VCE Chemistry Question Thread

[Phenomenol]

Basically just to allow a flow of electrons from one place to another that can be used to power motors etc?

Precisely. If you have one container you will have the spontaneous redox reaction occurring without any harnessing of the electron flow.

[Rieko Ioane]

Hi,

For Q30c)ii) would it be wrong to say to use a "smaller amount of espresso coffee such that it's peak area is within the range of the calibration curve"?

Or do we have to say dilution?

[princessofpersia]

Hi,

For Q30c)ii) would it be wrong to say to use a "smaller amount of espresso coffee such that it's peak area is within the range of the calibration curve"?

Or do we have to say dilution?

hey, not sure which 30cii but..
I think it will be more precise to mention 'diluted.' By saying a 'smaller' amount of coffee (as far as my knowledge goes) that doesn't change the concentration of coffee, which is what peak area correlates to. It like a 1M solution of HCl, no matter if you use 20ml or 40ml it will always be 1M.
 Diluting does change concentration.

[usernameincorrect]

Do we have to know the differences between alkaline and acidic electrolyte in galvanic cells? And how will they affect the cells, like how the reactions will differ etc.?

Also, with the term electrolyte, does that refer to both the contents of the salt bridge and the 2 solutions in the separate cells? Cheers

[sweetcheeks]

Do we have to know the differences between alkaline and acidic electrolyte in galvanic cells? And how will they affect the cells, like how the reactions will differ etc.?

Also, with the term electrolyte, does that refer to both the contents of the salt bridge and the 2 solutions in the separate cells? Cheers

Study design doesn't specifiy acidic or basic. I would learn how to do both, as bases only require one extra step in KOHES (adding hydroxides between H and E step). If anyone is unsure I will happy demonstrate.

Judging by the study design, they don't incorporate the salt bridge as electrolyte, as they have both listed in the cell basics. The electrolyte in this case will be the ions in each of the half cells.

[princessofpersia]

Do we have to know the differences between alkaline and acidic electrolyte in galvanic cells? And how will they affect the cells, like how the reactions will differ etc.?

adding onto sweetcheeks,
for alkaline and acidic the reactions will defer by the reactants in the reactions. Alkaline cells will have OH- reacting, while acidic will have H+ reacting. So, say you have a alkaline battery, you cant have the S(s)^note reducing (0.14v in electrochemical series) because H+ is necessary. On the other hand, in an acidic battery, S(s) will be able to reduce as H+ ions are present.
_Note: S(s) + 2H⁺ (aq) + 2e arrow H₂S(aq)

[usernameincorrect]

Study design doesn't specifiy acidic or basic. I would learn how to do both, as bases only require one extra step in KOHES (adding hydroxides between H and E step). If anyone is unsure I will happy demonstrate.

Judging by the study design, they don't incorporate the salt bridge as electrolyte, as they have both listed in the cell basics. The electrolyte in this case will be the ions in each of the half cells.

Ahh yes I get it now, never heard about the differences between the balancing but did some googling and got it. Also big thanks to princessofpersia!

[Rieko Ioane]

hey, not sure which 30cii but..
I think it will be more precise to mention 'diluted.' By saying a 'smaller' amount of coffee (as far as my knowledge goes) that doesn't change the concentration of coffee, which is what peak area correlates to. It like a 1M solution of HCl, no matter if you use 20ml or 40ml it will always be 1M.
 Diluting does change concentration.

Ah thanks. True.

[Willba99]

Can anyone predict what would reaction would take place when KI(aq), KISO3(aq) and H2SO4 are mixed together in deionised water? I'm designing a experiment for school and I'm trying to make an iodine solution for an iodine-starch titration and the teacher told me these ingredients would create the necessary iodine solution, but I'm not sure what reaction would take place? Cheers

EDIT:
I think this might have something to do with triiodide??

[Phenomenol]

Can anyone predict what would reaction would take place when KI(aq), KISO3(aq) and H2SO4 are mixed together in deionised water? I'm designing a experiment for school and I'm trying to make an iodine solution for an iodine-starch titration and the teacher told me these ingredients would create the necessary iodine solution, but I'm not sure what reaction would take place? Cheers

EDIT:
I think this might have something to do with triiodide??

I'm not an inorganic chemist but I'll give this a go

Firstly I'm assuming you meant KIO_3(aq) as opposed to KISO_3(aq). (hopefully haha)

So I^- has an oxidation state of -1 and the iodine in IO₃^- has an oxidation state of +5. So to generate I₂ (oxidation state 0) in solution I would think that some of I^- would be oxidised at the same time that IO₃^- is reduced, while H₂SO₄ is an acid catalyst to help this process occur (much like the acid in acidified dichromate solution for example).

The I₂ probably associates with I^- to generate the triiodide ions you are describing, which (after some googling) I think appears yellow/red normally but when trapped by starch appears blue/black.

I'm not 100% sure all of the above is entirely correct so ask your teacher when you get the chance to!

[papaya seed]

On the data booklet this year, the density of water is listed as  0.997 g mL^–1, so i was just wondering how that would change calculation questions and the use of formula's on the exam?

[Bri MT]

On the data booklet this year, the density of water is listed as  0.997 g mL^–1, so i was just wondering how that would change calculation questions and the use of formula's on the exam?

When doing q=mcT  you first need to multiply the volume by density to get mass
Likewise for M/m=n 

[QueenSmarty]

Hello everyone!
For some reason, I'm having trouble figuring out what this dot point from the study design is actually asking us to know:
-Comparison of energy transformations occurring in spontaneous exothermic redox reactions involving direct contact between reactants compared with those occurring when the reactants are separated in galvanic

Do they mean the energy transformations like chemical to electrical, etc?

[sweetcheeks]

Hello everyone!
For some reason, I'm having trouble figuring out what this dot point from the study design is actually asking us to know:
-Comparison of energy transformations occurring in spontaneous exothermic redox reactions involving direct contact between reactants compared with those occurring when the reactants are separated in galvanic

Do they mean the energy transformations like chemical to electrical, etc?

Its referring to the ability to utilise the electrical energy from a spontaneous redox reaction. We are all familiar with the Zinc Copper cell, where we use an external circuit between the two half cells to utilise some of the electrical energy from the reaction. If we placed zinc in a copper sulfate solution the same reaction is going to occur but we cannot harness the electrical energy.

[waldo2000]

Hey, this might be a dumb question however... What is respiration? do i need to know about it for the course?
like if i had glucose (any sugar) and yeast in warm water it would undergo fermentation and create ethanol and carbon dioxide right? would it also undergo respiration at the same time? or do i need a certain enzyme for it? i am currently clueless with respiration (I have tried looking it up on google but it was too confusing)
thanks