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March 19, 2024, 03:12:51 pm

Author Topic: VCE Chemistry Question Thread  (Read 2308923 times)  Share 

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SPQR

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Re: VCE Chemistry Question Thread
« Reply #8100 on: August 14, 2019, 07:01:12 pm »
+1
Looking for advice for practice exams. So for every topic for chem out teacher gives us every single VCAA Q since 2002 for revision, so I have basically done most VCAA Q's. Is it worth starting from VCAA 2002 for full practice exams? Those who scored high 40's, did u do lots of company papers?
i think company papers are a good place to start bc they usually ask more foundational theory-based questions to test whether you've gotten the basic concepts down, and the calculations are nowhere as hard as vcaa. but yeah, vcaa questions are way better so try to move away from company papers.
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bacteriophage

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Re: VCE Chemistry Question Thread
« Reply #8101 on: August 17, 2019, 02:32:55 pm »
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For mass spectroscopy, do we need to know how to write the equation which produces the parent molecular ions and base peaks? (something about bombarding electrons?? - it confuses me!) I saw a question on a VCAA 2010 exam, but not sure if it's within the scope of the new study design...?
And if so, could anyone provide an example of how you would write it?
Thanks
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Re: VCE Chemistry Question Thread
« Reply #8102 on: August 17, 2019, 02:43:37 pm »
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For mass spectroscopy, do we need to know how to write the equation which produces the parent molecular ions and base peaks? (something about bombarding electrons?? - it confuses me!) I saw a question on a VCAA 2010 exam, but not sure if it's within the scope of the new study design...?
And if so, could anyone provide an example of how you would write it?
Thanks
I am not too sure, but you most likely should - I'll quote what it states : "the principles and applications of mass spectroscopy (excluding features of instrumentation and operation) and
interpretation of qualitative and quantitative data, including identification of molecular ion peak, determination
of molecular mass and identification of simple fragments". So I guess you could say yes.


xxxjss

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Re: VCE Chemistry Question Thread
« Reply #8103 on: August 17, 2019, 09:23:35 pm »
+3
For mass spectroscopy, do we need to know how to write the equation which produces the parent molecular ions and base peaks? (something about bombarding electrons?? - it confuses me!) I saw a question on a VCAA 2010 exam, but not sure if it's within the scope of the new study design...?
And if so, could anyone provide an example of how you would write it?
Thanks
Like you said, bombarding electrons... thus electrons must be a reactant! The way I remember how to write the chemical equation of it is that you add one electron and leave with two,and as you leave with more electrons than you added a cation must be produced to balance the charges;
Take example ethanol, CH3CH2OH + e- --> [CH3CH2OH]+ + 2e-
Also, VCAA seems to like having the cation fragment surrounded by [ ] brackets when your asked to write a certain fragment
Whether or not in the scope, I find that at least being exposed to the chemical equation helps clarify what exactly goes on in that funky machine, specifically ionisation  ;D ;D ;D ;D

persistent_insomniac

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Re: VCE Chemistry Question Thread
« Reply #8104 on: August 18, 2019, 08:46:23 pm »
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I just have a qs about reaction rates: if temperature is increased, does it mean that at a certain time t, there is more product produced OR does it mean that at there is the same amount of product but produced faster?

Bri MT

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Re: VCE Chemistry Question Thread
« Reply #8105 on: August 18, 2019, 09:01:21 pm »
+3
I just have a qs about reaction rates: if temperature is increased, does it mean that at a certain time t, there is more product produced OR does it mean that at there is the same amount of product but produced faster?

The same total amount of product is produced and the reaction proceeds at a faster rate.

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Re: VCE Chemistry Question Thread
« Reply #8106 on: August 18, 2019, 09:08:48 pm »
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I just have a qs about reaction rates: if temperature is increased, does it mean that at a certain time t, there is more product produced OR does it mean that at there is the same amount of product but produced faster?
Hey there! To clarify your doubt it means that the amount of product is produced faster. This is due to the law of conservation of matter (Matter can neither be created nor destroyed but only transferred). This is how it  works:
As the temperature increases, the atoms of the product collide with each other rapidly(as atoms gain kinetic energy) , and this results in a reaction. To find reaction rate use arrhenius equation:

rate = k (capital a)^a*(capital b)^b
where rate is in mol dm^-3/s, k is rate constant, A and B are concentrations in mol dm^-3, a is order of reaction in respect to concentration A and b is order of reaction in respect to capital b. 
Edit: I used capital a and b since, it becomes bold when I just write A and B.  :)
« Last Edit: August 18, 2019, 09:14:36 pm by ^^^111^^^ »

jollyboat

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Re: VCE Chemistry Question Thread
« Reply #8107 on: August 19, 2019, 12:17:40 pm »
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Hey guys!

I have a really basic question haha but I can't work it out :(

What type of bond exists between one of the chromium atoms and one of the oxygen atoms in a Cr2O72- polyatomic ion? I was under the impression that all the bonds within polyatomic ions were covalent, however chromium is a metal and oxygen is a non-metal so does that mean that the bond is ionic (since ionic bonds are bonds between 1 metal and 1 non-metal)?
« Last Edit: August 19, 2019, 05:31:20 pm by jollyboat »

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Re: VCE Chemistry Question Thread
« Reply #8108 on: August 19, 2019, 01:39:38 pm »
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Hey guys!

I have a really basic question haha but I can't work it out :(

What type of bond exists between the chromium atom and the oxygen atom in a Cr2O72- polyatomic ion? I was under the impression that all the bonds within polyatomic ions were covalent, however chromium is a metal and oxygen is a non-metal so does that mean that the bond is ionic (since ionic bonds are bonds between 1 metal and 1 non-metal)?
I am pretty sure that it should be an ionic compound. Because, the molecular formula that you have given me is dichromate, and that is an ionic compound. Usually a metal and a polyatomic ion, is almost always an ionic compound. Not too sure, so it would be great if someone else can look at this :)

khai.ling

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Re: VCE Chemistry Question Thread
« Reply #8109 on: August 20, 2019, 06:40:00 pm »
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Hey guys!

I have a really basic question haha but I can't work it out :(

What type of bond exists between one of the chromium atoms and one of the oxygen atoms in a Cr2O72- polyatomic ion? I was under the impression that all the bonds within polyatomic ions were covalent, however chromium is a metal and oxygen is a non-metal so does that mean that the bond is ionic (since ionic bonds are bonds between 1 metal and 1 non-metal)?

Yeah it's ionic but this is waaaaaaay out of the scope of the VCE course - see this link if you want more details.
I hope this isn't a question your school is specifically asking you :/

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Re: VCE Chemistry Question Thread
« Reply #8110 on: August 20, 2019, 08:30:20 pm »
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Yeah it's ionic but this is waaaaaaay out of the scope of the VCE course - see this link if you want more details.
I hope this isn't a question your school is specifically asking you :/
Hahah yes, that's exactly what I was thinking.
Hey guys!

I have a really basic question haha but I can't work it out :(

What type of bond exists between one of the chromium atoms and one of the oxygen atoms in a Cr2O72- polyatomic ion? I was under the impression that all the bonds within polyatomic ions were covalent, however chromium is a metal and oxygen is a non-metal so does that mean that the bond is ionic (since ionic bonds are bonds between 1 metal and 1 non-metal)?
The day you told me the question, I was like researching about ionic and covalent characters. As a thumb rule.  the larger the electronegativity difference, the more "ionic" you could say it is. Vice versa for covalent. To be exact, if the electronegativity is greater than 2, it is considered ionic, if it is less than 1.5, it is considered covalent. Does that help u enough?

pugs

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Re: VCE Chemistry Question Thread
« Reply #8111 on: August 22, 2019, 06:57:32 pm »
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hey guys, this is a v simple question that i have seem to forgotten how to work out :/

how would you convert the concentration of 4% (m/m) ethanoic acid to mol/L or M?
(i've gotten an answer of 0.666..M but not too sure if it's right)

thanks! *pls forgive me*


2019 vce journal here

whys

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Re: VCE Chemistry Question Thread
« Reply #8112 on: August 22, 2019, 11:01:05 pm »
+2
hey guys, this is a v simple question that i have seem to forgotten how to work out :/

how would you convert the concentration of 4% (m/m) ethanoic acid to mol/L or M?
(i've gotten an answer of 0.666..M but not too sure if it's right)

thanks! *pls forgive me*

Molarity = mol solute/L of solution
4% concentration = for every 1000mL (1L), there is 40g ethanoic acid.
Therefore, n(CH3COOH) = mass/molar mass
= 40/60
= 2/3 mol = 0.667 mol
0.667 mol/1L = 0.667 mol/L
= 0.667 M

As per my working out, you are correct! :D
« Last Edit: August 22, 2019, 11:05:16 pm by whys »
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pugs

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Re: VCE Chemistry Question Thread
« Reply #8113 on: August 23, 2019, 06:28:33 pm »
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Molarity = mol solute/L of solution
4% concentration = for every 1000mL (1L), there is 40g ethanoic acid.
Therefore, n(CH3COOH) = mass/molar mass
= 40/60
= 2/3 mol = 0.667 mol
0.667 mol/1L = 0.667 mol/L
= 0.667 M

As per my working out, you are correct! :D
ok thanks so much for the clarification!


2019 vce journal here

Monkeymafia

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Re: VCE Chemistry Question Thread
« Reply #8114 on: August 24, 2019, 04:01:24 pm »
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When finding ΔH values using calorimeters and we get to the 2nd last step as per below:

4.93 x 10^-3 mol C2H2 : 6594.5J
1 mol C2H2 : X J

Do we use 1 mol of C2H2 or 2 mol C2H2 (as per the balanced combustion equation) to find the joules produced in order to find ΔH? Is there a reason for picking one over the other?

Thanks