chemistry : class12 Structure of Pentathionic Acid : Structures of oxoacids of sulphur : p-Block Elements MCQ Questions and Answers
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Structure of Pentathionic Acid
MCQ questions and answers.
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MCQ Questions
1. Which condensed structural formula correctly represents pentathionic acid?
A.
HO3S-S-S-S-SO3H
B.
HO3S-S-S-S-S-SO3H
C.
HO3S-S-S-SO3H
D.
HO-S(=O)-S-S-S-S(=O)-OH
Correct Answer:
HO3S-S-S-S-SO3H
Explanation:
Pentathionic acid is H2S5O6 and has two terminal sulfonic acid groups joined by a chain containing three intervening sulfur atoms. Its structure is written as HO3S-S-S-S-SO3H.
2. In the structure of pentathionic acid, how many sulfur atoms are directly bonded to oxygen atoms?
A.
One
B.
Two
C.
Three
D.
Five
Correct Answer:
Two
Explanation:
The structure HO3S-S-S-S-SO3H contains two terminal sulfur atoms, each bonded to three oxygen atoms in a sulfonic acid group. The three internal sulfur atoms are bonded only to sulfur atoms.
3. What is the number of sulfur-sulfur bonds in one molecule of pentathionic acid?
A.
Two
B.
Three
C.
Four
D.
Five
Correct Answer:
Four
Explanation:
Pentathionic acid contains a continuous chain of five sulfur atoms. A linear chain of five sulfur atoms has four S-S linkages, represented by HO3S-S-S-S-SO3H.
4. Which set gives the oxidation states of the sulfur atoms in pentathionic acid, distinguishing terminal and internal sulfur atoms?
A.
Terminal sulfur atoms: +5 each; internal sulfur atoms: 0 each
B.
Terminal sulfur atoms: +6 each; internal sulfur atoms: -1 each
C.
Terminal sulfur atoms: +4 each; internal sulfur atoms: +1 each
D.
Terminal sulfur atoms: +3 each; internal sulfur atoms: +2 each
Explanation:
Each terminal sulfur is bonded to three oxygen atoms and therefore has oxidation state +5. The three internal sulfur atoms are connected only through S-S bonds, which do not produce oxidation-state differences, so each is assigned oxidation state 0.
5. Which statement correctly describes the two terminal groups in pentathionic acid?
A.
They are two terminal sulfide groups, each bonded to one hydrogen atom.
B.
They are two terminal sulfate groups, each bonded to four oxygen atoms.
C.
They are two terminal sulfonic acid groups, each containing one S-OH bond and two S=O bonds.
D.
They are two terminal sulfite groups, each containing one S-OH bond and one S=O bond.
Correct Answer:
They are two terminal sulfonic acid groups, each containing one S-OH bond and two S=O bonds.
Explanation:
Pentathionic acid has the structure HO3S-S-S-S-SO3H. Each terminal sulfur forms a sulfonic acid unit, conventionally represented as -S(=O)2-OH, attached to the sulfur chain.
6. The molecular formula H2S5O6 of pentathionic acid is most directly explained by which structural atom count?
A.
Two hydroxyl hydrogens, six oxygens, and five sulfur atoms
B.
Six hydroxyl hydrogens, two oxygens, and five sulfur atoms
C.
Two hydroxyl hydrogens, five oxygens, and six sulfur atoms
D.
One hydroxyl hydrogen, six oxygens, and five sulfur atoms
Correct Answer:
Two hydroxyl hydrogens, six oxygens, and five sulfur atoms
Explanation:
The molecule contains five sulfur atoms in the chain, six oxygen atoms in the two -SO3H groups, and two hydrogen atoms, one on each terminal hydroxyl group.
7. If the sulfur chain in pentathionic acid is represented as -S-S-S-S-S-, which sulfur atoms in this chain carry the hydroxyl groups?
A.
The first and second sulfur atoms
B.
The second and fourth sulfur atoms
C.
The first and fifth sulfur atoms
D.
The third and fifth sulfur atoms
Correct Answer:
The first and fifth sulfur atoms
Explanation:
The two terminal sulfur atoms are bonded to the -OH-containing sulfonic acid groups. Thus the first and fifth sulfur atoms in the five-sulfur chain are the oxygen-bearing terminal atoms.
8. What is the average oxidation state of sulfur in pentathionic acid?
A.
0
B.
+1
C.
+2
D.
+5
Correct Answer:
+2
Explanation:
For H2S5O6, the oxidation-state sum is 2(+1) + 5x + 6(-2) = 0, giving 5x = 10 and x = +2. This average results from two terminal sulfur atoms at +5 and three internal sulfur atoms at 0.
9. Which description of the sulfur-sulfur framework in pentathionic acid is correct?
A.
A cyclic S5 ring bearing two hydroxyl groups
B.
A linear chain of five sulfur atoms with sulfonic acid groups at both ends
C.
A branched sulfur atom bonded to four terminal sulfur atoms
D.
Two separate S2 units connected through a single oxygen atom
Correct Answer:
A linear chain of five sulfur atoms with sulfonic acid groups at both ends
Explanation:
Pentathionic acid belongs to the polythionic acids and has the linear arrangement HO3S-S-S-S-SO3H. The sulfur atoms form an unbranched chain, while the two terminal atoms carry the sulfonic acid groups.
10. Upon conceptual cleavage of the two terminal sulfonic acid groups from pentathionic acid, how many sulfur atoms remain in the central sulfur chain?
A.
Two
B.
Three
C.
Four
D.
Five
Correct Answer:
Three
Explanation:
Pentathionic acid contains five sulfur atoms in total. Two are terminal sulfur atoms belonging to the -SO3H groups, leaving three internal sulfur atoms in the central S-S-S segment.
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