chemistry : class12 Polythionic Acid Structures : Structures of oxoacids of sulphur : p-Block Elements MCQ Questions and Answers
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Polythionic Acid Structures
MCQ questions and answers.
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MCQ Questions
1. Which general structural representation correctly describes a polythionic acid containing n sulfur atoms, where n ≥ 2?
A.
HO3S−S(n−2)−SO3H
B.
H2S−O−S(n−2)−O−S−H
C.
HO−S(=O)2−O−S(n−2)−S(=O)2−OH
D.
H−S(=O)−S(n−2)−S(=O)−H
Correct Answer:
HO3S−S(n−2)−SO3H
Explanation:
Polythionic acids have the chain structure HO3S−S(n−2)−SO3H. The two terminal sulfur atoms belong to sulfonic acid groups, while the intervening sulfur atoms form an unbranched sulfur chain.
2. What is the molecular formula of tetrathionic acid, whose structure is HO3S−S−S−SO3H?
A.
H2S4O4
B.
H2S4O5
C.
H2S4O6
D.
H2S4O8
Correct Answer:
H2S4O6
Explanation:
A polythionic acid with n sulfur atoms has the general formula H2SnO6. Therefore, tetrathionic acid, with four sulfur atoms, is H2S4O6.
3. In the structure of trithionic acid, HO3S−S−SO3H, what are the formal oxidation states of the two terminal sulfur atoms and the central sulfur atom, respectively?
A.
+4, 0, +4
B.
+5, 0, +5
C.
+6, −2, +6
D.
+3, +2, +3
Correct Answer:
+5, 0, +5
Explanation:
In H2S3O6, hydrogen contributes +2 and oxygen contributes −12, so the total oxidation state of sulfur is +10. The two equivalent terminal sulfur atoms are +5 each, leaving the central sulfur at 0.
4. How many sulfur–sulfur bonds are present in a molecule of pentathionic acid, H2S5O6, assuming the normal linear polythionic structure?
A.
2
B.
3
C.
4
D.
5
Correct Answer:
4
Explanation:
A linear chain containing n sulfur atoms has n−1 sulfur–sulfur bonds. Thus, pentathionic acid, with five sulfur atoms, contains four S−S bonds.
5. Which structural feature distinguishes tetrathionic acid from sulfuric acid most directly?
A.
Tetrathionic acid contains two terminal sulfonic groups joined by an S−S−S chain
B.
Tetrathionic acid contains one sulfur atom bonded to four hydroxyl groups
C.
Tetrathionic acid contains only sulfur–oxygen bonds and no sulfur–sulfur bonds
D.
Tetrathionic acid contains a cyclic S4O6 framework without acidic hydrogen atoms
Correct Answer:
Tetrathionic acid contains two terminal sulfonic groups joined by an S−S−S chain
Explanation:
Tetrathionic acid has the structure HO3S−S−S−SO3H. Its characteristic feature is the sulfur chain between two terminal sulfonic acid groups, unlike sulfuric acid, which has only one sulfur atom.
6. For the general polythionic acid structure HO3S−S(n−2)−SO3H, how many sulfur–oxygen bonds are present in the neutral molecule?
A.
2
B.
4
C.
6
D.
2n
Correct Answer:
6
Explanation:
Each terminal sulfonic group, −SO3H, contains three sulfur–oxygen bonds. Since the molecule has two terminal groups, the total number of S−O bonds is six, independent of n.
7. Which pair correctly matches a polythionic acid with its sulfur-chain arrangement?
A.
Dithionic acid: HO3S−S−SO3H
B.
Trithionic acid: HO3S−S−S−S−SO3H
C.
Tetrathionic acid: HO3S−S−S−SO3H
D.
Pentathionic acid: HO3S−S−S−SO3H
Correct Answer:
Dithionic acid: HO3S−S−SO3H
Explanation:
Dithionic acid contains two sulfur atoms and has the structure HO3S−S−SO3H. Trithionic, tetrathionic, and pentathionic acids contain three, four, and five sulfur atoms, respectively.
8. In a linear polythionic acid containing seven sulfur atoms, how many sulfur atoms are formally assigned oxidation state zero in the usual structural oxidation-state description?
A.
2
B.
5
C.
6
D.
7
Correct Answer:
5
Explanation:
The two terminal sulfur atoms belong to the −SO3H groups and are assigned +5. The remaining n−2 sulfur atoms in the chain are assigned oxidation state zero; for n = 7, this gives five internal sulfur atoms.
9. Which statement about the terminal sulfur atoms in polythionic acids is structurally correct?
A.
Each terminal sulfur is bonded to three oxygen atoms and to one sulfur atom
B.
Each terminal sulfur is bonded to two oxygen atoms and to two sulfur atoms
C.
Each terminal sulfur is bonded to one oxygen atom and three sulfur atoms
D.
Each terminal sulfur is bonded only to sulfur atoms and carries both acidic hydrogens
Correct Answer:
Each terminal sulfur is bonded to three oxygen atoms and to one sulfur atom
Explanation:
The terminal groups are −SO3H units. Each terminal sulfur is connected to three oxygen atoms and to the adjacent sulfur atom in the chain; the acidic hydrogen is attached to oxygen, not directly to sulfur.
10. A polythionic acid has the molecular formula H2S6O6. Which combination gives its number of internal sulfur atoms and sulfur–sulfur bonds, respectively?
A.
4 and 5
B.
4 and 6
C.
5 and 5
D.
6 and 4
Correct Answer:
4 and 5
Explanation:
For H2SnO6, there are n−2 internal sulfur atoms and n−1 sulfur–sulfur bonds. With n = 6, the molecule has four internal sulfur atoms and five S−S bonds.
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