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March 28, 2024, 11:28:08 pm

Author Topic: HSC Chemistry Question Thread  (Read 1040543 times)  Share 

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RuiAce

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Re: Chemistry Question Thread
« Reply #600 on: August 06, 2016, 08:42:42 pm »
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Can you do the second image as well? And continuing that q it says "Justify the conditions used during he Haber synthesis of ammonia - High temperature (reactor) and High pressure". But isn't 400 degrees celsius and 200 atm not that high?
Why not? If you ask me 400 degrees would burn me and 200 atm would easily crush me in a matter of seconds as well. (Keep in mind 1atm is everyday pressure)

The temperature of 400deg C is a moderately high temperature chosen as a compromise to balance out between the need to increase the rate of reaction (high temperatures lead to increased kinetic energy among particles) and forcing the equilibrium to the right (Because the production of ammonia is exothermic, by LCP lower temperatures favour the yield)

Pressure is self explanatory: High pressures favour the yield by LCP since there are fewer moles of gas in the products. However if we excessively increase the pressure though, we risk the glassware breaking and losing everything we have.

sire123

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Re: Chemistry Question Thread
« Reply #601 on: August 06, 2016, 08:57:06 pm »
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Ah u have a point there haha! Nah i just read somewhere it's quite an intermediate temperature and pressure. Then what does it mean Justify use for high temperature (reactor)? Is it talking about the reactants

RuiAce

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Re: Chemistry Question Thread
« Reply #602 on: August 06, 2016, 09:02:40 pm »
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Because since LCP predicts that low temperatures shift the equilibrium to the right, having a higher temperature is counter-intuitive.

amandali

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Re: Chemistry Question Thread
« Reply #603 on: August 07, 2016, 04:04:30 pm »
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[




how to know which one is oxidant and reductant

RuiAce

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Re: Chemistry Question Thread
« Reply #604 on: August 07, 2016, 04:42:40 pm »
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[(Image removed from quote.)


(Image removed from quote.)

how to know which one is oxidant and reductant
Consult your table of standard reduction potentials and observe the relevant Eo values to determine if a reaction will occur.

In beaker 1, zinc is higher on the potentials sheet than acid. In fact, this is just your ordinary metal + acid -> salt + hydrogen gas reaction.

Zn(s) + H2SO4(aq) -> ZnSO4(aq) + H2(g)

Remember that the oxidant (aka oxidising agent) is the one that gets reduced. Using OIL-RIG, we know that reduction is gain, so we identify the species that gained electrons.

The correct answer is H+, because two hydrogen ions gained an electron in the formation of hydrogen gas.


Equation 2 works similarly, however is an example of metal displacement:
Zn(s) + CuSO4(aq) -> ZnSO4(aq) + Cu(s)
« Last Edit: August 07, 2016, 07:57:57 pm by RuiAce »

Skidous

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Re: Chemistry Question Thread
« Reply #605 on: August 07, 2016, 08:06:24 pm »
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[(Image removed from quote.)


(Image removed from quote.)

how to know which one is oxidant and reductant

I know this isn't an answer but I want to know how you got your picture in the post like that
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RuiAce

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Re: Chemistry Question Thread
« Reply #606 on: August 07, 2016, 08:13:14 pm »
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I know this isn't an answer but I want to know how you got your picture in the post like that
You either upload it to imgur or something and copy/paste the [img] code, or you upload it where you write the post - attachments are uploaded below the box you type your message
In her instance, however, she uploaded through Tapatalk.

anotherworld2b

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Re: Chemistry Question Thread
« Reply #607 on: August 08, 2016, 12:43:05 am »
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Hi :D
I have some more chem questions if its okay  :)

I tried q3b but i was unable to get the right answer

For q13 i am not sure how to approach the question 

RuiAce

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Re: Chemistry Question Thread
« Reply #608 on: August 08, 2016, 09:19:37 am »
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Hi :D
I have some more chem questions if its okay  :)

I tried q3b but i was unable to get the right answer

For q13 i am not sure how to approach the question



Q13 has gone way outside what could possibly be asked in the HSC. However, it still seems like nothing more than gravimetric analysis so this is my attempt.

a) Weight loss - According to the data given the hydrated copper sulfate definitely decomposed, but because we're talking about 200oC here, the water most likely got evaporated off.
b) 1.67/4.77 * 100% = 35%(approx) - use mass, not molar mass to find percentage composition here.
c) Error is not in the HSC course.

sire123

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Re: Chemistry Question Thread
« Reply #609 on: August 09, 2016, 01:26:29 pm »
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A q asks "Write the full ground state electron configuration of chromium showing:
- principle shell notation
- sub-shell notation
- orbital notation
How do u do it?

senara

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Re: Chemistry Question Thread
« Reply #610 on: August 11, 2016, 08:58:35 pm »
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Hi Just wondering do we need to know how to draw dry cell and vanadium redox?

jakesilove

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Re: Chemistry Question Thread
« Reply #611 on: August 11, 2016, 10:30:34 pm »
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Hi Just wondering do we need to know how to draw dry cell and vanadium redox?

Hey! It is definitely knowing how to draw your battery, if it is at all simple. Specifically, the Dry Cell is quite easy to draw, so I would recommend having that up your sleeve. Vanadium Redox is slightly more complicated, so you probably don't need to have that down. In reality, you might never use either, so it's like an additional "LOOK HOW MUCH I KNOW!" point that you can use to score some marks
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RuiAce

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Re: Chemistry Question Thread
« Reply #612 on: August 11, 2016, 10:37:46 pm »
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Hi Just wondering do we need to know how to draw dry cell and vanadium redox?
Food for thought: I literally drew out the Gratzell cell in the exam last year to help get my marks. (Dry cell wasn't examined for us.)

Loki98

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Re: Chemistry Question Thread
« Reply #613 on: August 13, 2016, 05:23:55 pm »
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Could someone please explain this question to me please.
The colourless aqueous solution of a white solid sample formed a precipitate with an acidified aqueous solution of lead (II) nitrate. what is the possible identity of the original solution of this sample?
a) copper (II) sulfate
b) Barium chloride
c) Sodium sulfate
d) silver chloride
Could you please explain how you disprove the incorrect options.
Thx =]

RuiAce

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Re: Chemistry Question Thread
« Reply #614 on: August 13, 2016, 05:45:35 pm »
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Could someone please explain this question to me please.
The colourless aqueous solution of a white solid sample formed a precipitate with an acidified aqueous solution of lead (II) nitrate. what is the possible identity of the original solution of this sample?
a) copper (II) sulfate
b) Barium chloride
c) Sodium sulfate
d) silver chloride
Could you please explain how you disprove the incorrect options.
Thx =]
This answer is incomplete. I'll ask that someone else finish it off because I'm not sure how to incorporate the acidification. I've started it off in the meantime

Since we know that all nitrates are soluble, there is no way that the precipitate formed could've involved the nitrate ion.

Hence, we consider substances involving the lead ion Pb2+ which are insoluble. Problem is that both PbSO4 AND PbCl2 are insoluble!

Begin a process of elimination.
D) is the first one to go. This is because AgCl is also insoluble. Since silver chloride is insoluble, it cannot have been the aqueous solution.
A) is the second one to go. The presence of the Cu2+ ion means that the solid would've been blue, when clearly it is white.

The last bit is the hard one.