HSC Chemistry Question Thread

[Aaron12038488]

Hi jake,

I just went to your chemistry HSC lecture last week - i thought it was great.

Im just a little confused on what is a polymer, monomer and a radical.

Thanks,
Ben

Monomer: A relatively simple molecule from which a polymer can be made.
Polymer: A large molecule in which one or more monomers are repeated.
 a radical (more precisely, a free radical) is an atom, molecule, or ion that has an unpaired valence electron.

[MisterNeo]

Im just a little confused on what is a polymer, monomer and a radical.

A monomer is the repeating unit of a polymer. A polymer is a really long chain made of repeating monomers.

A free radical is an atom that has an unpaired electron. For example, carbon will always want to have 4 bonds with other atoms because of the octet rule (it thinks it has 8 electrons). If carbon had only 3 bonds, then that molecule will be a free radical and is very reactive, as carbon will want get that bond to obtain stability. It is often written in chemical equations with a dot after it, like: CH₃•

[roygbivmagic]

Hi! If a question asks "describe the formation of ethanol for fuel from biomass", can you just answer it by going through the steps:
cellulose -> acid hydrolysis -> glucose -> fermentation -> ethanol
Or are you supposed to talk about the whole sugar cane process? (i.e. the industrial production of ethanol from sugar cane dot point?)
And in general, when are you supposed to talk about the sugar cane process of forming ethanol? Is it only if the question specifically asks for 'sugar cane'?
Thanks!

[MisterNeo]

Hi! If a question asks "describe the formation of ethanol for fuel from biomass", can you just answer it by going through the steps:
cellulose -> acid hydrolysis -> glucose -> fermentation -> ethanol
Or are you supposed to talk about the whole sugar cane process? (i.e. the industrial production of ethanol from sugar cane dot point?)
And in general, when are you supposed to talk about the sugar cane process of forming ethanol? Is it only if the question specifically asks for 'sugar cane'?
Thanks!

hey
I would mention the sugar cane process in the extraction of cellulose step because the question has the key word "biomass", so you must specifically address how it can be obtained from biomass by providing examples. There are a wide range of plants that produce cellulose (corn, sugar canes, rice, etc), and by mentioning sugar cane specifically, it shows the marker that you know your stuff.
If the question asks about the production of ethanol from biomass or its suitability as an alternative to fossil fuels, then I would definitely mention the sugar cane process.

[Azurelies]

(Image removed from quote.)
The absorption is proportionate to the concentration, so you can just divide 10ppm by 4 then multiply by 5 to get the absorbance for 0.500.
Parts per million is the same as mg/L, and you can find mol/L using copper molar mass. Then divide the mol/L by 10 to get the moles in 100mL, and it’s just stoichiometry from there. (Image removed from quote.)
This is what I got, not sure if correct so answers would be nice. Since they give you the NaCl data, I’d assume it plays a role in the calculations because Na⁺ initial concentrations would be increased. You would find the initial concentrations, then work backwards with the K values to find the concentration of bicarbonate and carbonate. The given pH can be converted into H⁺ using 10^(-pH).

Thank you!

[itssona]

heeya
kinda confused; so basically we use cracking to get ethylene? but in some places it says that we crack to get petrol but it can't just be petrol...

can we form petrol from ethylene? which fractions do we crack? I know we cracked heavy molecules but which fractions of crude oil??

thank you

[Natasha.97]

heeya
kinda confused; so basically we use cracking to get ethylene? but in some places it says that we crack to get petrol but it can't just be petrol...

can we form petrol from ethylene? which fractions do we crack? I know we cracked heavy molecules but which fractions of crude oil??

thank you

Hi!

Yes, cracking is process used to get ethylene. Fractionally distillation of petroleum results in fractions such as Refinery gas, gasoline, naptha, LPG, and heavy fuel oils. Most of these fractions aren't in as high demand as ethylene, so cracking (steam/thermal and catalytic) of some of the fractions (namely naptha and LPG) would produce ethylene.

Hope this helps

[itssona]

Hi!

Yes, cracking is process used to get ethylene. Fractionally distillation of petroleum results in fractions such as Refinery gas, gasoline, naptha, LPG, and heavy fuel oils. Most of these fractions aren't in as high demand as ethylene, so cracking (steam/thermal and catalytic) of some of the fractions (namely naptha and LPG) would produce ethylene.

Hope this helps

ohh that makes sense, thank you so much!!!

[Iminschool]

Hey guys, could somebody please share their best tree diagram for the identification of cations and anions.
Thanks

[itssona]

heey if i wanna draw 2 3 dimethyl 2 butene

so do I draw butene and a double bond in the middle and then i add CH3 to the second and third carbon? can someone show a pic please

[Natasha.97]

Hey guys, could somebody please share their best tree diagram for the identification of cations and anions.
Thanks

This is how I remember them

heey if i wanna draw 2 3 dimethyl 2 butene

so do I draw butene and a double bond in the middle and then i add CH3 to the second and third carbon? can someone show a pic please

Yep! Here is a pic:



Hope this helps

[winstondarmawan]

Hello!
Would appreciate help with the MC questions:
2. https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/22396488_1346167522175434_333891129_o.png?oh=f2bf961b52984c47ee8bb3d9cda05a4a&oe=59DD9713
4. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/22385082_1346167608842092_1024465893_n.png?oh=b619ab38e782503b5f93464ac538d3ec&oe=59DE027C
18. https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/22396679_1346168335508686_1796698340_o.png?oh=f9b1e9dff4bac82883afc9bc7fea8200&oe=59DDA77F
Thanks in advance!

[Iminschool]

Hello!
Would appreciate help with the MC questions:
2. https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/22396488_1346167522175434_333891129_o.png?oh=f2bf961b52984c47ee8bb3d9cda05a4a&oe=59DD9713
4. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/22385082_1346167608842092_1024465893_n.png?oh=b619ab38e782503b5f93464ac538d3ec&oe=59DE027C
18. https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/22396679_1346168335508686_1796698340_o.png?oh=f9b1e9dff4bac82883afc9bc7fea8200&oe=59DDA77F
Thanks in advance!

For Q.2, the answer is D as all those substances are acidic
For Q.4 the answer is D as it is unsaturated

Mod edit: Merged posts, please use the “Modify” button at the top right to avoid chain posting

[Savas_P]

Hello!
Would appreciate help with the MC questions:
2. https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/22396488_1346167522175434_333891129_o.png?oh=f2bf961b52984c47ee8bb3d9cda05a4a&oe=59DD9713
4. https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/22385082_1346167608842092_1024465893_n.png?oh=b619ab38e782503b5f93464ac538d3ec&oe=59DE027C
18. https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/22396679_1346168335508686_1796698340_o.png?oh=f9b1e9dff4bac82883afc9bc7fea8200&oe=59DDA77F
Thanks in advance!

for question 18 have no idea but I am guessing you would add HCl to make the conditions acidic and shift it to the right.

[Natasha.97]

Hello!
18. https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/22396679_1346168335508686_1796698340_o.png?oh=f9b1e9dff4bac82883afc9bc7fea8200&oe=59DDA77F
Thanks in advance!

Hi!

The answer would be D (HCl and H₂O):
- The addition of HCl, as Savas_P pointed out, would make the conditions acidic. According to LCP, the reaction would shift to the right to favour the forward reaction (and the formation of HOCl) as the OH^- will neutralise the HCl
- The addition of H₂O (one of the reactants) will also favour the formation of HOCl: The equilibrium will shift to minimise the change, which in this case, will favour the forward reaction ('uses up' the additional water)

Hope this helps