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Step-by-Step Explanation
Step 1: Identify the Reactants and Products
The reaction given is a mixture of potassium chlorate (KClO3), oxalic acid (C2H2O4), and sulfuric acid (H2SO4) being heated. The final products formed include potassium sulfate (K2SO4), carbon dioxide (CO2), potassium chloride (KCl), and water (H2O):
KClO3 + C2H2O4 + H2SO4 → K2SO4 + CO2 + KCl + H2O
Step 2: Determine the Oxidation States in the Reactants
Potassium (K) in KClO3 is +1.
Chlorine (Cl) in KClO3: Let the oxidation state of Cl be x.
Since K is +1 and each oxygen (O) is -2, the sum of oxidation states must be 0:
$+1 + x + 3(-2) = 0$
Hence, $x - 5 = 0 \Rightarrow x = +5.$
Carbon (C) in oxalic acid (C2H2O4): Let the oxidation state of C be x.
Each hydrogen (H) is +1, and oxygen (O) is -2. For one molecule,
$2x + 2(+1) + 4(-2) = 0$
$2x + 2 - 8 = 0 \Rightarrow 2x = 6 \Rightarrow x = +3.$
So each carbon is +3.
Sulfur (S) in H2SO4 is +6.
Step 3: Determine the Oxidation States in the Products
Potassium sulfate (K2SO4): K is +1, S is +6, O is -2.
Carbon dioxide (CO2): C is +4, O is -2.
Potassium chloride (KCl): K is +1, Cl is -1.
Water (H2O): H is +1, O is -2.
Step 4: Compare Changes in Oxidation States
The key changes to note:
Chlorine changes from +5 in KClO3 to -1 in KCl.
Carbon changes from +3 in C2H2O4 to +4 in CO2.
The change in chlorine’s oxidation state is from +5 to -1, which is a decrease of 6 units. Meanwhile, carbon’s oxidation state changes by +1 (from +3 to +4). Obviously, the 6-unit change in chlorine’s oxidation state is larger.
Step 5: Conclusion
The element undergoing the maximum change in oxidation number during this reaction is chlorine (Cl), going from +5 to -1.
