HSC Chemistry Question Thread

[peterpiper]

Hey everyone,
I'm having a bit of trouble with understanding half-equations for compounds. The question below is from an assignment and I can't figure out how to do it.

Describe, using half equations, what happens in the electrolysis of aqueous solutions of sodium sulfate and magnesium nitrate.

Thanks in advance for your assistance 

Isn't it just going to be water reacting with water? Because water is both the strongest reductant and oxidant than the magnesium/sodium ions. I don't know what HSC chemistry is like but with VCE chem we have a databook and what I do is I list them out like:

O2(g) + 4H+ +4e- --> <-- 2H2O(l)                +1.23V
2H2O(l) + 2e- ---> <--- H2(g) + 2OH-(aq)    -0.83V
Mg2+(aq) + 2e- --><--- Mg(s)                      -2.37V
Na+(aq)  + e- ---> <--- Na(s)                        -2.71V

Then I highlight the ions/solids that are in the electrolysis setup, and the ones on the RHS you want the bottom-most; while for the ones on the LHS you want the uppermost. In this case it happens to be both just water as the strongest reductant/oxidant, meaning that if this were to undergo electrolysis then it won't be the actual Mg/Na ions undergoing reduction/oxidation reactions, but the water molecules themselves, as we know that the ions are in aqueous solution. As for the sulfate and nitrate ions, they're spectator ions, so they don't participate in the reaction.

[BatBec]

Isn't it just going to be water reacting with water? Because water is both the strongest reductant and oxidant than the magnesium/sodium ions. I don't know what HSC chemistry is like but with VCE chem we have a databook and what I do is I list them out like:

O2(g) + 4H+ +4e- --> <-- 2H2O(l)                +1.23V
2H2O(l) + 2e- ---> <--- H2(g) + 2OH-(aq)    -0.83V
Mg2+(aq) + 2e- --><--- Mg(s)                      -2.37V
Na+(aq)  + e- ---> <--- Na(s)                        -2.71V

Then I highlight the ions/solids that are in the electrolysis setup, and the ones on the RHS you want the bottom-most; while for the ones on the LHS you want the uppermost. In this case it happens to be both just water as the strongest reductant/oxidant, meaning that if this were to undergo electrolysis then it won't be the actual Mg/Na ions undergoing reduction/oxidation reactions, but the water molecules themselves, as we know that the ions are in aqueous solution. As for the sulfate and nitrate ions, they're spectator ions, so they don't participate in the reaction.

Ohh thank you, that makes so much more sense I was over complicating it and confused myself.

[winstondarmawan]

Hey!
Just a question about the formation of glucose and it's structural diagram.
Is there a simple way to approach and remember it or should it just be rote learned?
EDIT: Also the same question for approaching the batteries topic.

[Natasha.97]

Hey!
Just a question about the formation of glucose and it's structural diagram.
Is there a simple way to approach and remember it or should it just be rote learned?
EDIT: Also the same question for approaching the batteries topic.

Hey!

I personally wrote it out multiple times on a blank piece of paper over and over again until I could remember it

Batteries
- Equations: I did two flashcards for each cell, one for the anode equation, and one for the cathode equation. On the other side, I would have which cell it belonged to. If I couldn't recite it from memory, I would write it out a few more times and try again.
- Cells: I drew up a table with subheadings from the dot-point, and have the information listed out as bullet points.

Tip: Teaching someone else is the best way to memorise and retain information imo!

Hope this helps 

[kiwiberry]

Hey!
Just a question about the formation of glucose and it's structural diagram.
Is there a simple way to approach and remember it or should it just be rote learned?
EDIT: Also the same question for approaching the batteries topic.

This might not make sense but this is the order I draw glucose in to remember it:
- draw the 5 C's and 1 O in a hexagon
- The carbon next to the O will have a CH2OH group connected on top and a H connected on the bottom
- The carbon directly under this carbon will have a OH connected on top and a H on the bottom
From there on, the OH's and H's on top alternate on each carbon.

Also, remember to connect the C's to the O in the OH not the H!! Hope this helps

[winstondarmawan]

Hello! Can someone please explain Q2.
https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/21034875_1385184934928928_389610171_o.jpg?oh=12d23e429498dc57bc697f819d77f5da&oe=599DADAE
And also, what are the benefits of using cyclo alkanes and alkenes in the bromine water test?
TIA

[kiwiberry]

Hello! Can someone please explain Q2.
https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/21034875_1385184934928928_389610171_o.jpg?oh=12d23e429498dc57bc697f819d77f5da&oe=599DADAE
And also, what are the benefits of using cyclo alkanes and alkenes in the bromine water test?
TIA

For condensation polymerisation, both monomers have to have a functional group on either end - the only two here are ethylene glycol and oxalic acid.

The cyclo's are used because they liquid at room temperature and pressure, whereas ethene/ethane are gases. They're also colourless, cheap and easy to store

[MisterNeo]

Hello! Can someone please explain Q2.
https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/21034875_1385184934928928_389610171_o.jpg?oh=12d23e429498dc57bc697f819d77f5da&oe=599DADAE
And also, what are the benefits of using cyclo alkanes and alkenes in the bromine water test?
TIA

This 5-bond carbon is really irritating me 

[Shadowxo]

(Image removed from quote.)
This 5-bond carbon is really irritating me 

Didn't you know carbon likes having 10 electrons in its outer shell?
(*Disclaimer: it's a mistake in the diagram, it's only supposed to have 8 electrons / 4 pairs in outer shell)
You know your joke is bad when the disclaimer is longer than the joke

[scienceislife]

I have no idea how to deal with dilution and titration problems so any help with this question would be super helpful. Thank you!

[MisterNeo]

I have no idea how to deal with dilution and titration problems so any help with this question would be super helpful. Thank you!

Hi!
This question asks for moles, so it's just stoichiometry.
-Calculate moles of K₂Cr₂O₇.
0.0144L x 0.03 = 0.000432mol
-Calculate moles of Cr₂O₇^2-.
1:1 mole ratio, so 0.000432mol
-Calculate moles of Sn²⁺.
1:3 mole ratio, so 0.001296mol
-Moles of tin equals moles of tin chloride, so the answer is 1.3 x 10^-3.

[Mymy409]

Is it essential to know how to draw the formation of cellulose? Like showing how the monomers join together to form cellulose?

[Natasha.97]

Is it essential to know how to draw the formation of cellulose? Like showing how the monomers join together to form cellulose?

Hi!

Although the syllabus doesn't specifically say you need to know how to draw it, the dot-point is "Describe the structure of cellulose...", which is essentially an understanding of how the polymer looks like. I would memorise it

[Mymy409]

Hi!

Although the syllabus doesn't specifically say you need to know how to draw it, the dot-point is "Describe the structure of cellulose...", which is essentially an understanding of how the polymer looks like. I would memorise it

Thanks for your reply! Also, if given a diagram of cellulose with three monomers and brackets showing the continuing chain, how many water molecules should we say are released? Are the brackets with bonds reaching out counted as links between monomers or do we only count the ones in inside the brackets - so 2 water molecules?

[Natasha.97]

Thanks for your reply! Also, if given a diagram of cellulose with three monomers and brackets showing the continuing chain, how many water molecules should we say are released? Are the brackets with bonds reaching out counted as links between monomers or do we only count the ones in inside the brackets - so 2 water molecules?

Hi! In this case I'd say that two water molecules were released