VCE Chemistry Question Thread

[LPadlan]

is uv-visible spectroscopy required knowledge?

[AngelWings]

is uv-visible spectroscopy required knowledge?

Just checked page 22 on the VCE Chem Study Design. It only seems to be a Unit 2 thing. Therefore, I'm assuming yes, but it's more assumed knowledge rather than required and likely not going to appear directly in a Chem 3/4 exam, if at all.

[reiinicole]

Hey guys,

Just wondering for a hydrogen-oxygen fuel cell with alkaline electrolyte (see VCAA 2013), why is its max voltage +1.23? If it's E(oxidant) - E(reductant) wouldn't that get you +2.06?

Thanks

[TheInfamousJimsRightHandMan]

Hey guys,

Just wondering for a hydrogen-oxygen fuel cell with alkaline electrolyte (see VCAA 2013), why is its max voltage +1.23? If it's E(oxidant) - E(reductant) wouldn't that get you +2.06?

Thanks

So your two equations are:
O2(g) + 2H2O(l) + 4e– ⇌ 4OH–(aq)                          +0.40
2H2O(l) + 2e– ⇌ H2(g) + 2OH–(aq)                          –0.83
If this is the case, then it's 0.40--0.83=1.23V
I presume you might've got the wrong equations???

[reiinicole]

So your two equations are:
O2(g) + 2H2O(l) + 4e– ⇌ 4OH–(aq)                          +0.40
2H2O(l) + 2e– ⇌ H2(g) + 2OH–(aq)                          –0.83
If this is the case, then it's 0.40--0.83=1.23V
I presume you might've got the wrong equations???

Thank you!!! I was looking at the acidic water equation instead. Thanks again

[QueenSmarty]

Did anyone else find the sample exam to be hard, or am I just getting dumber? 

[messi10]

Did anyone else find the sample exam to be hard, or am I just getting dumber? 

That was the hardest thing ever, the answers don't make any sense... OMG I'm so gonna failing tmrw

[Angelx001]

When would you know to use double arrows for a reaction if it doesn't say it is in equilibrium? Thank you!

[messi10]

When would you know to use double arrows for a reaction if it doesn't say it is in equilibrium? Thank you!

When a weak acid or base is reacting

[Willba99]

When would you know to use double arrows for a reaction if it doesn't say it is in equilibrium? Thank you!

I think you would use equilibrium arrows unless it was a combustion reaction or a reaction involving strong acids/bases. Other then those, most reactions exist in a state of equilibrium

[Angelx001]

When a weak acid or base is reacting

Can you elaborate on this please? so any reaction with carboxylic acid or amine ? How about precipitation reactions, how come they have double arrows?
Thank you

[Syndicate]

Can you elaborate on this please? so any reaction with carboxylic acid or amine ? How about precipitation reactions, how come they have double arrows?
Thank you

precipitation reactions don't require the double arrows (I don't think it's part of the course anyways). As for the acid/base reactions, yes, you require the "double arrows" since there will still be H+ and OH- ions present (think of a pH curve)- I don't think this is part of the course either, but it's good to know anyways. Basically if you have a carboxylic acid, and an amine, it's a acid-base reaction.

[zxcvbnm18]

Amount of sig figs in 200??

[keltingmeith]

Amount of sig figs in 200??

Technically, 1, but 200. (with the decimal point) has 3. But, VCAA won't ask questions like this that are unclear.

[shiba woof woof]

Hey guys...

I haven't touched the biology part of chemistry yet (unit 4 AOS 2), considering i did biology last year. How much of it relates to chemistry?

Thanks