Standard Potential Question (1 Viewer)

[mandog97]

Really struggling with this question from last year's HSC, please help me!!!!!!!!!!!

What is the standard cell potential for the reaction of 1.0 mol L−1 acidified potassium
dichromate (K2Cr2O7 (aq)) with aqueous sulfur dioxide (SO2 (aq)) under standard
conditions?
(A) 1.20 V
(B) 1.52 V
(C) 2.24 V
(D) 3.20 V

 

[rand_althor]

The acidified potassium dichromate ionises: . As it is acidified, is also present. So, checking the Standard Potential Table, we see that the reaction involving is above that involving . This means the sulfur dioxide is more likely to undergo oxidation, while the potassium dichromate is more likely to undergo reduction.



Therefore, the answer is A.

 

[mandog97]

Thanks heaps!!!!!

 

[unicorn_1698]

The acidified potassium dichromate ionises: . As it is acidified, is also present. So, checking the Standard Potential Table, we see that the reaction involving is above that involving . This means the sulfur dioxide is more likely to undergo oxidation, while the potassium dichromate is more likely to undergo reduction.



Therefore, the answer is A.

hi
but what about the potassium? why dont we include that when working out the standard potential??

 

[BlueGas]

hi
but what about the potassium? why dont we include that when working out the standard potential??

Because the question isn't asking for potassium, it's asking for potassium dichormate and sulfur dioxide.

 

[unicorn_1698]

but in the reduction half equation we're meant to use dichromate, why cant we use the potassium ion? and would that be the case with all similar questions?

 

[porcupinetree]

but in the reduction half equation we're meant to use dichromate, why cant we use the potassium ion? and would that be the case with all similar questions?

The potassium ion has already been oxidised to its (effectively) maximum oxidation state by the acid, hence we can be confident that it won't oxidise again

 

[unicorn_1698]

thank youu!