Organic Chemistry MCQs with Explanatory Answers

  

1.  The first organic compound prepared in the lab is:

(a) Methane

(b) Acetic acid

(c) Urea

(d) Glucose

Explanation; (c)

Urea or carbamide was the first organic compound prepared in the lab in 1828, by a German chemist Friedrich Wohler. Urea was accidentally prepared in the laboratory by controlled heating of inorganic salt, ammonium cyanate (obtained by double decomposition of ammonium chloride and potassium cyanate). This synthesis proved that there is no necessity of vital force for the preparation of organic compounds. Thus vital force theory was completely over thrown or discarded.

2.  Organic chemistry deals:

(a)All hydrocarbons
(b)All carbon compounds
(c)Hydrocarbons & their derivatives
(d)All of them 

Explanation; (c)

The study of covalent compounds of carbon containing H, and often O, N, S, P and halogens (Cl, Br and I) containing C – C bond is termed as Organic Chemistry. It is the study of hydrocarbons and their derivatives.

Organic compounds are compounds of carbon regardless of their origin. Carbon and hydrogen form the backbone of organic chemistry. The term halogen generally excludes fluorine as fluoro-carbon compounds and their reactions differ from other halogen chemistry.

Exceptions

However there are certain compounds of carbon which are not included in organic compounds. These are carbides (CaC₂), cyanides(NaCN), metal carbonates (Na₂CO₃), metal bicarbonates (NaHCO₃), cyanates (CNO¯), sulphocyanides (CNS¯) and oxides of carbon (CO and CO₂).

Carbon compounds such as carbonates, bicarbonates, oxides of carbon etc. are studied as inorganic compounds due to historical, conventional reasons and their properties are entirely different from organic compounds. In these compounds:

(i) Carbon does not have essential importance
(ii) Lack of C – C bond
(iii) Absence of functional grope

3. Which of the following element is not present in organic compounds?

(a) S
(b) N 
(c) O 
(d) Si

Explanation; (d)
Organic compounds along with carbon and H usually contains O, N, S, P and halogens (Cl, Br and I). Si is not present in organic compounds.

4. Urea was prepared by Wohler by boiling …………. with water:

(a) Ammonium chloride
(b)Ammonium sulphate
(c)Ammonium cyanate
(d)Ammonium cyanide

Explanation; (c)

Urea was prepared by boiling ammonium cyanate, NH₄CNO (obtained by double decomposition of ammonium chloride and potassium cyanate) with water. 

 

5. Which of the following is the important natural sources of organic compounds?

(a)Plants and Coals

(b)Petroleum
(c)Natural gas
(d)All of the above

Explanation; (d)

The natural sources of organic compounds includes plants, animals, coals, petroleum, natural gas. 

 

6.  Which of the following is a type of coal?

(a)Anthracite
(b) Bituminous coal
(c) Lignite (peat)
(d)All of them

Explanation; (d)

Coal is found in various forms (5 forms) which represent the different stages of conversion of vegetable matter:

7.  The hardest and the driest form of coal containing 92-98% C and burns without smoke is called:

(a) Anthracite
(b) Sub-bituminous coal
(c) Bituminous coal
(d) Lignite

Explanation; (a)

Anthracite is the hardest and the driest form of coal containing 92-98% C and burns without smoke.

8.  The thermal decomposition of coal (bituminous) in the absence of air at 500-1000°C gives coke, coke-oven gas (coal gas) and coal tar.  This process is called:

(a) Carbonization
(b) Fractional distillation
(c) Destructive distillation
(d) Both (a) and (c)

Explanation; (d)

Thermal decomposition of a highly carbonaceous material such as coal (bituminous) in the absence of air at 500-1000°C resulting in decomposition to solids (coke), liquids (coal tar) and gases (coal gas) is called Carbonization or Destructive Distillation.

The process is called carbonization as the solid end product is carbon.

Destructive distillation of bituminous coal is carried out in an iron retort by heating it to high temperature of 350–1000°C in the absence of air yielding coke, coal gas (coke-oven gas) and coal tar.

9. Which one is 100% pure carbon?
(a) Coke
(b) Coal gas
(c) Gas carbon
(d) Coal tar
Explanation; (a)
Coke is the purest form of carbon comprising almost 100% carbon.

10. Coal tar is considered as “a hidden treasure” because it consists of ……… aromatic organic compounds:

(a) 215

(b) 315

(c) 415

(d) 515

Explanation; (a)

Coal tar gives more than 215 aromatics upon fractional distillation. Hence it is considered as a hidden treasure of aromatic organic compounds. 

11.  The unrefined petroleum is called:

(a) Crude oil

(b) Rock oil

(c) Coal gas

(d) Both (a) and (b)

Explanation; (d)

The unrefined petroleum is called crude oil or rock oil.

1.     In Latin, petroleum means rock oil. It is also known as crude oil or black gold. It is found below the surface of the earth. Petroleum in the refined form is called mineral oil.

 

2.   It is believed to be formed by the anaerobic decay (slow bichemcial and chemcial decompsotion) of buried remains of living organisms or organic matter and is trapped as large reservoirs under the impermeable or sedimentary rocks.

3.    Petroleum is a naturally occurring thick viscous liquid of brown or greenish black colour with bad smell comprising of a mixture of hydrocarbons like alkanes, alkenes, cycloalkanes, aromatic hydrocarbons with small quantities of inorganic compounds of nitrogen, oxygen, and sulphur.

 

4. The predominate component of petroleum is alkanes. Petroleum contains alkanes upto C₄₀.

 

5.  Petroleum in the unrefined form is called Crude Oil or Rock Oil.

 

6.  The crude petroleum when subjected to fractional distillation, several groups of products called petroleum products are obtained.

 

7.  More than 500 compounds have been formed in petroleum distillate boiling below 200°C .That is why petroleum is the chief source of aliphatic compounds (hydrocarbons). It is also the main source of liquid fuels.

8.    About 60% of the world reserves of petroleum are in the Middle East while 15% are in Western Hemisphere. 

12. The process of a cracking takes place between temperatures:

(a) 1000–200°C
(b) 500–700°C 

(c) 500–600°C
(d) 500–800°C

Explanation; (d)

The optimum temperature for the process of cracking is 500–800°C. 

13.  Which one of the following is an addition polymer?

(a) Polytetrafluoro ethylene (PTFE)
(b) PVA
(c) PVC
(d)All of the above

Explanation; (d)

Polymers formed by the repeated addition of monomers by possessing the double or triple bonds.

If the addition is of the same species they are called homopolymers and if the addition is of different monomers they are called copolymers.

Example of Addition Polymers

14. PVC is a polymer of:

(a) Vinyl chloride
(b) Vinyl acetate
(c) Ethylene
(d) TFE

Explanation; (a)

Vinyl chloride is the monomer of Polyvinyl chloride (PVC). 

15.Nylon 6.6 is a:

(a) Polythene
(b) Polyamide
(c) Polyester
(d) None of the above
Explanation; (c)
Nylons are the synthetic fibres which contain long chain polyamide as fibre forming substance.

16. PVA is a polymer of: 

(a) Vinyl chloride
(b) Vinyl acetate
(c) Ethylene
(d) TFE
Explanation; (b)
Vinyl acetate is the monomer of polyvinyl acetate.

17. The condensation polymer of hexan-1,6-dioic acid (adipic acid) and 1,6–diaminohexane is called:

(a) Nylon
(b) Terylene
(c) Bakelite
(d) PVC

Explanation; (a)

Nylon is a condensation polymer of double acid dicarboxylic acid adipic acid (hexane-1,6-dioic acid, HOOC(CH₂)₄COOH) and double amine hexamethylene diamine (1,6-diaminohexane, H₂N(CH₂)₆NH₂). Thus nylon is a polyamide.

The same type of linkage is found in proteins.

The name nylon 6.6 is derived from the fact that both joining components contain six carbon atoms each.

It is different from natural silk in its structure but similar in appearance.

It is more elastic and finer in texture than silk.

It is used in hosiery where rayon has failed due to its inelasticity.

 

18.The polymer of Benz-1,4–dioic acid (terephthalic acid) and ethylene glycol is called:

(a) Nylon
(b) Terylene
(c) Bakelite
(d) PVC

Explanation; (b)

Terylene is a condensation polymer of ethylene glycol (ethane-1,2-diol) and aromatic double acid terephthalic acid (benz-1,4-dioic acid or benzene-1,4- dicarboxylic acid). [Since an acid and an alcohol react to form an ester, hence this fibre is also called polyester fibre]. Thus terylene is a polyester.

The trade name of terylene is Dacron. The same type of linkage is found in fats, oils and waxes.

It is produced by the condensation polymerization of ester formed by the esterification of terephthalic acid and ethylene glycol.

It is more resistant to water and has better sweat absorbing quality than nylon.

Its fabrics have more strength, resistant to heat, better texture and tailoring qualities. 

19.  The polymer of formaldehyde and phenol is called:

(a) Nylon

(b) Terylene

(c) Bakelite

(d) PVC

Explanation; (c)

In presence of dilute base, phenol reacts with formaldehyde to produce a mixture of ortho and para-methylol phenols which are polymerized into a condensation polymer, Bakelite (first synthetic plastic), a thermo-setting plastic, once moulded, it cannot be remoulded and remelted. 

20. Which one of the following is a type of isomerism?

(a) Chain or skeletal
(b) Stereo isomerism
(c) Metamerism
(d) All of the above

Explanation; (d)

21.  An acceptor of pair of electron is termed as

(a) Nucleophile

(b) Electrophile

(c) Carboanion 

(d)Anion 

Explanation; (b)

An Electrophile is an electron pair acceptor during a reaction. They are electron-deficient species with vacant orbital usually have positive charge. 

22. Butene with molecular formula C₄H₈ has ________ isomers.

(a) 2
(b) 3
(c) 4
(d) 6

Explanation; (c)

C₄H₈, an alkene can show geometrical isomerism, functional isomerism and structural isomerism. There are 3 possible structural isomers. They are But-1-ene, But-2-ene, 2-methylpropene.

2-Butene is the simplest alkene exhibiting cis/trans-isomerism (also known as (E/Z)-isomerism); that is, it exists as two geometric isomers cis-2-butene ((Z)-2-butene) and trans-2-butene ((E)-2-butene). Geometric isomerism (also known as cis-trans isomerism or E-Z isomerism) is a form of stereoisomerism. Thus there are total 4 possible isomers of C₄H₈.

23.          Decane has ________ isomers:

(a) 18
(b) 9
(c) 35
(d) 75

Explanation; (d)

Decane has 75 isomers.

No. of Possible Isomers of Alkane

24.          A nucleophile is a 

(a) Lewis base
(b) Arrhenius acid
(c) Lewis acid
(d) Arrhenius base

Explanation; (a)

A nucleophile is a chemical reagent which can donate an electron pair in a reaction to an electron deficient part to make a new covalent bond is called a nucleophile. They attack on the positive site of the substrate molecule or loves electron. Thus they act as an electron pair donor during a reaction. They are represented by N^‾ or  or Nu^‾. They are also called Lewis Base as they are electron-rich species and hence have an affinity for positive nucleus.

The name nucleophile means “nucleus-loving” which indicates that a nucleophile always attacks regions of low electron density (positive centers) in the substrate molecule due to sufficiency of electrons.

All nucleophiles are either negative ions or anions having negative charge (even partial) or neutral molecules with p-electrons or unshared or lone electron pair. All anions, unsaturated compounds (alkenes, alkynes, arenas) and compounds having lone pair of electrons are considered to be nucleophile.

25.  Which molecule has longest carbon chain?

(a) Iso-pentane
(b) Neopentane
(c) Neohexane 
(d) n-pentane 

Explanation; (d)

n-pentane has the longest carbon chain of 5.

Iso-pentane has the carbon chian of 4.

Neopentane has the carbon chain of 3.

Neohexane has the carbon chain of 4. 

26.  Which molecule all the least C-C distance?

(a) C₂H₆

(b) C₂H₄

(c) C₂H₂

(d) C₄H₈

Explanation; (c)

C–C bond distance is least in compound containing C≡C triple bond. C₂H₂ is ethyne containing C–C triple bond. 

27. What is the value of C–C bond length in ethyne?

(a) 154 pm
(b) 139 pm
(c) 134 pm
(d) 120 pm

Explanation; (d)

C–C bond length in ethyne is least (120 pm) as it contains carbon carbon triple bond. 

28. As number of C atom in homologous series increases, then which of the following will decrease?

(a) B.P/M.P

(b) Solubility

(c) Density

(d) Both a and c

Explanation; (b)

Solubility decreases with increasing molecular mass. 

29.Which of the following is the first member of ester homologous series?

(a) Ethyl ethanoate
(b) Methyl ethanoate
(c) Methyl methanoate
(d) Ethyl methanoate

Explanation; (c)

Methyl methanoate is the first member of ester series. 

30. Which of the following exist in gas and liquid State?

(a) Ethane

(b) Propane

(c) Butane

(d) Pentane

Explanation; (d)

Pentane exists in both gas and liquid state. n-pentane and neo-pentane are gases while iso-pentane is a gas.

31. Which of the following is used in nail polish remover and for storage of acetylene?

(a) Acetic acid

(b) Formaldehyde

(c) Propanone

(d) Ethanol

Explanation; (c)

Propanone or acetone is used in nail polish remover and for storage of acetylene.

32. What is the major component of permanent type antifreeze for automobile cooling system?

(a) Glycerol

(b) Methanol

(c) Picric acid

(d) Ethylene glycol

Explanation; (d)

Ethylene glycol is the major component of permanent type antifreeze for automobile cooling system

33. Propylene oxide is isomeric with: 

(a) Propanoic acid

(b) Propanone

(c) Propene

(d) Propanol

Explanation; (b)

Propylene oxide is in fact an epoxide which is isomeric with ketone having general formula CnH2nO. Epoxides are also isomeric with aldehyde and alkenol.

34. How many isomeric alcohols can be obtained from C₄H₉OH?

(a) 2 

(b) 3

(c) 4 

(d) 5

Explanation; (c)

C₄H₉OH is butyl alcohol containing butyl radical which has 4 isomeric forms, so this alcohol also has 4 isomers. 

35. How many esters are there with the molecular formula C₄H₈O₂?

(a) 2 

(b) 3 

(c) 5 

(d) 4

Explanation; (d)

Since molecular formula, C₄H₈O₂ obeys general formula C_nH_2nO₂, so possible isomers should belong to carboxyl acids and esters. There are 4 isomers esters possible for the molecular formula C₄H₈O₂

36. Sodium or potassium salts of aryl or alkyl sulphonated acids are called:

(a) Soap(b) Detergents(c) Fatty acids

(d) Glass

Explanation; (b)

Sodium or potassium salts of aryl or alkyl sulphonated acids are called detergents. 

37. The general formula for ethers is:

(a) C_nH_{2n +2} O

(b) (C_nH_{2n +1})₂O

(c) C_nH_2n+1O

(d) Both a and b

Explanation; (d)

The general formula for ethers is:

C_nH_{2n +2} O

(C_nH_{2n +1})₂O

C_nH_{2n +1}O C_nH_{2n +1}

38. The most productive distillate of coal is

(a) Ammonical liquor

(b) Coal gas

(c) Coke

(d) Coal tar 

Explanation; (a)

The most productive distillate of coal is Coal tar.

39. In Bucky balls the smallest molecule known contains ……….. carbon atoms

(a) 70

(b) 60

(c) 20

(d) 30 

Explanation; (b)

In Bucky balls the smallest molecule known contains 60 carbon atoms.

40. All elements given below can be detected in an organic compound without using Lassaigne’s solution except

(a) Carbon 

(b) Hydrogen 

(c) Oxygen 

(d) Nitrogen 

Explanation; (d)

Nitrogen is detected by using Lassaigne’s solution.

41. When lime water turns milky, it shows the presence of …………..in the organic compound. 

(a) CO₂

(b) O₂

(c) H₂O

(d) Carbon 

Explanation; (d)

When lime water turns milky due to formation of calcium carbonate showing that addition of carbon in the form of carbon dioxide which must come from carbon in the organic compound.  

42. Which observation confirms sulphur in the organic compound when Lassaigne’s solution is reacted with specific reagent?

(a) Prussian blue ppt

(b) Deep yellow ppt

(c) Black ppt

(d) White ppt

Explanation; (c)

Black ppt of PbS confirms the presence of sulphur in the organic compound when Lassaigne’s solution is reacted with lead acetate. 

43.  Lassaigne’s solution is reacted with reagents like HNO₃ and AgNO₃ to detect ………. in the organic compound

(a) N

(b) S

(c) O 

(d) Br

Explanation; (d)

The presence of Br is confirmed using reagents like HNO₃ and AgNO₃

44.   The IUPAC name for sec-butyl alcohol is

(a) Butan-2-ol

(b) 2-ethylbutan-1-ol

(c) Butan-1-ol

(d) 2-ethylbutan-1-ol

Explanation; (c)

In secondary alcohols, - OH group is present at carbon number 2. Hence sec-butyl alcohol is called butan-2-ol. 

45. The IUPAC name for H₂C=CH – CH = CH₂ is 

(a) Buta-1,3-diene

(b) Pent-1-en-3-yne

(c) But-1-en-3-yne

(d) Penta-1,3-diene

Explanation; (c)

The compounds containing two double bonds are called alkadiene. 

46.  Which one is ethonoic anhydride?

(a) CH₃ – COO – CH₂CH₃

(b) CH₃ – CO– O – OC – CH₃

(c) CH₃ – COO – CH₃

(d) CH₃ – CO – CH₃ 

Explanation; (b)

Anhydride literally means ‘without water. It can be defined as the chemical compound usually oxide formed by eliminating water from another compound. Anhydride reacts with water to produce either base or an acid, so accordingly they may be categorized as acid anhydride and basic anhydride.

An Acid anhydride can be defined as a non-metal oxide which forms an acidic solution when reacted with water. The non-metals which are capable of reacting with water are only called Acid anhydrides and non-metals that do not react with water are not acids anhydrides.

So we can conclude that all non-metals are not acid anhydride; those non-metals that react with water from acid are only acid anhydride. For example, carbon monoxide is not an acid anhydride, though it is an oxide of carbon because it does not react with water.

In organic chemistry, acid anhydride is a functional group consisting of 2 acyl groups combined by an oxygen atom. In the case of organic chemistry, acid anhydrides are formed from the dehydration of two carboxylic acid groups. Alkanoic anhydride/carboxylic anhydride are formulated as (RCO)₂O.

 

47.  The structural formula of methyl ethanonate is

(a) CH₃ – COO – CH₃

(b) CH₃ – OOC – CH₃

(c) CH₃ – CO – OH

(d) Both a and b

Explanation; (d)

48.  The IUPAC name of H – CO – NH₂ is

(a) Formamide

(b) Methanamide

(c) Acetamide

(d) Ethanamide

Explanation; (b)

The IUPAC name of containing amide group is alkanamide. The common name of amide is carboxamide. 

49. Propanoyl chloride is a member of

(a) Acid amides

(b) Acid halides

(c) Acid anhydride

(d) Alkyl halides

Explanation; (b)

Propanoyl chloride is a member of Acid halides.

50.  Which one is organic compound?

(a)  KCN

(b) CS₂

(c) NH₄OCN

(d) None of these

Explanation; (d)

Metallic cyanides, cyanates, thiocynates, carbonates, bicarbonates, carbides, dicarbides, oxides of carbon like CO, CO₂, C₃O₂, and carbon disulphide are inorganic compounds. All given compounds are inorganic compounds. 

51. Lassaigne’s solution is also called

(a) Bromine water

(b) Sodium extract

(c) Copper extract

(d) Nickel extract

Explanation; (b)

Lassaigne’s solution is also called Sodium extract.

52. Which element is not detected in organic compound?

(a) Carbon 

(b) Hydrogen

(c) Oxygen

(d) Nitrogen

Explanation; (c)

Oxygen cannot be detected in organic compounds directly. 

53. A liquid alkane may be converted into gaseous hydrocarbon by

(a) Oxidation

(b) Reduction

(c) Cracking

(d) Hydrolysis

Explanation; (c)

Cracking is used to covert liquid alkane of long chain hydrocarbon to gaseous hydrocarbon of smaller chain. Lower alkanes are gaseous in nature while higher alkanes are either liquids or solids. 

54.  We use (C₂H₅)₄Pb in the gasoline to reduce

(a) Consumption of fuel

(b) Price of fuel

(c) Octane number of fuel

(d) Knocking of engine

Explanation; (d)

(C₂H₅)₄Pb is an anti-knock agent that reduces of knocking of engine. 

55. When n-octane is heated in the absence of air at high temperature in the presence of catalyst, it changes to 2,2,4-trimethylpentane. This process is called

(a) Polymerization

(b) Condensation

(c) Reforming

(d) Cracking

Explanation; (c)

Reforming is the conversion of normal-alkane or straight chain alkanes into isomeric branched chain alkanes. 

56.  Which of the following is cycloalkane?

(a) C₆H₁₄

(b) C₆H₁₂

(c) C₆H₁₀

(d) C₆H₈

Explanation; (b)

Cycloalkanes have general formula C_nH_2n (n=3-infinity). Here C₆H₁₂ obeys the general formula. 

57. Which isomers have difference in both their physical and chemical properties?

(a) Skeletal isomers

(b) Positional isomers

(c) Metamers

(d) Functional isomers

Explanation; (d)

Functional isomers have different chemical properties due to different functional groups. Functional isomers also have different physical properties. 

58. The isomerism exhibited by C₅H₁₁OH is

(a) Positional isomerism

(b) Functional isomerism

(c) Chain isomerism

(d) All of these

Explanation; (d)

The molecular formula C₅H₁₁OH belongs to alcohol which can show all the three types of isomerism. 

59. Which isomerism is NOT shown by alkene?

(a) Chain isomerism

(b) Metamerism

(c) Geometrical isomerism

(d) Position isomerism

Explanation; (b)

Alkenes can show chain isomerism (different longest chain but same formula), position isomerism (substituents at different places) and geometrical isomerism (cis-trans) but not metamerism, because it does not contain any functional group like two alkyl groups on either side (R−O−R′).

Metamerism is due to presence of different alkyl groups attached to the same polyvalent functional group or atom. This kind of isomerism is not possible in case of alkenes.

60. Which type of isomerism is being exhibited by FCH=CHF?

(a) Chain isomerism

(b) Structural isomerism

(c) Geometrical isomerism

(d) Position isomerism

Explanation; (c)

FCH=CHF has double bond in which each carbon is surrounded by two different groups. All the two conditions allow this compound to show geometrical isomerism.

(a) 
(b) 
(c) 
(d)

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