Question

A mixture of potassium chlorate, oxalic acid and sulphuric acid is heated. During the reaction which element undergoes maximum change in the oxidation number ?

• A. Cl
• B. C
• C. S
• D. H

Answer 1

The Correct Option is A

To solve this question, we need to determine the element that undergoes the maximum change in oxidation number when a mixture of potassium chlorate (KClO₃), oxalic acid (H₂C₂O₄), and sulfuric acid (H₂SO₄) is heated.

1. First, consider the oxidation state of each element in the compounds:
   • Potassium chlorate (KClO₃):
     • K has an oxidation state of +1.
     • Oxygen (O) typically has an oxidation state of -2.
     • To find the oxidation state of chlorine (Cl), use the formula: (+1) + x + 3(-2) = 0 where x is the oxidation state of Cl.
     • Solving, (+1) + x - 6 = 0 \Rightarrow x = +5.
   • Oxalic acid (H₂C₂O₄):
     • Each hydrogen (H) has an oxidation state of +1, and each oxygen (O) is -2.
     • To find the oxidation state of carbon (C), consider the overall neutrality: 2(+1) + 2y + 4(-2) = 0, where y is the oxidation state of C.
     • Solving, 2 + 2y - 8 = 0 \Rightarrow 2y = 6 \Rightarrow y = +3.
   • Sulfuric acid (H₂SO₄):
     • Each H is +1, each O is -2.
     • For sulfur (S): 2(+1) + z + 4(-2) = 0, where z is the oxidation state of S.
     • Solving, 2 + z - 8 = 0 \Rightarrow z = +6.
2. Now analyze changes upon heating:
   • When KClO₃ is heated, it decomposes to form KCl and O₂.
   • The chlorine changes from +5 in KClO₃ to -1 in KCl (a decrease of 6 units).
   • In oxalic acid, carbon atoms can be oxidized to CO₂, where carbon is in oxidation state +4 (an increase of 1 unit).
3. Considering sulfuric acid, sulfur typically remains in the +6 oxidation state as it typically acts as an oxidizing agent, not reducing.
4. Therefore, chlorine undergoes the maximum change in oxidation number from +5 to -1 in this reaction, which is a decrease of 6 units.

From the above analysis, the element that undergoes the maximum change in oxidation number is chlorine (Cl).