Methanol can be oxidised by hydrogen peroxide to produce carbon dioxide and water.
aCH3OH + 3H2O2 → CO2 + bH20
What is the value of b when this equation is balanced?
A
3
B
4
C
5
D
6
E
7
Bmat 2014

When I tried to Balance this equation the way balancing a redox reaction, its just got more complicated and wrong. Why shouldn’t I regard it as a redox reaction?

hi
is the answer C)?
(please mention what is the right answer it’s easier for us to help you solve)
i don’t think you needed to solve using the redox half reactions
This is a simpler way:
aCH3OH+ 3H2O2 = CO2 + bH2O
the stochiometric number for CO2 is 1 so there can only be 1 C on both the left and right side
So a = 1
count the number of H
left = 4 + 3 * 2 = 10 H so we’ll place b = 5 to balance out the equation
so b = 5
count the number of O
left = 1 + 3 * 2 = 7 on the right = 2 + 5 = 7 to balance out the equation
so we can confirm b = 5

Thank you for taking the time answering. The answer is indeed C, and I had no trouble solving it once I tried to solve it as a regular balancing equation question. I guess what I’m asking is more about the approach to the question. when I first read the question i noticed they specifically mentioned it is a redox reaction ("Methanol can be oxidised "), therefore I saw this as a keyword indicating I should balance it in a redox way. So i guess my question is how can i know when to balance the reactions in each way…

Hey! So, for the approach, in this case, you should look at it as a regular equation and work from the answers to the question itself, trying to use the numbers provided and see if they work

YES of curse this is clear and no doubt about it. Do you have any tips for how to recognize it?
I understand that its a regular equation, my question is how do you know that before starting solving it? (and thus avoiding time wasting)

. The correct value of a in the balanced equation below is:
5H2C2O4 + a H+ + b MnO4 c CO2 + d Mn+2 + e H2O
A. 2
B. 4
C. 5
D. 6
E. 12
2-
20++

In this Question, i first tried to balance it as a regular equation and it was very long and confusing, and it worked only with trial and eror. It is much simpler to solve it in the way of balancing a redox equation.
Now, in the exam i dont have enought time, confidence, and place on the paper to try it in both ways and see what works. Therefor my question is whether there is a way to know what is the right approach before starting solving the question.

if an equation has H+/H2O/e⁻ you can assume it is redox and solve that way

For the original question you posted, it doesn’t matter what type of reaction it is, redox or otherwise, it is already balanced so it’s easier to just solve the normal way by balancing the amount of elements on either side of the equation