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Topic: How would you know which will reduce the Cr?  (Read 5566 times)

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Offline Borek

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Re: How would you know which will reduce the Cr?
« Reply #15 on: April 10, 2016, 03:37:51 AM »
Are nitric acid and nitrous acid oxidizing agent(oxidzer) or reducing agent(reductor)?

They are reductants.

No. Nitric acid is a strong oxidizer.

I suppose now you know enough to get back to the original question. Don't be so passive. We are pointing you to important facts, and you know enough to answer the original problem, but you stay where you are waiting to be pushed.
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Offline T

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Re: How would you know which will reduce the Cr?
« Reply #16 on: April 10, 2016, 07:48:20 PM »
I suppose now you know enough to get back to the original question. Don't be so passive. We are pointing you to important facts, and you know enough to answer the original problem, but you stay where you are waiting to be pushed.

A SnCl2 -- Can be oxidised, Sn 2+  :rarrow: 4+ and Cl 1- :rarrow: Cl2

B KI -- Can be oxidised I 1- :rarrow: 12

C CH3CH2OH -- Can be oxidised CH3CH2OH :rarrow: CH3CH2O

D NaNO2 -- Can be oxidised from NO2  :rarrow: NO3

No. Nitric acid is a strong oxidizer.

Is the redox reaction NO3- + 2H+ + e-:rarrow: NO2 + H2O?

E Al2(SO4)3

This shows that A, B, C, and D can all be oxidised so it can all reduce the dichromate ion. This leaves E as the answer. Can someone just check if my reasoning is correct? Also, will B be the one with the murky brown because of the Iodide?

Thanks

Offline AWK

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Re: How would you know which will reduce the Cr?
« Reply #17 on: April 10, 2016, 10:33:59 PM »
OK
AWK

Offline T

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Re: How would you know which will reduce the Cr?
« Reply #18 on: April 10, 2016, 10:39:07 PM »
OK

Does that mean my reasoning is correct?

Offline AWK

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Re: How would you know which will reduce the Cr?
« Reply #19 on: April 11, 2016, 12:20:11 AM »
As I told at beginning, the oxidation numbers are keys to this problem
SnCl2 +2, -1 => +4, 0(Cl2, even more with other oxidizers)
KI;  I -1 => 0 (I2, up to +7)
C2H6O; C -2 (mean value) => up to +4(in CO2)
NaNO2; N +3 => up to +5 (in NO3-)
no ON change in E
Every periodic table contains typical oxidation numbers for all elements.
K, Na, Al, S, H, O - no change in ONs
Note C - ONs for C and H are very close. We always use +1 for H in organic compounds.
If you are familiar with ONs and periodic table the  solution needs less than 1 minute.
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Offline T

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Re: How would you know which will reduce the Cr?
« Reply #20 on: April 11, 2016, 02:51:33 AM »
I see, thank you very much

Offline Borek

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Re: How would you know which will reduce the Cr?
« Reply #21 on: April 11, 2016, 03:03:40 AM »
Is the redox reaction NO3- + 2H+ + e-:rarrow: NO2 + H2O

One of possibilities, yes.
« Last Edit: April 11, 2016, 03:53:47 AM by Borek »
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