HSC Chemistry Question Thread

[Mymy409]

This might be a bit of a dumb question, but will I lose marks if a diagram isn't shaded correctly?

[jakesilove]

This might be a bit of a dumb question, but will I lose marks if a diagram isn't shaded correctly?

I would definitely say that you shouldn't lose marks! I don't think I've ever shaded a Chemistry diagram in my life.

[beau77bro]

Hey can someone explain this? It doesn't add up/not balanced so what's the proper - btw this is in the atarnotes

Second one btw

[Shadowxo]

(Image removed from quote.)

Hey can someone explain this? It doesn't add up/not balanced so what's the proper - btw this is in the atarnotes

Second one btw

I think it should just be a single H2O, then it balances correctly

[beau77bro]

I think it should just be a single H2O, then it balances correctly

ohhhh ok thankyou hahaha didnt see that
whats the overall equation of the fuel cell?

[Shadowxo]

ohhhh ok thankyou hahaha didnt see that
whats the overall equation of the fuel cell?

Bit rusty but I believe it would just be adding the equations together
Zn(s) + 2MnO₂(aq) + 2H⁺(aq) + 2e^-   ->   Zn²⁺(aq) + 2e^- + Mn₂O₃(aq) + H₂O(l)
Which reduces down to
Zn(s) + 2MnO₂(aq) + 2H⁺(aq)   ->   Zn²⁺(aq) + Mn₂O₃(aq) + H₂O(l)

[necromantic]

Why does the fermentation of glucose take place under anaerobic conditions? 

[Natasha.97]

Why does the fermentation of glucose take place under anaerobic conditions? 

Hi!

Yeast will only produce ethanol when respiring anaerobically (and as ethanol is the desired product, fermentation must take place without oxygen).

Hope this helps

[MisterNeo]

Why does the fermentation of glucose take place under anaerobic conditions? 

If there was oxygen present during fermentation, the ethanol would get oxidised into acetic acid. Hence, it is done without oxygen.


Also respiration purposes like what Jess said

[beau77bro]

Bit rusty but I believe it would just be adding the equations together
Zn(s) + 2MnO₂(aq) + 2H⁺(aq) + 2e^-   ->   Zn²⁺(aq) + 2e^- + Mn₂O₃(aq) + H₂O(l)
Which reduces down to
Zn(s) + 2MnO₂(aq) + 2H⁺(aq)   ->   Zn²⁺(aq) + Mn₂O₃(aq) + H₂O(l)

yea thats the dry cell what about the fuel cell from the notes? there are waters in both equation and i'm unsure how to deal with it?

[VanillaRice]

yea thats the dry cell what about the fuel cell from the notes? there are waters in both equation and i'm unsure how to deal with it?

I think the image might be a bit cropped, so I can't exactly see that part (or it might just be my computer  )
Either way, I assume that's the hydrogen fuel cell? I'm also going to assume that we're dealing with an alkaline electrolyte (since it involves a few more water molecules).
The equations should be:
ANODE
\(\ce{2H2 + 4OH- -> 4e- + 4H2O}\)
I've doubled the coefficients above so we can directly add it to the equation below:
CATHODE
\(\ce{O2 + 2H2O + 4e -> 4OH-}\)
Therefore adding the equations gives
\(\ce{O2 + 2H2O + 4e + 2H2 + 4OH- -> 4OH- + 4e- + 4H2O}\)
Now to directly address your question, we can simply cancel out the hydroxides and waters (similar to the way we can cancel out electrons)
\(\ce{O2 +  2H2 -> 2H2O}\)

Hope this helps

[smshs2017]

hey can you pls help me with the different type of bonds, for example hydrogen bonds, dispersion, dipole dipole and others, because i keep confusing which is which, and which one is stronger than the other and all that.
thanks!!!!

[MisterNeo]

hey can you pls help me with the different type of bonds, for example hydrogen bonds, dispersion, dipole dipole and others, because i keep confusing which is which, and which one is stronger than the other and all that.
thanks!!!!

Hey
There are two types of bonds/forces: Intramolecular and intermolecular.
-Intramolecular is between atoms in a molecule.
-Intermolecular is between various molecules.

Intra
-Covalent:
An "electron-sharing" bond between non-metals.
Eg. H₂O, O₂, etc.
-Ionic:
A bond between a positively charged cation and a negatively charged anion. The anion keeps the electrons it is given, and the cation loses it. They are usually between a metal and non-metal, BUT not always because ammonium (NH₄⁺) salts are also ionic.
Eg. NaCl, KOH, etc.
-Metallic:
Bonds between metals via delocalised electrons. This is more commonly tested in prelim rather than HSC course.
Eg. Fe, Cu, etc.

Inter
-Hydrogen bonding:
A special type of dipole-dipole bond where a slightly positive hydrogen attracts to a slightly negative atom. The slightly negative atom is usually a highly electronegative element such as oxygen or a halogen (polar), which is bonded to a hydrogen and pulls the electrons closer to itself thus creating the charges.

-Dipole Dipole/Ion Dipole
Very similar to hydrogen bonding Ion dipoles form when ionic molecules are attracted to polar molecules. This is how NaCl dissolves in water. The chloride attracts to the water's positive hydrogen and vice versa with the sodium.

-Dispersion forces:
A bit hard to explain, so this pic explains it. Hydrocarbon chains have stronger dispersion forces.

Hydrogen bond > dipoles > dispersion forces
Hope this helps

[beau77bro]

I think the image might be a bit cropped, so I can't exactly see that part (or it might just be my computer  )
Either way, I assume that's the hydrogen fuel cell? I'm also going to assume that we're dealing with an alkaline electrolyte (since it involves a few more water molecules).
The equations should be:
ANODE
\(\ce{2H2 + 4OH- -> 4e- + 4H2O}\)
I've doubled the coefficients above so we can directly add it to the equation below:
CATHODE
\(\ce{O2 + 2H2O + 4e -> 4OH-}\)
Therefore adding the equations gives
\(\ce{O2 + 2H2O + 4e + 2H2 + 4OH- -> 4OH- + 4e- + 4H2O}\)
Now to directly address your question, we can simply cancel out the hydroxides and waters (similar to the way we can cancel out electrons)
\(\ce{O2 +  2H2 -> 2H2O}\)

Hope this helps

THANKYOU VANILLA RICE

[mjorfian]

Hiii. Just revising biopolymers right now, and I was just wondering, how much of the history do I need to know? I was thinking just the date when it started being produced and whatnot but jake's notes have a whole para on them and its stressing me out because i hate remembering historical detail RIP. does anyone happen to have a short + effective summary on phbs? thanks!