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Author Topic: VCE Chemistry Question Thread  (Read 2313189 times)  Share 

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Just another student

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Re: VCE Chemistry Question Thread
« Reply #8160 on: October 12, 2019, 10:44:30 am »
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Sry my bad, Q is attached.

I don't understand how you get copper in the equation.

thanks

sadia2089

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Re: VCE Chemistry Question Thread
« Reply #8161 on: October 12, 2019, 11:40:38 am »
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For reaction pathways, would all reactants be in liquid form?

Erutepa

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Re: VCE Chemistry Question Thread
« Reply #8162 on: October 12, 2019, 02:55:19 pm »
+3
Sry my bad, Q is attached.

I don't understand how you get copper in the equation.

thanks
What this question wanted you to understand is that some metal ions in the solution were reduced to form a brown metal solid at the cathode. They tell you the metal is brown and they obvously wanted you to infer that this solid metal was copper, thus making the metal ions in solution copper ions. You would then want to use the electrochemical series to identify a oxidation reaction that could occur at the anode which produces a colourless gas which would be oxygen. You would then use the electrochemical series to find the 2 half cell reactions that will occur, remembering that for electrolysis, the reaction with the least negative E° value will occur first.

For reaction pathways, would all reactants be in liquid form?
Not always. Sometimes the reactants are in gas form either becuase they are normally gaseous at slc (methane through to butane are gaseous) or if the reaction occurs with the addition of heat (I.e hydration of alkenes where the reactants will be gaseous) .
If states is what you struggle with, I would recommend drawing up a table with the states of all the different relevant organic compounds and fill it in gradually as you come across them in practice questions.
« Last Edit: October 12, 2019, 03:03:17 pm by Erutepa »
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jnlfs2010

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Re: VCE Chemistry Question Thread
« Reply #8163 on: October 14, 2019, 10:02:21 am »
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Hey, I'm in year 11 this year and in my spare time, I'm studying some chemistry 3/4 and I'm at the end of the course. I've realized VCAA throws a decent amount of experimental theory (like commenting on validity, reliability strengths or weaknesses of experimental design of experiments.....) by providing us with a scientific report from a student. What would be the best way or ways to study this without doing the experiment (I don't think I can!)? Are there some things I could study to assist me with those kinds of questions?
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hums_student

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Re: VCE Chemistry Question Thread
« Reply #8164 on: October 14, 2019, 10:57:49 am »
+2
Hey, I'm in year 11 this year and in my spare time, I'm studying some chemistry 3/4 and I'm at the end of the course. I've realized VCAA throws a decent amount of experimental theory (like commenting on validity, reliability strengths or weaknesses of experimental design of experiments.....) by providing us with a scientific report from a student. What would be the best way or ways to study this without doing the experiment (I don't think I can!)? Are there some things I could study to assist me with those kinds of questions?
Don't worry about not being able to do the experiment. You will rarely actually get an experiment you've done before in class (VCAA definitely would not expect everybody to have done the exact prac), the main thing is trying to use the things you learnt from the experiments you did do to identify the strengths and weaknesses of whatever you see on your exam.

The experimental design part of chem is one of the more difficult ones and you will generally only be able to do the questions if you already have a very solid grasp of the theoretical content in 3/4 chem. Since you're in year 11 I think it's best to start with the theory and make sure you have those down pat before moving on to the experimental design.
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EllingtonFeint

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Re: VCE Chemistry Question Thread
« Reply #8165 on: October 14, 2019, 11:49:22 am »
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Hey,
I'm not too sure about how to tackle this question...
How exactly are you able to use the data booklet to tell which one of these fatty acids is an omega 3 one??
(I've attached pictures)

Thank you!
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hums_student

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Re: VCE Chemistry Question Thread
« Reply #8166 on: October 14, 2019, 12:28:00 pm »
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Hey,
I'm not too sure about how to tackle this question...
How exactly are you able to use the data booklet to tell which one of these fatty acids is an omega 3 one??
(I've attached pictures)

Thank you!

Remember an omega-3 fatty acid means that there is a double bond on the third carbon. From the information in the data booklet, you can try drawing out what its full structure would look like using the semi-structural formula given, and see which one would satisfy that.
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Re: VCE Chemistry Question Thread
« Reply #8167 on: October 14, 2019, 01:16:26 pm »
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Remember an omega-3 fatty acid means that there is a double bond on the third carbon. From the information in the data booklet, you can try drawing out what its full structure would look like using the semi-structural formula given, and see which one would satisfy that.

To clarify, it's the third carbon when reading the table from left to right, but in terms of naming conventions etc. it's the third last carbon.

You can simply look at the structural formula provided and see that arachidonic acid is omega 6, palmitoleic is omega 7, linolenic is omega 3, and linoleic acid is omega 6. 

jnlfs2010

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Re: VCE Chemistry Question Thread
« Reply #8168 on: October 14, 2019, 02:46:18 pm »
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Don't worry about not being able to do the experiment. You will rarely actually get an experiment you've done before in class (VCAA definitely would not expect everybody to have done the exact prac), the main thing is trying to use the things you learnt from the experiments you did do to identify the strengths and weaknesses of whatever you see on your exam.

The experimental design part of chem is one of the more difficult ones and you will generally only be able to do the questions if you already have a very solid grasp of the theoretical content in 3/4 chem. Since you're in year 11 I think it's best to start with the theory and make sure you have those down pat before moving on to the experimental design.

Any tips you could give me in doing this? How could I do this? Thanks :)
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angrybiscuit

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Re: VCE Chemistry Question Thread
« Reply #8169 on: October 14, 2019, 06:50:38 pm »
+6
Any tips you could give me in doing this? How could I do this? Thanks :)

Hello!
Doing as much experimental design question helps heaps ofc :) Also, VCAA also gives definitions of IV, DV and how to carry out an investigation, which is under 'Advice for Teachers' and 'Scientific Investigation.' https://www.vcaa.vic.edu.au/curriculum/vce/vce-study-designs/chemistry/advice-for-teachers/Pages/Index.aspx

VCAA will give you an experiment from potentially any of the course such as electrolysis, heat of combustion and even accuracy of equipment! (2019 NHT Exam). They will also make you evaluate things like a hypothetical battery or a hypothetical experimental setup. You need a really good grasp on what it means to be valid, reliable along with systematic and random errors.

Furthermore, you need a good grasp on the actual theory itself. For example, on the evaluation of the battery (which is also in 2019 NHT), you need to have strong knowledge on redox and secondary cells. I suggest to start doing exam style questions in order to get a really good grasp on the theoretical side of chemistry
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Re: VCE Chemistry Question Thread
« Reply #8170 on: October 15, 2019, 10:37:44 am »
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Hello!
Doing as much experimental design question helps heaps ofc :) Also, VCAA also gives definitions of IV, DV and how to carry out an investigation, which is under 'Advice for Teachers' and 'Scientific Investigation.' https://www.vcaa.vic.edu.au/curriculum/vce/vce-study-designs/chemistry/advice-for-teachers/Pages/Index.aspx

VCAA will give you an experiment from potentially any of the course such as electrolysis, heat of combustion and even accuracy of equipment! (2019 NHT Exam). They will also make you evaluate things like a hypothetical battery or a hypothetical experimental setup. You need a really good grasp on what it means to be valid, reliable along with systematic and random errors.

Furthermore, you need a good grasp on the actual theory itself. For example, on the evaluation of the battery (which is also in 2019 NHT), you need to have strong knowledge on redox and secondary cells. I suggest to start doing exam style questions in order to get a really good grasp on the theoretical side of chemistry

Thanks for the help!!! :)))
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EllingtonFeint

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Re: VCE Chemistry Question Thread
« Reply #8171 on: October 16, 2019, 11:51:54 am »
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Hey, so I have a few questions...

-How much are we expected to know about coal seam gas??
-How exactly are we able to tell how hygroscopic a molecule is? Is there a lot of this in the study design (cos I didn't see a bunch of it there)?
-Are there beta-amino acids as well as alpha-amino acids? And do beta ones just have the -NH2 and -COOH attached to different C atoms?

EDIT: are fuel cells and electrolytic cells the same thing?

Thanks! :)
« Last Edit: October 16, 2019, 05:57:00 pm by EllingtonFeint »
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Re: VCE Chemistry Question Thread
« Reply #8172 on: October 16, 2019, 03:39:20 pm »
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Hey guys!

For galvanic cells, does the mass loss of one electrode (anode) equal the mass gain of the other electrode (cathode)?

I assume no, but could someone explain why?
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angrybiscuit

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Re: VCE Chemistry Question Thread
« Reply #8173 on: October 16, 2019, 07:33:50 pm »
+4
Hey, so I have a few questions...

-How much are we expected to know about coal seam gas??
-How exactly are we able to tell how hygroscopic a molecule is? Is there a lot of this in the study design (cos I didn't see a bunch of it there)?
-Are there beta-amino acids as well as alpha-amino acids? And do beta ones just have the -NH2 and -COOH attached to different C atoms?

EDIT: are fuel cells and electrolytic cells the same thing?


1. Not much! Mainly the fact that it's non-renewable and its potential environmental threats (fracking can cause a lot of environmental damage in terms of leakages). Knowing what it's mostly composed of won't hurt either.
2. Hygroscopic molecules, put simply, are highly polar molecules (so much so that they tend to absorb moisture - water - from the air). Not much from the study design, you're right but it does come up a lot on the topics of biofuels. You need to know that biodiesels are more hygroscopic than petrodiesel, hence they'll have a higher water content which poses problems in terms of ignition.
3. Hm, not exactly my area of expertise. But from the study design and from the databook, you only need to know and focus on alpha-amino acids (or 2-amino acids). Unfortunately, I can't answer this question!
4. Fuel cells and electrolytic cells are most definitely NOT the same thing.
Fuel cells are just like galvanic cells but reactants are continuously supplied and hence can work indefinitely (as long as said reactants are supplied).
Electrolytic cells do not produce electricity unlike galvanic cells, they do the opposite. They convert electrical energy to chemical energy. Remember that in electrolytic cells, the polarities of the electrodes swap and the reaction will not proceed unless electrical energy is supplied (non-spontaneous).

Hope this helps!
 
somewhere, something incredible is waiting to be known.
carl sagan

angrybiscuit

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Re: VCE Chemistry Question Thread
« Reply #8174 on: October 16, 2019, 07:45:25 pm »
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Hey guys!

For galvanic cells, does the mass loss of one electrode (anode) equal the mass gain of the other electrode (cathode)?

I assume no, but could someone explain why?

You are correct, it does not equal UNLESS the species that are oxidised and reduced are the same thing. For example, take a copper electrolytic cell.
It has a copper anode and the cathode is the object to be plated and the electrolyte is a copper solution.

In this example let's say that 0.5 mole of copper is oxidised at the anode, it's safe to say that 0.5 mole of copper will be reduced at the cathode. Given that the molar masses are the same, the mass will be the same.

When the species differ, there are a number of things that makes the mass loss at the anode differ to the mass gained at the electrode.
One is the mole of electrons lost or gained by the species as stated by their respective half equations. Take for example a silver and copper battery.
Let's say that at the copper anode, 1 mole of copper is lost and two moles of electrons are 'formed.' Then at the silver half cell, two moles of silver is reduced as a result. From this example, the mass loss at the anode is not the same as the mass gained at the cathode which we can deduce solely from the mole ratios.

Another reason why is the molar mass of the species. In a zinc and copper battery, 1 mole of zinc is oxidised and 1 mole of copper is reduced. To find the respective masses, you would have to times them by their molar mass which is 65.4 g/mol and 63.5 g/mol respectively. So of course the mass lost at the respective electrodes would differ.

Hope this helps!

somewhere, something incredible is waiting to be known.
carl sagan