Obtain the balanced equation, using the lowest possible whole numbers, for the redox reaction in acidic solution: CH3OH(aq) + Cr2O72−(aq) → CH2O(aq) + Cr3+(aq) How many H+ appear in the final balanced equation, and which side are they on?
A) 8, reactant side
B) 8, product side
C) 14, reactant side
D) 6, product side
E) 12, reactant side
Answer is A. Please explain step by step.
Cr2O72- + CH3OH ---------------> Cr3+ + CH2O
oxidation : CH3OH -------------> CH2O
reduction : Cr2O72- -------------> Cr+3
1) balance oxidation half reaction
Cr2O72- ------------> 2Cr3+
Cr2O72- -------------> 2Cr3+ + 7H2O
14H+ + Cr2O72- -------------> 2Cr3+ + 7H2O
6e– + 14H+ + Cr2O72- ---------------> 2Cr3+ + 7H2O
balance reduction half reaction :
CH3OH ------------> CH2O
CH3OH -----------> CH2O + 2H+
(CH3OH ------------> CH2O + 2H+ + 2e– ) x 3
3CH3OH --------------> 3CH2O + 6H+ + 6e-
Add the 2 equations, cancelling out the electrons and any other common terms
3CH3OH + 8H+ + Cr2O72- → 2Cr3+ + 7H2O + 3CH2O
so in reactant side 8 H+ appear in the balanced equation.
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