Carbon and its Compounds Test

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Carbon and its Compounds Test - 2

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Weekly Quiz Competition

Question 1
1 / -0

If the molecular mass of an organic compound is 64 u, what will be the molecular mass of the next homologue of this compound?

A
64 u

B
78 u

C
82 u

D
88 u

Solution

Homologous series is defined as the series of organic compounds having similar chemical characteristics. Two consecutive members differ in their molecular formula by –CH₂ unit or molecular mass of 14 u (12 + 2). The different members of the series are known homologues. Therefore, if the molecular mass of an organic compound is 64 u, the next homologues of this compound will have mass 64 + 14, i.e. 78 u.
Question 2
1 / -0

An alkane has a molecular mass of 72. Its molecular formula is ________.

A
CH₃ - CH₂ - C C - CH₃

B
CH₃ - CH₂ - CH = CH - CH₃

C
CH₃ - CH₂- CH = CH - CH₃

D
CH₃ - CH₂ - CH₂ - CH₂ - CH₃

Solution

Pentane has 5 carbon atoms and 12 hydrogen atoms arranged in its molecular structure.
Molecular mass = 12 × 5 + 1 × 12 = 72
Thus, option 4 is the correct answer.
Question 3
1 / -0

Which of the following series of compounds represents members of a homologous series?

A
CH₄, C₂H₆, C₃H₈

B
C₂H₄, C₃H₆, C₄H₁₀

C
CH₄, C₂H₄, C₃H₈

D
C₂H₄, C₃H₈, C₄H₁₀

Solution

A homologous series is defined as the series of organic compounds having similar chemical characteristics, and whose two consecutive members differ in their molecular formula by a –CH₂ unit or molecular mass of 14 u. CH₄, C₂H₆ and C₃H₈ represent a homologous series because they also differ by a –CH₂ unit. So, they represent a homologous series of alkanes.
Question 4
1 / -0

What is the difference in the molecular masses of two consecutive members of a homologous series?

A
14 u

B
12 u

C
10 u

D
8 u

Solution

A homologous series may be defined as a family of organic compounds having the same functional group, the same chemical properties and the successive members of which differ by a –CH₂ unit. The atomic mass of C is 12 u and that of one atom of H is 1 u. So, the molecular mass of CH₂ becomes 14 u. The adjacent members of homologous series differ in their molecular series by 14 u. For example, CH₄ and C₂H₆ are two consecutive members of the homologous series of alkane. The molecular mass of methane (CH₄) is 16 u, whereas that of ethane (C₂H₆) is 30 u, i.e. they differ in their molecular masses by 14 u.
Question 5
1 / -0

Two consecutive members of a homologous series differ by a __________.

A
-CH₃ unit

B
-CH₂- unit

C
-CH unit

D
unit

Solution

Homologous series is defined as a series of organic compounds having the same chemical characteristics, and whose two consecutive members differ in their molecular formula by a - CH₂ unit or molecular mass of 14 u. For example, CH₄, C₂H₆and C₃H₈ are the members of homologous series for alkane. CH₄ and C₂H₆ differ by a - CH₂ unit. C₂H₆ and C₃H₈ also differ by a - CH₂ unit.
Question 6
1 / -0

Which of the following remain(s) same in a homologous series?

A
Molecular mass

B
Melting point

C
Solubility

D
Chemical properties

Solution

Homologous series is defined as a series of organic compounds having the same chemical characteristics, and whose two consecutive members differ in their molecular formula by a -CH₂ unit or molecular mass of 14 u. For example, if we consider homologous series for alkane, all the members of alkane like methane (CH₄), ethane (C₂H₆), propane (C₃H₈) etc. undergo substitution reactions with halogens.

That is, their chemical properties are the same. The molecular mass of methane is 16 u, and that of ethane is 30 u, i.e. the consecutive members have different molecular masses, and due to the difference in molecular masses, the melting point and other physical properties like solubility are also different.
Question 7
1 / -0

How many unshared electrons are present in an alkyl chain?

A
1

B
2

C
3

D
4

Solution

The removal of one hydrogen atom from the molecule of an alkane gives an alkyl group. Carbon is tetravalent and in alkane, all valencies of carbon are satisfied. If one hydrogen atom is removed from alkane, one electron of carbon will become unshared, i.e. in CH₄, there are four shared pairs of electrons.

If one of the hydrogen atoms is removed, methyl (CH₃) group is formed, in which carbon shares its three valence electrons with three hydrogen atoms, and the fourth valence electron of carbon remains unshared.
Question 8
1 / -0

What is the formula of an alkyl chain with five carbon atoms?

A
C₅H₁₀−

B
C₅H₁₁−

C
−C₅H₁₁−

D
−C₅H₁₀−

Solution

The removal of hydrogen atoms from the molecules of an alkane gives alkyl group. Thus, general formula for alkyl group is C_nH_{2n + 1}, where n = number of carbon atoms. The alkyl group having five carbon atoms will have formula C₅H₁₁–.
Option (3), i.e. –C₅H₁₁– is wrong because alkyl group has only one unshared electron on carbon. So, it can form only one bond.
Options C₅H₁₀– and –C₅H₁₀– do not obey the general formula of alkyl group. So, they are not alkyl groups.
Question 9
1 / -0

Which of the following compounds are two consecutive members of a homologous series?

A
C₂H₅OH and C₄H₉OH

B
CH₃OH and C₂H₅OH

C
CH₃OH and C₃H₇OH

D
CH₃OH and C₄H₉OH

Solution

A homologous series may be defined as a family of organic compounds having the same functional group, the same chemical properties, and the successive members of which differ by a –CH₂ unit. The atomic mass of one atom of C is 12 u and that of one atom of H is 1 u. So, the molecular mass of CH₂ becomes 14 u. So, the adjacent members of a homologous series differ in their molecular mass by 14 u.
In option (2), CH₃OH and C₂H₅OH are the members of a homologous series because they differ by a –CH₂ unit.
Question 10
1 / -0

How are covalent compounds formed?

A
By gain of electrons

B
By loss of electrons

C
By transfer of electrons

D
By sharing of electrons

Solution

Covalent compounds are formed by the sharing of electrons, whereas the compounds which are formed by transfer or gain or loss of electrons are called ionic compounds.
Question 11
1 / -0

In the structure of graphite, two layers are held together by

A
ionic bonds

B
covalent bonds

C
hydrogen bonds

D
weak Van der Waals forces

Solution

The crystal lattice of graphite comprises layers of hexagonal rings of carbon atoms. Although, the carbon atoms within a layer are bonded by strong covalent bonds, in between the layers there exist weak Van der Waals forces of attraction.
Hence, option (4) is the correct answer.
Question 12
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Which of the following statements is/are not true for hydrocarbons?

A
They contain carbon and hydrogen only.

B
They are generally found as mixtures.

C
Lower members of hydrocarbons are solids.

D
All of these

Solution

Hydrocarbons are compounds of carbon and hydrogen only and usually occur in nature as a mixture in the form of petroleum.
The lower hydrocarbons (up to 4 carbon atoms) are gases, those with 5 to 17 carbon atoms are liquids, and higher members of the series are solids.
Thus, the physical state changes from gases to liquid to solid, with increase in the molecular mass.
Hence, the statement in option (3) is incorrect.
Question 13
1 / -0

What is the difference in the number of hydrogen atoms in alkynes and the corresponding alkenes?

A
One

B
Two

C
Three

D
Four

Solution

The general formula of alkenes is C_nH_2n.
The general formula of alkynes is CnH_{2n - 2}.
Hence, alkenes differ from the corresponding alkynes by two hydrogen atoms.
Question 14
1 / -0

The fullerene C₆₀ comprises of hexagonal and pentagonal rings of carbon atoms.

Select the correct option regarding the structure of this molecule.

A
There are 12 hexagonal rings and 20 pentagonal rings.

B
There are 20 hexagonal rings and 12 pentagonal rings.

C
There are 12 hexagonal rings and 12 pentagonal rings.

D
There are 20 hexagonal rings and 15 pentagonal rings.

E
-

Solution

The fullerene molecule comprises of 20 hexagonal rings and 12 pentagonal rings.
Question 15
1 / -0

Which of the following statements regarding isomers are correct?

I. They have the same molecular formula.
II. They are different physical forms of the same element.
III. They have identical physical properties.
IV. They have the same percentage composition.

A
I and II

B
II and III

C
III and IV

D
I and IV

E
-

Solution

Isomers are molecules of the same compound (not element) with the same molecular formula but different structures. Hence, they differ in one or more of their properties.
Since, they have the same molecular formula, the percentage composition is also the same.
Hence, only the statements I and IV are correct.

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Carbon and its Compounds Test - 2

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Carbon and its Compounds Test - 2

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Question 1

64 u

78 u

82 u

88 u

Solution

Question 2

CH3 - CH2 - C C - CH3

CH3 - CH2 - CH = CH - CH3

CH3 - CH2 - CH = CH - CH3

CH3 - CH2 - CH2 - CH2 - CH3

Solution

Question 3

CH4, C2H6, C3H8

C2H4, C3H6, C4H10

CH4, C2H4, C3H8

C2H4, C3H8, C4H10

Solution

Question 4

14 u

12 u

10 u

8 u

Solution

Question 5

-CH3 unit

-CH2- unit

-CH unit

unit

Solution

Question 6

Molecular mass

Melting point

Solubility

Chemical properties

Solution

Question 7

1

2

3

4

Solution

Question 8

C5H10−

C5H11−

−C5H11−

−C5H10−

Solution

Question 9

C2H5OH and C4H9OH

CH3OH and C2H5OH

CH3OH and C3H7OH

CH3OH and C4H9OH

Solution

Question 10

By gain of electrons

By loss of electrons

By transfer of electrons

By sharing of electrons

Solution

Question 11

ionic bonds

covalent bonds

hydrogen bonds

weak Van der Waals forces

Solution

Question 12

They contain carbon and hydrogen only.

They are generally found as mixtures.

Lower members of hydrocarbons are solids.

All of these

Solution

CH₃ - CH₂ - C C - CH₃

CH₃ - CH₂ - CH = CH - CH₃

CH₃ - CH₂- CH = CH - CH₃

CH₃ - CH₂ - CH₂ - CH₂ - CH₃

CH₄, C₂H₆, C₃H₈

C₂H₄, C₃H₆, C₄H₁₀

CH₄, C₂H₄, C₃H₈

C₂H₄, C₃H₈, C₄H₁₀

-CH₃ unit

-CH₂- unit

C₅H₁₀−

C₅H₁₁−

−C₅H₁₁−

−C₅H₁₀−

C₂H₅OH and C₄H₉OH

CH₃OH and C₂H₅OH

CH₃OH and C₃H₇OH

CH₃OH and C₄H₉OH