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March 28, 2024, 09:33:56 pm

Author Topic: VCE Chemistry Question Thread  (Read 2313038 times)  Share 

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cutiepie30

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Re: VCE Chemistry Question Thread
« Reply #9000 on: January 24, 2021, 07:33:41 pm »
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Hi Guys,

Could you please explain to me as to why Carbon-12 and Carbon-13 have the same amount of particles that is (6.02 x 10^23) when Carbon-13 has a greater mass than Carbon-12?

It is briefly explained in the attached document, but I don't exactly get as to why 12 grams was chosen to analyse the number of particles in a mole

Thanks so much :)

Erutepa

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Re: VCE Chemistry Question Thread
« Reply #9001 on: January 24, 2021, 08:01:26 pm »
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Hi Guys,

Could you please explain to me as to why Carbon-12 and Carbon-13 have the same amount of particles that is (6.02 x 10^23) when Carbon-13 has a greater mass than Carbon-12?

It is briefly explained in the attached document, but I don't exactly get as to why 12 grams was chosen to analyse the number of particles in a mole

Thanks so much :)
I think what this attached documents is saying is that the mole is defined as the amount of carbon-12 atoms in 12g of carbon 12. The document is saying that 12g of carbon 12 was chosen as 12g is the same number as its mas number and isotopic mass (basically 12 was a nice number to pick).
Since there are aprox. 6.02X10^23 atoms in 12g of carbon-12, this is the definition of the mole. That is to say, 1 mole of a element is 6.02X10^23 atoms.
For carbon-13, each atom has a greater mass due to the additional neutron, as such one mole of carbon-13 (which is the same number of atoms as 1 mole of carbon-12) will have a greater mass. If this is confusing, it can help to substitute the concept of a mole with the concept of a dozen. A dozen 10g balls will have a greater collective mass than a dozen 9g balls. Here a mole is essentially functioning the same a 'a dozen' it is simply a particular number of things. Where a dozen is 12 things - a mole is 6.02X10^23 things.

As an interesting side note, this is no longer how the mole is defined! You do not need to know this however for VCE chem :)
« Last Edit: January 24, 2021, 08:58:35 pm by Erutepa »
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cutiepie30

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Re: VCE Chemistry Question Thread
« Reply #9002 on: January 24, 2021, 09:16:14 pm »
+1
I think what this attached documents is saying is that the mole is defined as the amount of carbon-12 atoms in 12g of carbon 12. The document is saying that 12g of carbon 12 was chosen as 12g is the same number as its mas number and isotopic mass (basically 12 was a nice number to pick).
Since there are aprox. 6.02X10^23 atoms in 12g of carbon-12, this is the definition of the mole. That is to say, 1 mole of a element is 6.02X10^23 atoms.
For carbon-13, each atom has a greater mass due to the additional neutron, as such one mole of carbon-13 (which is the same number of atoms as 1 mole of carbon-12) will have a greater mass. If this is confusing, it can help to substitute the concept of a mole with the concept of a dozen. A dozen 10g balls will have a greater collective mass than a dozen 9g balls. Here a mole is essentially functioning the same a 'a dozen' it is simply a particular number of things. Where a dozen is 12 things - a mole is 6.02X10^23 things.

As an interesting side note, this is no longer how the mole is defined! You do not need to know this however for VCE chem :)

Thanks So Much, its makes so much sense now :)

thenuttyprofessor

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Re: VCE Chemistry Question Thread
« Reply #9003 on: January 25, 2021, 11:40:50 am »
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Hey,

I'm looking to do old SD Unit 3 Exams. Just wanted to know what content would be relevant/irrelevant to the current SD, and whether if some topics from the old Unit 3 appear in the current Unit 4 (which I have not covered)

Thanks.

Jinju-san

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Re: VCE Chemistry Question Thread
« Reply #9004 on: January 26, 2021, 03:05:55 pm »
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Hey everyone!

How would you answer this question? (question 4 e).
The only possible limitation that I can think of is that your calculations would not be entirely accurate, because some of the heat would inevitably be lost to the surroundings or end up simply heating the gauze mat or beaker instead of solely heating the water…

Is there any thing else I could possibly add to this?

This is the photo:
https://drive.google.com/file/d/1qJOGN2WLrZsCHyGbo8ZLxUB8tPvG5NDa/view?usp=sharing
Thank you!

Willtonytomcas

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Re: VCE Chemistry Question Thread
« Reply #9005 on: January 26, 2021, 03:14:32 pm »
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Hey everyone!

How would you answer this question? (question 4 e).
The only possible limitation that I can think of is that your calculations would not be entirely accurate, because some of the heat would inevitably be lost to the surroundings or end up simply heating the gauze mat or beaker instead of solely heating the water…

Is there any thing else I could possibly add to this?

This is the photo:
https://drive.google.com/file/d/1qJOGN2WLrZsCHyGbo8ZLxUB8tPvG5NDa/view?usp=sharing
Thank you!

The question asks to explain the limitations of the method.
As seen in the apparatus set up, not all of the heat from the bunsen burner is being transferred to the water as there is a significant gap between the flame and the beaker which will lead to some heat being transferred to the surroundings, thus the not all of the energy from the fuel is transferred to the water.

I hope that helps - it is not a direct answer to the question but it should give you the jist of what to think about :)
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jasmine24

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Re: VCE Chemistry Question Thread
« Reply #9006 on: January 27, 2021, 08:50:02 am »
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Would anyone be able to explain multiple choice Q17 on the 2018 VCAA chemistry exam? Im not sure why the ratio 5/2 is used when calculating n(H2C2O4)
thanks!

Jinju-san

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Re: VCE Chemistry Question Thread
« Reply #9007 on: January 27, 2021, 09:44:23 am »
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Would anyone be able to explain multiple choice Q17 on the 2018 VCAA chemistry exam? Im not sure why the ratio 5/2 is used when calculating n(H2C2O4)
thanks!

Hi jasmine24!
So for this question, the balanced equation for the titration tells us that the ratio of H2C2O4 to KMnO4 is 5:2. This means that for every 2 moles of potassium permanganate that is present, 5 moles of oxalic acid will react with it. Therefore, you need to multiply the number of moles of KMnO4 by 5/2 to obtain the number of moles of H2C2O4 that reacted.

Hope this helps!
« Last Edit: January 27, 2021, 09:46:51 am by Jinju-san »

Chocolatepistachio

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Re: VCE Chemistry Question Thread
« Reply #9008 on: January 31, 2021, 04:51:51 pm »
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can someone explain what is happening here how is this molecule produced how do you know that you need 2 of that ring molecule

and for this what does the dash next to the r mean the one dash and the two dashes

WhatisaMeMe

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Re: VCE Chemistry Question Thread
« Reply #9009 on: January 31, 2021, 04:56:25 pm »
+1
Hi, do we need to memorise exact energy contents of fuels like for coal it is 32kj/g? or do we just need to know if one energy content is higher than another when comparing fuels?

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tiredandstressed

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Re: VCE Chemistry Question Thread
« Reply #9010 on: January 31, 2021, 07:35:41 pm »
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and for this what does the dash next to the r mean the one dash and the two dashes
The R is a variable group; since you know an amide has a CONH bond you were required to draw that. 'R' just shows that any group can attach to the atom (so it is basically any group)
Different dashes might mean that they are different group (for example for a scalene triangle, you would mark each side with a different number of strokes, to show they aren't the same) that is what i believe is happening but i am not 100% sure
« Last Edit: January 31, 2021, 07:37:14 pm by tiredandstressed »
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miyukiaura

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Re: VCE Chemistry Question Thread
« Reply #9011 on: February 03, 2021, 04:50:26 pm »
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Why is the energy content of (bio)ethanol so low? Does it have something to do with the hydroxyl groups being able to bond with water?
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Chocolatepistachio

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Re: VCE Chemistry Question Thread
« Reply #9012 on: February 03, 2021, 05:21:41 pm »
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If someone could help me with this question

SmartWorker

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Re: VCE Chemistry Question Thread
« Reply #9013 on: February 05, 2021, 07:22:30 pm »
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Hi,

For this question: for part b, why is the reducing agent SO2 and not the S4+ in SO2 and likewise for parts c and d when i checked the answers, they had the compound instead of the ions?


Thank you!
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keltingmeith

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Re: VCE Chemistry Question Thread
« Reply #9014 on: February 06, 2021, 06:10:55 pm »
+10
Why is the energy content of (bio)ethanol so low? Does it have something to do with the hydroxyl groups being able to bond with water?

Pure bioethanol is exactly the same as pure ethanol - doesn't matter how that chemical was made, a chemical is a chemical. However, due to the way bioethanol is produced, it is normally contaminated with other products, thus reducing the amount of energy per gram - it's just that there's less ethanol in each portion in the first place.

If someone could help me with this question

Change in enthalpy/entropy = products - reactants (EDIT: had this the wrong way before - it's fixed now)

Hi,

For this question: for part b, why is the reducing agent SO2 and not the S4+ in SO2 and likewise for parts c and d when i checked the answers, they had the compound instead of the ions?
(Image removed from quote.)

Thank you!

Firstly - you are correct in identifying that S is oxidised from +4 to +6. However, S is not the chemical that caused the O2 to be reduced from 0 to -2. Reducing and oxidising agents must be a chemical that causes a change - it doesn't matter which part of the chemical underwent the change, the whole chemical is the agent. Hence, SO2 is the reducing agent, even though it's the sulfur specifically that changed its oxidation state and was oxidised.