Question 15 of 31advanced🔍 AnalyzeLong Answer5 marks

Consider the reactions: (a) 6 CO₂(g) + 6H₂O(l) → C₆H₁₂O₆(aq) + 6O₂(g) (b) O₃(g) + H₂O₂(l) → H₂O(l) + 2O₂(g) Why it is more appropriate to write these reactions as: (a) 6CO₂(g) + 12H₂O(l) → C₆H₁₂O₆(aq) + 6H₂O(l) + 6O₂(g) (b) O₃(g) + H₂O₂(l) → H₂O(l) + O₂(g) + O₂(g) Also suggest a technique to investigate the path of the above (a) and (b) redox reactions.

Correct Answer

(a) It is more appropriate to write the reaction as 6CO2(g)+12H2O(l)→C6H12O6(aq)+6H2O(l)+6O2(g)6CO_2(g) + 12H_2O(l) \rightarrow C_6H_{12}O_6(aq) + 6H_2O(l) + 6O_2(g) because the oxygen atoms in the evolved O2O_2 gas come entirely from the water (H2OH_2O) molecules, not from carbon dioxide (CO2CO_2). Writing 12 H2OH_2O on the reactant side and 6 H2OH_2O on the product side accurately reflects this mechanistic path and properly balances the hydrogen and oxygen atoms.

(b) It is more appropriate to write the reaction as O3(g)+H2O2(l)→H2O(l)+O2(g)+O2(g)O_3(g) + H_2O_2(l) \rightarrow H_2O(l) + O_2(g) + O_2(g) because the two molecules of O2O_2 produced originate from different reactants. One molecule of O2O_2 is derived from the decomposition of ozone (O3O_3), while the other molecule of O2O_2 comes from hydrogen peroxide (H2O2H_2O_2). Writing them separately illustrates the actual path of the redox reaction.

(technique) The path of these redox reactions can be investigated using the isotopic labeling (or tracer) technique. By using isotopes like H218OH_2^{18}O or H2O218H_2O_2^{18}, we can trace the origin of the oxygen atoms in the evolved O2O_2 gas and determine the exact reaction pathway.

Exercise: EXERCISES | Q: 7.9 | (Page Page 18)
For More Understanding

Explanation

The question tests the understanding of the actual mechanistic path of redox reactions rather than just their stoichiometric balancing. In photosynthesis, isotopic studies prove that the evolved oxygen comes from water, necessitating the use of 12 water molecules. In the reaction between ozone and hydrogen peroxide, the two oxygen molecules come from different sources, which is highlighted by writing them separately. The tracer technique using isotopes is the standard method to investigate such pathways.

Solution Steps

  1. Step 1: For reaction (a), explain that the evolved O2O_2 comes solely from H2OH_2O. Thus, 12 H2OH_2O are required on the reactant side to supply the 6 O2O_2 molecules and the glucose, while 6 H2OH_2O are produced back.

  2. Step 2: For reaction (b), explain that writing O2(g)+O2(g)O_2(g) + O_2(g) separately shows that one O2O_2 molecule is sourced from O3O_3 and the other from H2O2H_2O_2.

  3. Step 3: Suggest the isotopic labeling technique (e.g., using 18O^{18}O isotopes) to trace the path of oxygen atoms and confirm the sources of the evolved gases.

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