VCE Chemistry Question Thread

[VanillaRice]

Can someone explain the difference between carbon and hydrogen environments?
Also, what's the easiest way to find the number of carbon and hydrogen environments?

Thanks!

Technically speaking, carbon environments are carbon atoms that produce the same peak on a C-13 NMR spectrum, while hydrogen environments are hydrogen atoms that produce the same peak on a H-1 NMR spectrum.
In other words, each carbon atom is an environment. However, equivalent carbon environments are carbon environments that are just that - exactly the same. They have the same connectivities to surrounding atoms. The principle applies to hydrogen environments.

In my opinion, the easiest way to find such environments is to find planes of symmetry in the molecule - that way, you're only worrying about one half of the molecule (since the other half is the same i.e. will have corresponding equivalent environments on the other half). From there, circle all of your carbons or hydrogens (generally, it's safe to consider hydrogens bonded to the same carbon to be equivalent). Then, see which ones have the same surrounding atoms. Now, you can count all of your unique environments

Hope this helps

[Phenomenol]

Hello! Doesn't that mean iron is reduced, and cadmium is oxidase and not the other way around? Also, I still don't really understand why we use, for example the value 0.62V for the Fe3+/Fe2+ only half cell if the 0.62 value was obtained from a cell that used Fe3+/Fe2+ and Sn4+/Sn2+? Confused af hahaha

Firstly, notice in the galvanic cell on the left that the polarity of the Sn electrode is reversed compared to in the galvanic cell on the right. That means on the left, Sn⁴⁺ is undergoing reduction but on the right Sn²⁺ is undergoing oxidation. You should then deduce Fe³⁺ is a stronger oxidant than Cd²⁺ because Fe³⁺ is able to oxidise Sn²⁺ but Cd²⁺ is not able to oxidise Sn²⁺, NOT because of the difference in magnitude of the EMF values. The signs on the electrodes mean EVERYTHING.

You then know under standard conditions the Fe³⁺/Fe²⁺ reduction potential is 0.62 V above that of Sn⁴⁺/Sn²⁺, which is in turn 0.55 V above that of Cd²⁺/Cd. This is why constructing a galvanic cell between the two extreme half-cells gives you the sum of the differences between the potentials as the EMF.

In the galvanic cell on the right, the Fe³⁺ being the oxidant is itself reduced at the cathode and the Sn²⁺ being the reductant is itself oxidised at the anode.

Hope that clears up confusion.

[tinagranger]

Hi guys, For this part of the study design:
Comparison of glucose, fructose, sucrose and the artificial sweetener aspartame with reference to their structures and energy content

I don't get what information we need to know. I can't find anything specific on this in the textbook - could someone summarise all the info we need to know for this/?

[Bri MT]

Can someone explain the difference between carbon and hydrogen environments?
Also, what's the easiest way to find the number of carbon and hydrogen environments?

Thanks!

When you look at carbon environments you ask "What atoms is this carbon connected to?".
For example, in propan-1-ol there are three carbon environments.
-1 is attached to 3Hs and 1C
-Another is attached to 2Cs and 2Hs
-Finally, the last one is is bonded to 1O, 2Hs, and 1C

In propane, there are two carbon environments
-1 is attached to 2Cs and 2Hs
-2 are attached to 3 Hs and 1C

Some people get confused with this when you have butan-1-ol
-1 is attached to 3Hs and 1C
-1 is attached to 2Cs and 2 Hs
-1 is attached to 1C, 1 slightly positive C and 2Hs
-1 is attached to 1C, 2Hs, and 1O
Lots of students will think that there are 3 hydrogen environments, but atoms behave differently depending on what they are attached to, so the two CH2 environments are actually different, because the carbons they are connected to will act differently.

Hope this helps

[VanillaRice]

Hi guys, For this part of the study design:
Comparison of glucose, fructose, sucrose and the artificial sweetener aspartame with reference to their structures and energy content

I don't get what information we need to know. I can't find anything specific on this in the textbook - could someone summarise all the info we need to know for this/?

I'd assume you'd be expected to know how to distinguish the differences between their structures. What are the similarities between glucose and fructose? What makes them different/similar to sucrose? How are glucose, fructose and sucrose different to aspartame? Note the structures of all these molecules are in your data book.

I'm not sure what textbook you're using, but I think there should at least be a section that discusses the sweetness of carbs. Why is aspartame used over sucrose? Think about this in terms of their energy content and sweetness.

Hope this helps

[Wordswurth]

Hi guys, For this part of the study design:
Comparison of glucose, fructose, sucrose and the artificial sweetener aspartame with reference to their structures and energy content

I don't get what information we need to know. I can't find anything specific on this in the textbook - could someone summarise all the info we need to know for this/?

Basically, artificial sweeteners have the same energy content as glucose with the exception that you use smaller quantities of artificial sweeteners like aspartame because they're really sweet compared to glucose and other sugars.

As for the structures and energy content of the sugars, you can find them in the data book, I think. I don't have it with me currently but I'm pretty certain they're in there somewhere! Feel free to correct me where I'm wrong and ask questions if there is something unclear about what I said

[Somedudelmaoy]

Are past vcaa exams still semi-relevant?

[Sine]

Are past vcaa exams still semi-relevant?

yes definitely a lot of the past vcaa questions are still relevant and could come up this year.

[Syedali_]

When answering numerical questions, when should it be in scientific form? can it be the other form without losing marks?

[Bri MT]

When answering numerical questions, when should it be in scientific form? can it be the other form without losing marks?

Use your judgement here. I don't think there is a set rule, but if there's more than 3 trailing or leading zeros I think it's a good idea. Similarly, if you have less significant figures than the amount of of place values, I'd consider converting.


You are expected to know how to convert, so if it was obvious eg 120000000 kJ I suspect they might

[Gogo14]

U know how oxidatipn is the gain of oxygen  and loss of hydrogen, and reduction is the loss of oxygen and gainof hydrogen
What happens if a compound gains both hydrogen and oxygen? Is it oxidation, reduction, both or neither (if you cannot determin the oxidation numbers)

[rainbowsparkles15]

Hey guys,
Does anyone have a list of exam questions that are relevant to the current study design?

[sweetiepi]

When answering numerical questions, when should it be in scientific form? can it be the other form without losing marks?

Use your judgement here. I don't think there is a set rule, but if there's more than 3 trailing or leading zeros I think it's a good idea. Similarly, if you have less significant figures than the amount of of place values, I'd consider converting.


You are expected to know how to convert, so if it was obvious eg 120000000 kJ I suspect they might

I'd definitely say for three or more trailing/leading zeros, I would put it into scientific notation. This is also general convention in (most) uni chem units, so it is best to get into the habit of converting between the two early

EDIT: typo

[sweetcheeks]

U know how oxidatipn is the gain of oxygen  and loss of hydrogen, and reduction is the loss of oxygen and gainof hydrogen
What happens if a compound gains both hydrogen and oxygen? Is it oxidation, reduction, both or neither (if you cannot determin the oxidation numbers)

It depends. If it gains 2 hydrogen and 1 oxygen, it will be neither (2 x +1 for hydrogens and 1 x -2 for oxygen will cancel out). If it gains one hydrogen and one oxygen, it will be oxidation. If it gains 3 hydrogens and 1 oxygen, it will be reduction.

[sweetiepi]

Hey guys,
Does anyone have a list of exam questions that are relevant to the current study design?

Hey there!
I don't have a list of exam questions relevant to the current study design, however as Sine said a few posts back:

yes definitely a lot of the past vcaa questions are still relevant and could come up this year.

Therefore, I'd recommend looking at some of the questions in the 2013-2016 papers.