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Author Topic: HSC Chemistry Question Thread  (Read 1040854 times)  Share 

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jakesilove

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Re: Chemistry Question Thread
« Reply #435 on: July 19, 2016, 07:26:04 pm »
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Hey Jake!

I came to the repeat Chem lecture last week at UTS and you showed us this totally boss document that was literally 3 pages of all the reactions we had to memorise, but I forgot where to find it. Can you just let me know where I can find that chemistry bible please? :))

Thanks heaps! :)

You can find it right HERE! Go mental :)

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marynguyen18

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Re: Chemistry Question Thread
« Reply #436 on: July 19, 2016, 10:58:06 pm »
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hey Jake I went to your ATAR Notes lecture at UTS and i'm still really confused with the HSC 2013 question 23, is there any chance you could re explain it?

onepunchboy

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Re: Chemistry Question Thread
« Reply #437 on: July 19, 2016, 11:19:14 pm »
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Hey can someone explain the answer to this question, i put d but its wrong hehe
Thanks

RuiAce

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Re: Chemistry Question Thread
« Reply #438 on: July 19, 2016, 11:35:11 pm »
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(Image removed from quote.)

Hey can someone explain the answer to this question, i put d but its wrong hehe
Thanks
Have you tried calculating the resultant pH for A and B?

The concentration of H+ is going to go down heaps if you react it with a base.

(Can't see the value on the top right corner to do the calculations)


The dilution just raises the pH by 1

onepunchboy

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Re: Chemistry Question Thread
« Reply #439 on: July 19, 2016, 11:37:21 pm »
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Oh right its 0.01 mol/L

RuiAce

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Re: Chemistry Question Thread
« Reply #440 on: July 19, 2016, 11:45:18 pm »
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Original pH = 2

D) The dilution factor by 10 will change the pH into 3

Take B)

HCl(aq) + NaOH(aq) -> NaCl(aq) + H2O(l)

nHCl initial = 0.1L * 0.01 mol L-1 = 10-3 mol
nNaOH initial = 0.01L * 0.1mol L-1 = 10-3 mol

Everything's going to be reacted. The final solution will be neutral with a pH of 7

(You may want to test out the CaCO3 reaction as well just incase the change in pH is greater. But I doubt it will be.)
« Last Edit: July 20, 2016, 12:01:06 am by RuiAce »

amandali

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Re: Chemistry Question Thread
« Reply #441 on: July 20, 2016, 04:33:24 pm »
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are these the correct and main steps for Solvay process?

RuiAce

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Re: Chemistry Question Thread
« Reply #442 on: July 20, 2016, 05:07:30 pm »
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are these the correct and main steps for Solvay process?
Yep I believe those are correct. Try to have all of those equations memorised.

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Re: Chemistry Question Thread
« Reply #443 on: July 21, 2016, 10:58:34 am »
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How do you do well in the water module?

I'm finding that module really hard and I don't want to drop chemistry in the future. I feel that I don't have that level of understanding in chemistry

Also

1. why does alcohol dissolve in both polar and non polar?
2. Why does water dissolve covalent compounds?

Thanks  ;D

RuiAce

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Re: Chemistry Question Thread
« Reply #444 on: July 21, 2016, 11:05:07 am »
+1
How do you do well in the water module?

I'm finding that module really hard and I don't want to drop chemistry in the future. I feel that I don't have that level of understanding in chemistry

Also

1. why does alcohol dissolve in both polar and non polar?
2. Why does water dissolve covalent compounds?

Thanks  ;D
The first question is more of a production of materials question that draws on knowledge for water.

As a rule of thumb, likes dissolve likes

The hydroxyl group (-OH) can be involved with extensive hydrogen bonding between other O, N and F molecules. Because the -OH is also polar, it also engages in dipole-dipole interactions with other polar molecules.

But the long carbon chain is non-polar. The linear non-polar chain is what will dissolve with other non-polar substances such as alkanes, through dispersion forces.

(Dispersion forces are as a result of one side of the molecule temporarily becoming more polar than the other, thereby forming a dipole. Dipole-dipole interactions happen when there is a permanent dipole going on. Hydrogen bonding is only separate from dipole-dipole interactions because it's much stronger; about 1/10 the strength of an actual covalent bond)

Q2 is wrong. Water dissolves certain covalent compounds. It does not dissolve stuff like methane or propane.
The covalent compounds it dissolves are all polar because water IS a polar molecule

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Re: Chemistry Question Thread
« Reply #445 on: July 21, 2016, 03:59:45 pm »
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The first question is more of a production of materials question that draws on knowledge for water.

As a rule of thumb, likes dissolve likes

The hydroxyl group (-OH) can be involved with extensive hydrogen bonding between other O, N and F molecules. Because the -OH is also polar, it also engages in dipole-dipole interactions with other polar molecules.

But the long carbon chain is non-polar. The linear non-polar chain is what will dissolve with other non-polar substances such as alkanes, through dispersion forces.

(Dispersion forces are as a result of one side of the molecule temporarily becoming more polar than the other, thereby forming a dipole. Dipole-dipole interactions happen when there is a permanent dipole going on. Hydrogen bonding is only separate from dipole-dipole interactions because it's much stronger; about 1/10 the strength of an actual covalent bond)

Q2 is wrong. Water dissolves certain covalent compounds. It does not dissolve stuff like methane or propane.
The covalent compounds it dissolves are all polar because water IS a polar molecule

TBH I find that the water module is a hard module and things are very difficult for me to grasp, especially things like VSPER theory, electron pair geometry, spatial geometry, etc

Is this "like dissolves like" something by definition/convention or is there a reason as to why "like dissolves like"

It says here that water is a polar molecule because of it's shape: http://www.triangularwave.com/a1b1.htm and that one side is positively charged and one side is negatively charged. Why is this? (again is this "by definition")

RuiAce

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Re: Chemistry Question Thread
« Reply #446 on: July 21, 2016, 04:40:36 pm »
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TBH I find that the water module is a hard module and things are very difficult for me to grasp, especially things like VSPER theory, electron pair geometry, spatial geometry, etc

Is this "like dissolves like" something by definition/convention or is there a reason as to why "like dissolves like"

It says here that water is a polar molecule because of it's shape: http://www.triangularwave.com/a1b1.htm and that one side is positively charged and one side is negatively charged. Why is this? (again is this "by definition")
Yes that's correct.

If instead, water were a linear molecule like CO2, there would not be a region for high electron density. Recall that electrons like to exist in pairs. However, like charges are obviously going to repel each other - no pair of electrons wants to hug another pair. So that extra 2 electrons in oxygen (that are not covalently bonded) will make advantage of the molecule being bent, and cluster at the top of the oxygen in H2O instead.

It is more easily shown if I drew a diagram tbh though.


Water does take a bit of effort to make sense out of yeah.

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Re: Chemistry Question Thread
« Reply #447 on: July 21, 2016, 04:46:55 pm »
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Yes that's correct.

If instead, water were a linear molecule like CO2, there would not be a region for high electron density. Recall that electrons like to exist in pairs. However, like charges are obviously going to repel each other - no pair of electrons wants to hug another pair. So that extra 2 electrons in oxygen (that are not covalently bonded) will make advantage of the molecule being bent, and cluster at the top of the oxygen in H2O instead.

It is more easily shown if I drew a diagram tbh though.


Water does take a bit of effort to make sense out of yeah.

Try explaining with this picture: https://www.google.com.au/search?hl=en&biw=1366&bih=667&site=webhp&tbm=isch&q=water+molecule+structure&sa=X&ved=0ahUKEwivhsaR-oPOAhXCHZQKHddwB_0QhyYIIw&dpr=1#imgrc=J0EWfEKYgTnznM%3A

(if this helps obviously)

Edit: I'll redo them

http://www.chem1.com/acad/sci/wat-images/H2O.png
http://study.com/cimages/multimages/16/factsaboutwater_molecularstructureimage2.png
http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/graphics/water.gif
http://witcombe.sbc.edu/water/images/chemistrydipolescicx.jpg

RuiAce

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Re: Chemistry Question Thread
« Reply #448 on: July 21, 2016, 04:53:39 pm »
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Jakeybaby

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Re: Chemistry Question Thread
« Reply #449 on: July 21, 2016, 07:03:11 pm »
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