I am having a hard time understanding how to solve this question: what substance

Question

I am having a hard time understanding how to solve this question:

what substance is reduced in the following reaction? 4HCl+MnO2 --> Cl2+2H2O+MnCl2

A. Cl in HCL

B. Mn in MnO2

C. H in HCl

D. O in MnO2

How do you assign the oxidation number for Mn? And could you please list the other atoms oxidation numbers so that I may compare with my own answers? I was told Mn is +4, but I am still not understanding how you assigned Mn as +4 on the reaction side.... does this mean that the sum of the oxidation numbers needs to be equal to 0? Please list all steps on how to solve. Thank you!

Explanation / Answer

oxidation state of Mn can't be assumed as it shows variable oxidation state
we need to calculate that

in MnO2
we know that oxidation state of is -2
so to balance charge, oxidation state of Mn is +4

in MnCl2:
we know that oxidation state of is -1
so to balance charge, oxidation state of Mn is +2

since oxidation state of Mn is getting reduced from +4 to +2

so Answer is:
B. Mn in MnO2

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