Iffet's chem questions:

[iffets12345]

From Insight 2009:

the fuel cell has the following features:
* A cermaic solid as its electrolyte, in which oxide ions, O^2-are able to move.
*An anode reaction of H₂(g) + O^2-->H₂O(l) + 2e^-
*Hydrogen gas and oxygen gas are the reactants.
*water is the only product.


b. Give an equation for the reaction that takes place at hte cathode of this cell. States are not required.

the answer says O₂ + 4e^--> 2O^2-. But doesn't it say water is the only product?

[masonnnn]

O^2- ions and ^H+ ions = water

that's sneaky though

[iffets12345]

Where are the H+ ions

[vexx]

add up the two equations, you will see that the O2- cancels each other out so water is the only product.

[iffets12345]

Oh that is sooo gay, how could I have seen that =.=

[Mao]

O^2- produced will enter the electrolyte. (There is a net transport of oxides within the electrolyte)

[stonecold]

Sorry to hijack,

But when doing Ka's, do we need to subtract [H+] from [weak acid] ?

Checkpoints seems to thinks so, but I thought it was negligible so you just leave it...

[iffets12345]

um that depends on the questions.... if they specifically told you amounts of [H+] and [weak acid] then I think u minus.
But if it just said "find ph" you don't. It's kind of like in equilibrium where if they said "0.4 mol remaining of x" u have to figure out Y with stoich
no worries stonecold, I only made this thread cause I couldn't find YOURS

[Souljette_93]

Sorry to hijack,

But when doing Ka's, do we need to subtract [H+] from [weak acid] ?

Checkpoints seems to thinks so, but I thought it was negligible so you just leave it...

i saw that too. i just leave it though, since H+ is small you assume the whole concentration to be there, just as you assume that [H]=[A-] when calculating ka. ( at least, that's what it says on my TSFX book, and i follow their teaching..)

[stonecold]

lol, i couldn't be bothered finding mine so I asked here haha.

I just checked the examiners report for the question, and both were acceptable.

It was VCAA Exam 1 Q7 2005.

[toshibaj]

Stonecold, that question was bothering me too ages ago. Could you link me to it? Q7 on VCAA Exam 1, 2005 gives a different question.

Or you could give me the page number on checkpoints.

Thanks.

[stonecold]

Stonecold, that question was bothering me too ages ago. Could you link me to it? Q7 on VCAA Exam 1, 2005 gives a different question.

Or you could give me the page number on checkpoints.

Thanks.

http://www.vcaa.vic.edu.au/vce/studies/chemistry/exams/05chem1.pdf&embedded=true&chrome=true

[crayolé]

So how come O₂ + 4H⁺ + 4e^- ----> 2H₂O doesnt work as the cathode reaction?
Water is still the only product? :s

[toshibaj]

So how come O₂ + 4H⁺ + 4e^- ----> 2H₂O doesnt work as the cathode reaction?
Water is still the only product? :s

It doesn't have an acidic electrolyte, it has oxide ions instead.

[sajib_mostofa]

So how come O₂ + 4H⁺ + 4e^- ----> 2H₂O doesnt work as the cathode reaction?
Water is still the only product? :s

The electrolyte is a ceramic solid, not acidic.

EDIT: Damnit, got beaten!