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July 09, 2020, 11:55:09 am

Author Topic: VCE Chemistry Question Thread  (Read 1210131 times)  Share 

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keltingmeith

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Re: VCE Chemistry Question Thread
« Reply #8625 on: June 06, 2020, 07:24:56 pm »
+6
Thanks!

Would it be correct if I said for the definition of chiral centre

An atom that has four different groups bonded to it and the structures are mirror images of each other eg tartaric acid

The structures don't have to have mirror images, because it doesn't make sense with chiral centres. If a molecule has two chiral centres, you have 4 different stereoisomers: (R,R), (R,S), (S,R), and (S,S). Let's say you have the (R,S) molecule - its mirror image (or its enantiomer, see below for that correction) is (S,R). But in this case, there's two whole stereoisomers you've forgotten about - (R,R) and (S,S). This is actually true for the example you've given - tartaric acid has two chiral centres. I'd instead just stop at a chiral centre being a centre with four different groups attached to it (for interest: this doesn't even need to be a carbon molecule, out could be a nitrogen for example, but I feel that's beyond the scope of VCE. It's not even that complicated, but if the idea confuses you, just ignore it)

And for the definition of enantiomer - chiral molecules that are mirror images of one another . The molecules cannot be placed on top of one another and give the same molecule eg d- alanine and l-alanine

By "mirror images of each other", I'm assuming you mean the two molecules of differing chirality, not the molecule with itself? In which case, enantiomers definition is spot on in the first sentence only. The second sentence is a bit wrong in that you claim they're "the same molecule". If they were the same molecule, they'd have the same chirality. Some textbooks make it sound like molecules of differing chirality are the same, but they're not, or they wouldn't have different names. They can have the same functional groups, behave the same way in an achiral environment, and have the same connectivity - but their spatial arrangement is entirely different. Stick with just the first sentence, that's a perfect definition

If my definition of micelle was
A cluster of molecules that are found in certain solutions. A micelle forms due to the amphiphatic nature of fatty acids.
Would it be correct

You're half correct - you would HAVE to mention that the cluster is spherical formed with the lipophilic part of the molecule pointing onwards, and the hydrophilic part pointed towards to make a sphere. There are lots of supramolecular structures that your definition fits, including lipid bilayers, liposomes, vesicles, etc. I'm not sure how much of this is in the scope of VCE, BUT I couldn't find mention of even micelles in the study design, so this question may be redundant. All I know is that I, personally, would not accept that definition unless you at least also mentioned the shape of the cluster, because a cluster could be anything
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Annasimon

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Re: VCE Chemistry Question Thread
« Reply #8626 on: June 06, 2020, 09:02:08 pm »
0
For this question:
What kind of tests would need to be done to make sure that cyclotides either naturally or genetically have no harmful effects on humans or other organims

Could I say
- they have to be tested in clinical trials on humans
- they would have to be tested using human cells grown in the laboratory

Also what are some of the ways scientists are trying to combat malaria and how effective will these be

Thanks!

jammol7

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Re: VCE Chemistry Question Thread
« Reply #8627 on: June 07, 2020, 08:33:53 pm »
+3
For this question:
What kind of tests would need to be done to make sure that cyclotides either naturally or genetically have no harmful effects on humans or other organims

Could I say
- they have to be tested in clinical trials on humans
- they would have to be tested using human cells grown in the laboratory

Also what are some of the ways scientists are trying to combat malaria and how effective will these be

Thanks!

Sorry I can't help but, is this on the study design? I literally do not remember doing this at school.
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thatdumbstudent

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Re: VCE Chemistry Question Thread
« Reply #8628 on: June 08, 2020, 05:49:02 pm »
0

can someone help me use collision theory to explain electrolysis rate?
so I was wondering how to explain the rate in terms of electrolysis. So we were investigating how surface area of electrodes affects rate of electrolysis of copper sulphate with copper electrodes.

so i'd say as the s.a. increases, the number of successful collisions increases which means the proportion of successful collisions per unit time increases.

but i feel like i should mention copper ions somewhere in that sentence and idk how to incorporate it if that makes any sense? thanks!

keltingmeith

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Re: VCE Chemistry Question Thread
« Reply #8629 on: June 09, 2020, 07:30:39 pm »
+3
can someone help me use collision theory to explain electrolysis rate?
so I was wondering how to explain the rate in terms of electrolysis. So we were investigating how surface area of electrodes affects rate of electrolysis of copper sulphate with copper electrodes.

so i'd say as the s.a. increases, the number of successful collisions increases which means the proportion of successful collisions per unit time increases.

but i feel like i should mention copper ions somewhere in that sentence and idk how to incorporate it if that makes any sense? thanks!

Well, where would you include the copper ions? What are the copper ions doing? Have you already mentioned the copper ions without realising it? (Hint: even if the equation is Cu2+ + 2e- -> Cu, the electrons aren't free-flowing, they have to come from somewhere)
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Chocolatepistachio

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Re: VCE Chemistry Question Thread
« Reply #8630 on: June 10, 2020, 09:11:23 pm »
0
Why is ethanol both polar and non polar

Why would cellulose be considered a renewable resource

An organic liquid when reacted with concentrated Sulfuric acid produces a compound that immediately decolourises bromine water
What is the formula of the organic liquid
A c5H10
B C5H 12
C C5H11OH
D C5H11O

Why is the answer for this c

Do polymerisation and condensation reactions both produce water molecule
 

wsdm

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Re: VCE Chemistry Question Thread
« Reply #8631 on: June 10, 2020, 10:07:24 pm »
+7
Why is ethanol both polar and non polar
Ethanol is actually a polar molecule. The reason that it is sometimes referred to as polar and non-polar is due to its non-polar \(C_2H_5\) group and polar due to its \(OH\) group. The former group enables ethanol to be soluble in non polar solvents and the latter group enables ethanol to be soluble in polar solvents, however, since it can be dissolved in water, it would be considered a polar molecule.

Why would cellulose be considered a renewable resource
The fact that cellulose is obtained from organic matter, i.e. plants in this case, makes it a renewable energy source. Cellulose can be replenished within our lifetime and can be reformed (unlike fossil fuels, which take millions of years to form).

An organic liquid when reacted with concentrated Sulfuric acid produces a compound that immediately decolourises bromine water
What is the formula of the organic liquid
A c5H10
B C5H 12
C C5H11OH
D C5H11O

Why is the answer for this c
In the case of option C, pentanol is being dehydrated by the sulfuric acid. The sulfuric acid acts as an acidic catalyst to "remove" water from the alcohol, so to speak. When pentanol is dehydrated, it forms pentene and water. Therefore, pentene can then react with bromine water to decolourise it by breaking the double bond and then forming bromopentane (due to an addition reaction).

Do polymerisation and condensation reactions both produce water molecule
 
Both polymerisation and condensation are addition reactions. Polymerisation refers to the joining of monomers to produce a single polymer, whilst condensation refers to adding two molecules to produce an addition product and a water molecule. In the case of addition polymerisation, water molecules aren't produced, but in condensation polymerisation, it produces water molecules, as in the example of polyamides.
« Last Edit: June 10, 2020, 10:10:12 pm by wsdm »
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Chocolatepistachio

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Re: VCE Chemistry Question Thread
« Reply #8632 on: June 11, 2020, 11:58:26 am »
0
If something has an OH group then it will always be polar?

Why do polysaccharides provide the lowest amount of energy per gram for the human body compared to amino acids, triglyceride and monosaccharide.

Would chloroform be considered an alkyl halide

Apart from being used in metabolism what else are NAD and FAD used for in living systems

What are the differences between the structure of quinine and chloroquinine

Thanks!

« Last Edit: June 11, 2020, 12:03:13 pm by Chocolatepistachio »

keltingmeith

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Re: VCE Chemistry Question Thread
« Reply #8633 on: June 11, 2020, 12:36:20 pm »
+2
Only answering a couple:

If something has an OH group then it will always be polar?

Would chloroform be considered an alkyl halide

What are the differences between the structure of quinine and chloroquinine

Consider the molecule C(OH)4 - it will not be polar. So no, you can't assume an OH group means polar. You should learn to quickly draw polarity arrows in your head to determine if it's polar or not.

Yes, chloroform is an alkyl halide.

There are LOTS of differences, but for a start, one has chlorine in it, the other does not. What's the context behind the question?
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Chocolatepistachio

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Re: VCE Chemistry Question Thread
« Reply #8634 on: June 11, 2020, 01:01:51 pm »
0
For that questions it says looking at the structures what parts of the molecule are the same and which parts are different

Could I say chloroquinine has a chloro side group whereas quinine has an OH bond and an O bond

keltingmeith

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Re: VCE Chemistry Question Thread
« Reply #8635 on: June 11, 2020, 09:14:03 pm »
+2
Could I say chloroquinine has a chloro side group whereas quinine has an OH bond and an O bond

I mean, that's not very specific, but also this question is a weird one and those two molecules are different enough you could spend paragraphs describing the differences. I think you're better off asking your teacher for advice here - is this something they'd expect you to answer in an exam? Or is this just them testing your knowledge? How many differences would they expect you to pick up? (Because there are more differences than similarities here - it's like asking what's the difference between the songs Radioactive and Shape of You. The chords might be the same, but that's about it)
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Chocolatepistachio

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Re: VCE Chemistry Question Thread
« Reply #8636 on: June 12, 2020, 12:33:00 am »
0
Ok. Thanks

For the phenol molecule how much is used annually

I couldn’t find how much is used only how much is produced

For this question
What is the purpose of using concentrated sulfuric acid in esterification reactions
A to dehydrate the system
B To catalyse the reaction
C  to be a reactant
D to hydrate the system

Why is it b

ErnieTheBirdi

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Re: VCE Chemistry Question Thread
« Reply #8637 on: June 12, 2020, 10:03:31 am »
0
Hey everyone, I just wanted to ask you all something and maybe for some advice. I’ve just had two SACs for Unit 1 Chem. I ended up getting a 68 and a 45... I don’t understand why though, like I did all the practice and everything, and it isn’t the “exam stress/nervousness” I do it the exact same way I do the practice but it’s still wrong. My teacher’s advice was that “you chose the hardest subject in this school, and it’s only going to get harder, I cannot do more to help other than teach it well, and I do.” What do I do? I do like the subject and I do study and everything but I do it right in the practice but completely wrong in the Tests/ exams? I still have an exam left this semester. What do I do? Should I...drop or persist and keep going ? Any advice on how to fix this problem or what I should do going forward ?

keltingmeith

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Re: VCE Chemistry Question Thread
« Reply #8638 on: June 12, 2020, 10:33:00 am »
+5
Hey everyone, I just wanted to ask you all something and maybe for some advice. I’ve just had two SACs for Unit 1 Chem. I ended up getting a 68 and a 45... I don’t understand why though, like I did all the practice and everything, and it isn’t the “exam stress/nervousness” I do it the exact same way I do the practice but it’s still wrong. My teacher’s advice was that “you chose the hardest subject in this school, and it’s only going to get harder, I cannot do more to help other than teach it well, and I do.” What do I do? I do like the subject and I do study and everything but I do it right in the practice but completely wrong in the Tests/ exams? I still have an exam left this semester. What do I do? Should I...drop or persist and keep going ? Any advice on how to fix this problem or what I should do going forward ?

One of my favourite teachers used to always say to us, "practice doesn't perfect - perfect practice makes perfect". Now, he said this in regards to singing, but I feel it holds just as true with typical study.

You can't just do the practice questions and expect to do well. That's just practice, and all it will do is teach you how to answer those specific questions. So, perfect practice would be doing every single possible question ever? Of course not, you'd be sitting at your desk forever.

IMHO (and I encourage everyone reading this to comment as well, and say what works for you, or what you think "perfect practice" looks like), "perfect practice" is all about thinking about things physically and drawing an understanding of them. If a question asks you, "I mixed 50L of ethanol with 20L of ethanoic acid, how much ethyl ethanoate will I get?" - don't just start chugging through maths. Draw up the reaction scheme, make sure you know how ethyl ethanoate is even being made. Which part is the ethanol, and which part is the acid? What are the by-products, how are they forming? Next, what equations do you need? Can you combine them to make the calculation in one step? Is it beneficial to do it that way? Why those equations, why not other equations?

Don't just answer the question in front of you, try to answer every question that could be asked. And never start by just plugging numbers in - draw everything out. Something that I think gets lost on students a lot is that chemistry is a physical science. It's tangible, you can touch it with your own hands, and actually do this experiments. So those questions describing experiments ABSOLUTELY should be able to be drawn and understood, both on a macroscopic level (i.e., as if you were doing it), but also on the atomic level.

My understanding of chemistry fundamentally changed in university when I was forced to draw out what was happening on an atomic level. It never even mattered if I was right or wrong - by being forced to do it, I started thinking deeper, and my grades improved as a natural consequence.

So yeah, a lot there, but recommendations:
-Draw everything. Draw the atoms, draw the molecules, draw the cauldron bubbling - if you think it's relevant, draw it
-Try to understand everything as deeply as possible
-And of course, only take this advice when studying. If it helps you answer the question, draw it - but you also want to save time in an exam, so try to either draw quick, or learn to draw in your head

Ok. Thanks

For the phenol molecule how much is used annually

I couldn’t find how much is used only how much is produced

For this question
What is the purpose of using concentrated sulfuric acid in esterification reactions
A to dehydrate the system
B To catalyse the reaction
C  to be a reactant
D to hydrate the system

Why is it b

For the phenol, I got nfi, sorry man. For the sulfuric acid, the answer is honestly just - because it is. You might want to go over your esterification notes some more.
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colline

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Re: VCE Chemistry Question Thread
« Reply #8639 on: June 12, 2020, 10:42:06 am »
+5
Don't just answer the question in front of you, try to answer every question that could be asked. And never start by just plugging numbers in - draw everything out. Something that I think gets lost on students a lot is that chemistry is a physical science. It's tangible, you can touch it with your own hands, and actually do this experiments. So those questions describing experiments ABSOLUTELY should be able to be drawn and understood, both on a macroscopic level (i.e., as if you were doing it), but also on the atomic level.

This is so true! My approach to chem was very much “mmmkay so this is the formula we learnt in class and here are the numbers so let’s just chuck everything into an equation and hope for the best”. It worked well for me in maths but chem is definitely different.

My chem teacher once said that the difference between a low 40 and mid/high 40 in chem is that the former KNOWS the content, but the latter UNDERSTANDS it.

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