stable) 8. Markownikoff`s rule provide guidance of addition of HBr on ? (a) CH2 = CH2 (c) CH3 - CH = CH - CH3 (b) CH3 – CH = CH2 (d) (CH3 )2- C = C - (CH3 )2 Answer : (b) CH3 – CH = CH2 Note : Unsymmetrical molecule HBr adds to Unsymmetrical Alkene 9. Two jars A and B are filled with Hydrocarbons Br2 in CCl4 is added to these jars A does not decolourise the Br2 solution but B decolourises what are A and B (a) Alkane and Alkene (b) Alkene and Alkane (c) Alkene and Alkyne Answer : (d) Alkene & Benzene (a) Alkane and Alkene Note : 1. Alkane are saturated compounds do not decolourise Br2 / CCl4 2.Alkene are unsaturated compounds decolourise Br2/CCl4 (a) Acetone and Acetic Acid (b) Acetaldehyde and Acetic Acid (c) Acetaldehyde and Ethanol (d) Acetone and Acealdehyde Answer : (b) Acetaldehyde and Acetic Acid 11. A group of closely related compounds which can be expressed by a general formula and in which consecutive members differ by – CH2 group is called (a) An Electromotive series (b) A Homogeneous series (c) A Homologous series (d) A Heterogeneous series Answer : (c) A Homologous series (a) Benzene, Ethylhalide (b) Ethylhalide, Benzene (c) Acetaldehyde, Ethylhalide (d) Acetic Acid, Ethylhalide Answer : (a) Benzene, Ethylhalide 13. Benzene reacts with Chlorine to form benzene Hexachloride in the presence of (a) Nickel (b) Alcl3 (c) Bright Sunlight (d) Zn Answer : (c) Bright Sunlight Note : C6 H6 + 3Cl2 Bright sunlight C H Cl BHC Insecticide 6 6 6 14.Acetylene is used as an Anesthetic under the name of (a) Narcylene (b) Pyrene (c) Neopyrene (d) Puridine Answer : (a) Narcylene 15. Which of the following is the main component of heavy oil fraction of coal – tar (a) Cresol and Naphthol (b) Phenol (c) Toluene (d) β - Naphthylamine Answer : (a) Cresol and Naphthol Note : 1. Light oil fraction 00 - 1700 C 2. Middle oil fraction 1700 C - 2300 C Benzene, Toluene, Xylene Phenol, Naphthalene 3. Heavy oil fraction 2300 C - 2700 C Cresols, Naphthols 4. Green oil fraction 2700 C - 3400C Anthracene, Phenanthrene 16. Benzene is less reactive than Ethene and Ethyne towards addition reaction . This is due to (a) Cyclic Nature (b) Delocalisation of π – Electrons (c) SP2 Hybridization (d) Presence of 3 – Double Bonds Answer : (b) Delocalisation of π – Electrons Note : Stability of Benzene is due to Delocalisation of π - Electrons (resonance) 17. A compound with Empirical formula CH2 O has a vapor density of 30. It’s molecular formula is (a) C6H12O6 (b) C2H4O2 (c) C6H12O6 (d) C3H6O3 Answer : (b) C2 H4 O2 18. An organic compound containing C, H and N give the following on analysis. C = 40%, H=13.33% and N = 46.67% What would be it’s Empirical Formula.? (a) C2 H7 N (b) C2 H7 N2 (c) CH3 N (d) CH4 N Answer : (d) CH4 N Note : C H N 40 12 13.33 1 46.67 14 = 3.33 1 = 13.33 = 3.33 4 ∴ Empirical formula CH4 N 1 19. Empirical Formula of a compound is CH2O, if it’s molecular mass is 180, then the molecular formula will be (a) C H O (b) C5 H10 O5 (c) C3H6O3 (d) C4H8O4 6 12 6 Answer : (a) C6H12O6 20. An Organic compound on analysis give C = 54.5% O = 36.4% and H = 9.1% by mass It’s Empirical formula is (a) CH2 O (b) CH O2 (c) C2 H4 O (d) C3 H4 O Answer : (c) C2 H4 O Note : C H O 54.5 9.1 36.4 12 1 16 = 4.54 2 = 9.1 = 2.27 4 1 ∴ Empirical formula = C2 H4 O 21. Carbon in Benzene undergoes SP2 Hybridization and the bond angle is 120o. The shape of Benzene Molecule is (a) Linear (b) Planar Hexagonal (c) Pyramidal (d) Tetrahedral Answer : (b) Planar Hexagonal 22. Which of the following can be easily Sulphonated.? (a) Benzene (b) Toluene (c) Nitrobenzene (d) Chlorobenzene Answer : (b) Toluene Note : The electron releasing CH3 group in Toluene increases the electron density on benzene ring and hence facilitates the attack of Electrophile 23. According to Huckel, Monoclyclic compounds will show Aromaticity when. (a) It has 4 π Electrons (b) It has no π electron (c) It has 4π π + 2 Electrons (d) It has (4n + 2 ) π Electrons Answer : (d) It has (4n + 2 ) π Electrons Note : Huckel rule : “ The no. of π electrons in an aromatic ring is equal to (4n + 2 ) where ‘n’ is the number of benzene ring in the compound”. 24. Aromaticity of benzene is due to (a) Ring (b) Three double bonds (c) Delocalisation of π Electrons (d) Answer : Planar Molecule (c) Delocalisation of π Electrons 25. Which of the following is used for artificial Ripening of fruits (a) Ethene (b) Ethane (c) Methane (d) Ethyne. Answer : (a) Ethene 26.During the Chlorination of Methane to Methyl Chloride the propagation step is represented by Answer : Note : 1. Reaction ‘a’ Chain initiation step 2. Reaction ‘c’ Chain propagation step 3. Reaction ‘b’ & ‘d’ Chain termination step 27. Toluene can be separated from Benzene by (a) Washing with Con H2SO4 (b) Cooling in freezing mixture (c) Dissolving in Sodium Hydroxide (d) Steam distillation Answer : (b) Cooling in freezing mixture 28. The Hydrocarbon which is liquid at Room Temperature (a) Pentane (b) Butane (c) Propane Answer : (d) Ethane (a) Pentane Note : Lower member of Alkanes are gases. Pantane & Hexane are liquids. Higher members of Alkane are solids. 29.The molecular formula of a compound of a homologous series is C3H8O. The formula preceding it in the series is (a) C2 H6 O (b) C6 H10 O (c) CH4 O Answer : (d) C2 H5 O (a) C2 H6 O Note : Every member of a Homologous series differs by CH2 group. Hence the preceding member should be C3 H8 O - CH2 = C2 H6 O 30. The number of sigma and Pi bonds in a molecule of benzene is (a) 6 Sigma and 9 Pi (b) 9 Sigma and 3 Pi (c) 12 Sigma and 3 Pi (d) 6 Sigma and 6 Pi Answer : (c) 12 Sigma and 3 Pi 31.Methane when heated in the absence of Oxygen splits up to form Carbon & Hydrogen. The process is called (a) Pyrolysis (c) Cracking (b) Polymerisation (d) Decomposition Answer : (a) Pyrolysis Note : 1. Pyrolysis : Heating the substance at high temperature in the absence of Air or Oxygen 2. Polymerisation : Conversion of monomer to polymer 3. Cracking : Large molecule of heavy oil cracked into small one suitable for Petrol Engine 4. Decomposition : Breaking up of chemical compounds into smaller molecules 32. A salt producing Hydrocarbon among these compounds is (a) Methane (b) Ethane (c) Ethyne (d) Ethane Answer : (c) Ethyne Note : Ethyne forms Acetylides 33.Which of the products can not be obtained when Chlorine is passed into boiling Toluene (a) Benzyl Chlorine (b) Benzal Chloride (c) Benzotrichloride (d) O – Chlorotolune Answer : (d) O – Chlorotolune 34.In Benzene all the six C- C bonds have the same bond length because of (a) Resonance (b) Hybridisation (c) Isomerism (d) Chain Isomerism Answer : (a) Resonance 35. Molecule in which the distance between the two adjacent Carbon Atom is largest in (a) Ethane (b) Ethene (c) Ethyne (d) Benzene Answer : (a) Ethane Note : 1. Always single bond is larger than double or triple bond 2. In Benzene, due to delocalisation of π Electrons bond length is between single bond & double bond. For Fun Filled Holidays with Adventure visit www.dandeli.com