Organic Chemistry - Unit Test Paper

Question 1

Draw the branched structural formula of the following organic compounds whose IUPAC names are given below.

1. Pent-1-ene
2. But-2-yne
3. 3-methyl pentane
4. 2-methyl-prop-1-ene
5. Pentan-3-ol
6. 1, 1, 2, 2 tetrabromoethane
7. 2-methyl butan-2-ol
8. 2, 2 dimethylpropan-1-ol
9. 2, 2 dimethyl propane
10. 2-bromo-4-chloro pentane

Answer

Pent-1-ene

But-2-yne

3-methyl pentane

2-methyl-prop-1-ene

Pentan-3-ol

1, 1, 2, 2 tetrabromoethane

2-methyl butan-2-ol

2, 2 dimethylpropan-1-ol

2, 2 dimethyl propane

2-bromo-4-chloro pentane

Question 2

Select the correct answer from the choice in brackets.

1. The vapour density of the fifth member of the homologous series of alkanes. [22/36/29]
2. The isomer of pentane which has '1' C atom attached to '4' other C atoms [n-/iso-/neo-] pentane.
3. The IUPAC name of the product of reaction of ethylene with hydrogen bromide, [ethyl bromide/bromoethane/dibromoethane]
4. The IUPAC name of methyl acetylene. [1-butyne/propyne/ethyne]
5. The functional group in ethanoic acid. [aldehydic/carboxyl/hydroxyl]

Answer

1. 36
2. neo-pentane
3. bromoethane
4. propyne
5. carboxyl

Question 3

Give balanced equations for the following conversions:

1. $\text{1,2 dibromoethane} \xrightarrow{\text{A}} \text{Acetylene} \xrightarrow{\text{B}} \text{Silver acetylide}$
2. $\text{Ethanol} \xrightarrow{\text{C}} \text{Ethene} \xleftarrow{\text{D}} \text{Ethyl iodide}$
3. $\text{Bromoethane} \xrightarrow{\text{E}} \text{Ethane} \xleftarrow{\text{F}} \text{Sodium propanoate}$
4. $\text{Sodium ethanoate} \xrightarrow{\text{G}} \text{Marsh gas} \xrightarrow{\text{G}_1} \text{Methanol} \xrightarrow{\text{G}_2} \text{Methanal} \xrightarrow{\text{G}_3} \text{Methanoic acid}$
5. $\text{Sodium acetate + H}_2 \xleftarrow{\text{H}} \text{Acetic acid} \xrightarrow{\text{H}_1} \text{Ethyl ethanoate}$

Answer

1. $\text{1,2 dibromoethane} \xrightarrow{\text{A}} \text{Acetylene}$

$\text{Acetylene} \xrightarrow{\text{B}} \text{Silver acetylide}$

$\underset{\text{ ethyne}}{\text{HC ≡ CH}} + 2\text{AgNO}_3 + 2\text{NH}_4\text{OH} \longrightarrow \underset{\text{Silver Acetylide}}{\text{Ag-C ≡ C-Ag}} + 2\text{NH}_4\text{NO}_3 + 2\text{H}_2\text{O}$

2. $\text{Ethanol} \xrightarrow{\text{C}} \text{Ethene}$

$\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\$

$\text{Ethyl iodide} \xrightarrow{\text{D}} \text{Ethene}$

$\underset{\text{ ethyl iodide}}{\text{C}_2\text{H}_5\text{I}} + \underset{ \text{ alcoholic}}{\text{KOH}} {\xrightarrow{\text{boil}}} \underset{ \text{ ethene}}{\text{C}_2\text{H}_4} + \text{KI} +\text{H}_2\text{O}$

3. $\text{Bromoethane} \xrightarrow{\text{E}} \text{Ethane}$

$\underset{\text{bromoethane}}{\text{C}_2\text{H}_5\text{Br}} + \underset{\text{nascent hydrogen}}{2\text{[H]}} \xrightarrow[\text{alcohol}]{\text{Zn/Cu couple}} \underset{\text{ethane}}{\text{C}_2\text{H}_6} +\text{HBr}$

$\text{Ethane} \xleftarrow{\text{F}} \text{Sodium propanoate}$

$\underset{\text{sodium propanoate}}{\text{C}_2\text{H}_5\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \xrightarrow[300\degree\text{C}]{\text{CaO}} \underset{\text{ethane}}{\text{C}_2\text{H}_6 \uparrow} + \text{Na}_2\text{CO}_3$

4. $\text{Sodium ethanoate} \xrightarrow{\text{G}} \text{Marsh gas}$

$\underset{\text{ sodium acetate}}{\text{CH}_3\text{COONa}} + \underset{\text{sodalime}}{\text{NaOH}} \xrightarrow[300\degree\text{C}]{\text{CaO}} \underset{\text{methane}}{\text{C}\text{H}_4 \uparrow} + \text{Na}_2\text{CO}_3$

Methane to Methanol to Methanal to Methanoic acid

$\underset{\text{ Methane} }{\text{CH}_4} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text{methanol}}{\text{CH}_3\text{OH}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text {methanal}}{\text{HCHO}} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7]{\text{[O]}} \underset{\text{methanoic acid}}{\text{HCOOH}}$

5. $\text{Sodium acetate + H}_2 \xleftarrow{\text{H}} \text{Acetic acid}$

$2\underset{\text{Acetic acid}}{\text{CH}_3\text{COOH}} + 2\text{Na} \longrightarrow \underset{\text{sodium acetate}}{2\text{CH}_3\text{COONa}} + \text{H}_2$

$\text{Acetic acid}\xrightarrow{\text{H}_1} \text{Ethyl ethanoate}$

$\underset{\text{ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} + \underset{\text{Acetic acid}}{\text{CH}_3\text{COOH}} \xrightarrow{\text{Conc. H}_2\text{SO}_4} \underset{\text{ethyl ethanoate}}{\text{CH}_3-\text{COO}-\text{C}_2\text{H}_5} + \text{H}_2\text{O}$

Question 4

Select from the letters A to G the correct answer corresponding to the statements from 1 to 5 :

   A : Ammoniacal CuCl₂
   B : Trichloromethane
   C : Trichloroethane
   D : Bromine soln.
   E : Aqueous KOH
   F : Ethene
   G : Sodalime
   H : Ethanol
   I : Ethyne

1. The organic compound which forms carbon tetrachloride on reaction with chlorine.
2. The reagent which can distinguish between ethene and ethyne.
3. The substance which reacts with bromoethane to give ethanol.
4. The substance which gives bromoethane on reaction with hydrogen bromide.
5. The substance which reacts with acetic acid to give CH₃COOC₂H₅

Answer

1. The organic compound which forms carbon tetrachloride on reaction with chlorine. — B : Trichloromethane
2. The reagent which can distinguish between ethene and ethyne. — A : Ammoniacal CuCl₂
3. The substance which reacts with bromoethane to give ethanol. — E : Aqueous KOH
4. The substance which gives bromoethane on reaction with hydrogen bromide. — F : Ethene
5. The substance which reacts with acetic acid to give CH₃COOC₂H₅ — H : Ethanol

Question 5

Give balanced equations for the following conversions.

1. An alkyne to an alkene.
2. An alkene to an alkane.
3. An alkane to an alcohol.
4. An alcohol to an alkene.
5. A carboxylic acid to an ammonium salt

Answer

1. An alkyne to an alkene:

$\underset{\text{ ethyne [acetylene]}}{\text{H}_2\text{C}_2} + \text{H}_2 \xrightarrow[300\degree\text{C}]{\text{Nickle}} \underset{\text{ethene}}{\text{C}_2\text{H}_4}$

2. An alkene to an alkane:

$\underset{\text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2 \xrightarrow[300\degree\text{C}]{\text{Nickle}} \underset{\text{ethane}}{\text{C}_2\text{H}_6}$

3. An alkane to an alcohol:

$\underset{\text{ ethane}}{2\text{C}_2\text{H}_6} + \text{O}_2 \xrightarrow[200 \text{\degree C}]{\text{Cu tube}} \underset{\text{ethanol}}{2\text{C}_2\text{H}_5\text{OH}}$

4. An alcohol to an alkene:

$\underset{\text{ ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}_2\text{SO}_4\text{[excess]}} \underset{ \text{ethene}}{\text{C}_2\text{H}_4} + \text{H}_2\text{O}\$

5. A carboxylic acid to an ammonium salt :

$\underset{\text{ acetic acid}}{\text{CH}_3\text{COOH}} + \text{NH}_4\text{OH}\longrightarrow \underset{ \text{Ammonium acetate}}{\text{CH}_3\text{COONH}_4} + \text{H}_2\text{O}\$

Question 6.1

Give reasons for the following :

Concentrated sulphuric acid may be added during esterification of acetic acid.

Answer

Reversible reaction may be prevented by using conc. H₂SO₄ when the reaction is about to complete by removing H₂O.

$\underset{\text{ethyl alcohol}}{\text{C}_2\text{H}_5\text{OH}} + \underset{\text{acetic acid}}{\text{CH}_3\text{COOH}} \xrightarrow{\text{Conc. H}_2\text{SO}_4} \underset{\text{ethyl ethanoate}}{\text{CH}_3-\text{COO}-\text{C}_2\text{H}_5} + \text{H}_2\text{O}$

Question 6.2

Give reasons for the following :

Isomers belonging to the same homologous series may differ in physical properties but not in chemical properties.

Answer

As isomers have same general molecular formula and functional group (if any) and only differ in structural formula, hence, they show same chemical properties and differ in physical properties.

Question 6.3

Give reasons for the following :

A given organic compound can be assigned only one name on the basis of the IUPAC system.

Answer

IUPAC is a systematic way of nomenclature of organic compounds that takes into account only one molecular structure of the compound. Hence, it assigns only one name to the compound.

Question 6.4

Give reasons for the following :

Substitution reactions are characteristic reactions of saturated organic compounds only.

Answer

In saturated hydrocarbons, all the four valencies of each carbon are satisfied by the hydrogen atoms, forming single covalent bond. The non-availability of electrons in the single covalent bond makes them less reactive and therefore undergo characteristic substitution reaction only. Addition reactions are not possible in case of saturated organic compounds.

Question 6.5

Give reasons for the following :

Acetic acid is considered an aliphatic monocarboxylic acid.

Answer

Acetic acid (CH₃ – COOH) contains only one – COOH group (carboxylic acid group) that is why it is called a monocarboxylic acid. As acetic acid does not contain a benzene ring, so it is an aliphatic monocarboxylic acid.