destroyer GChem Q

[bkim]

iin Problem 70,

why do we not multiply the final answer given by 2?
In order to find the total change in electrons, I would think that we should take into account that one molecule has two Cr?

Thanks in advance

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[Anemone]

iin Problem 70,

why do we not multiply the final answer given by 2?
In order to find the total change in electrons, I would think that we should take into account that one molecule has two Cr?

Thanks in advance

i dont have the destroyer in front of me, but when youre doing these redox rxn type questions,you never multiply by the number of molecules of whatever it is,present.

 

[bkim]

i dont have the destroyer in front of me, but when youre doing these redox rxn type questions,you never multiply by the number of molecules of whatever it is,present.

Hi there.
Actually it is a normality question, and the solution does multiply the number of the molecules present. It just doesn't take into account that each molecule has two Cr atoms and I am not sure why.

 

[beccaaron]

i think when dealing with oxidation and reduction you dont take the number in front of the element into consideration

in other words- when going from Cr07 -2 -----> Cr +3
you only deal with what the charges would be on those- not including the 2 that would be in front of the Cr+3 after you have balanced it.

if you are not including it- you just simply see what the happens to the Cr, it is reduced from +6 to +3, so there is a change of 3 electrons-


so its the 3 electrons X 2.5M = 7.5



I hope that helps! good luck studying!!

 

[Danny289]

iin Problem 70,

why do we not multiply the final answer given by 2?
In order to find the total change in electrons, I would think that we should take into account that one molecule has two Cr?

Thanks in advance

Hi, dear bkim,
I know you have very good conceputal view of chemistry, i think just we are so overwelmed and nerveous because DAT,( I am almost close to die!).

Ok, just follow my explanation.
back to Normality concept, let me recall that

N= M * n =======> N = Molarite X n

Whats "n" in Oxidation reduction?
i am sure you know that. now back to Dr Romano explanation , the last paragraph !!!? can you see anything except the concept?
when you are heading to balance the oxidation & reduction, you must consider that "2" (you are talking about).
ok , let's explain in another way, again take look the half reaction: whats Cr3+ ? you can find complete version of this reaction in your textbook or any other sources( it is very common example), go find it !
bingo!!! Cr+3 in complete reaction is Cr2O3 !!! I think now you know why we are not considering that "2".
Ok short cut
how about this way : forget half reaction, just approach for "n" without writting and balancing half reaction (oxidation or reduction half reactions), then find N . i must back to work.
hopefully it was helpfull.
Good luck My friend

 

[Dotoday]

Guys it is correct. The problem is correct. I showed it to a chemistry professor and the professor said that it is right.

 

[bkim]

Thanks a lot guys!
You guys are all correct - I have also confirmed it with Dr. Romano.

Thanks again for your great help!