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March 29, 2024, 11:11:25 pm

Author Topic: VCE Chemistry Question Thread  (Read 2313792 times)  Share 

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Rose34

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Re: VCE Chemistry Question Thread
« Reply #9240 on: January 08, 2022, 08:25:41 pm »
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Another question, in my book it says that the electron charge is -1.60*10^19C but when this concept is applied they changed the electron charge to 1.60*10^-19C(thus getting a +ve value), BUT when I checked the chem data book, the electron charge is noted to be -1.60*10^-19C, so now I am confused of which one to use? obviously, I would rely on the value in the data book right? but why are the charges so different?

Thanks in advance!

ArtyDreams

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Re: VCE Chemistry Question Thread
« Reply #9241 on: January 08, 2022, 09:39:56 pm »
+5
Can someone explain why the anode is positive and the cathode is negative in electrolytic cells?

Thanks in advance!

In any electrical circuit, the electrons flow from the positive to the negative terminal (direction of conventional current).
We also know that in any cell, whether galvanic or electrolytic, electrons flow from the anode, to the cathode.
To satisfy both of these facts, the anode must be positive, and the cathode negative, so electrons can flow from the anode to cathode. Don't forget that the anode is connected to the positive side of the battery, while cathode is connected to the negative side.

Galvanic cells don't require a battery, so the polarities are the opposite (electrons flow from anode to cathode, where anode is negative and cathode is positive).

I've attached two images below which should hopefully explain what I said a bit better.

Another question, in my book it says that the electron charge is -1.60*10^19C but when this concept is applied they changed the electron charge to 1.60*10^-19C(thus getting a +ve value), BUT when I checked the chem data book, the electron charge is noted to be -1.60*10^-19C, so now I am confused of which one to use? obviously, I would rely on the value in the data book right? but why are the charges so different?

Thanks in advance!

I'm not really sure where that first value comes from, so I won't answer for that but 1.60*10^-19 is the charge of an electron (and the value in the Physics data sheet.). The -1.60*10^-19 value just notes that the charge of an electron is negative. Using 1.60*10^-19 is accurate and you can use this, but just make sure to keep in mind that the charge of the electron is negative.

Hope this helps, let me know if you have any other questions :)



« Last Edit: January 08, 2022, 09:47:12 pm by ArtyDreams »

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Re: VCE Chemistry Question Thread
« Reply #9242 on: January 09, 2022, 08:45:28 am »
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Why does the concentration of solutes dissolved in a reaction influence the rate of reaction? I was wondering if it has anything to do with how often the particles will collide with each other, but I'm not exactly sure if this train of thought is right..

Can someone please verify if this is correct and if not, what's the actual reason?

Thank you!

ArtyDreams

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Re: VCE Chemistry Question Thread
« Reply #9243 on: January 09, 2022, 11:02:05 am »
+5
Why does the concentration of solutes dissolved in a reaction influence the rate of reaction? I was wondering if it has anything to do with how often the particles will collide with each other, but I'm not exactly sure if this train of thought is right..

Can someone please verify if this is correct and if not, what's the actual reason?

Thank you!

Hi - yes you are correct!

The higher the concentration of a substance, the more solute of it there is is dissolved in a solvent. Think about it in terms of salt water. You take two cups of water each with 100 ml of water in it. You then put two tablespoons of salt in the first cup, and 5 tablespoons of salt in the second cup. Which has the highest concentration? It's the second one, as you've put more salt particles (i.e NaCl) in the same amount of volume. Therefore, there is a higher chance of the NaCl molecules colliding with each other, as theres more particles in the same amount of space.

The greater the concentration, the more likely that collisions between molecules will occur. This will lead into a higher amount of successful collisions, which can increase the rate of the reaction.

Hope this helps :)

EDIT - you can also think about it in terms of two rooms. Lets say there are two rooms, that are the exact same size. One room has 5 people, and the other room has 20 people. Say you walked into each of the rooms. Which room would have a greater chance of you walking into other people?
« Last Edit: January 09, 2022, 11:04:20 am by ArtyDreams »

Rose34

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Re: VCE Chemistry Question Thread
« Reply #9244 on: January 09, 2022, 09:33:06 pm »
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In any electrical circuit, the electrons flow from the positive to the negative terminal (direction of conventional current).
We also know that in any cell, whether galvanic or electrolytic, electrons flow from the anode, to the cathode.
To satisfy both of these facts, the anode must be positive, and the cathode negative, so electrons can flow from the anode to cathode. Don't forget that the anode is connected to the positive side of the battery, while cathode is connected to the negative side.

Galvanic cells don't require a battery, so the polarities are the opposite (electrons flow from anode to cathode, where anode is negative and cathode is positive).

I've attached two images below which should hopefully explain what I said a bit better.

I'm not really sure where that first value comes from, so I won't answer for that but 1.60*10^-19 is the charge of an electron (and the value in the Physics data sheet.). The -1.60*10^-19 value just notes that the charge of an electron is negative. Using 1.60*10^-19 is accurate and you can use this, but just make sure to keep in mind that the charge of the electron is negative.

Hope this helps, let me know if you have any other questions :)

Makes sense thank you!

Rose34

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Re: VCE Chemistry Question Thread
« Reply #9245 on: January 12, 2022, 02:30:17 pm »
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Can someone clarify what an alkyl group is? from my understanding when you remove a hydrogen from the ammonia(NH3) it becomes NH2 and so NH2 is the alkyl group?
Also, is the alkyl group the same as primary amine (when you have NH2)? So NH2=alkyl group=primary amine?

Thanks in advance.

Billuminati

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Re: VCE Chemistry Question Thread
« Reply #9246 on: January 12, 2022, 02:33:39 pm »
+1
Can someone clarify what an alkyl group is? from my understanding when you remove a hydrogen from the ammonia(NH3) it becomes NH2 and so NH2 is the alkyl group?
Also, is the alkyl group the same as primary amine (when you have NH2)? So NH2=alkyl group=primary amine?

Thanks in advance.

Alkyls are actually alkanes with 1 H removed at the end
VCE 2016-2018

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Rose34

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Re: VCE Chemistry Question Thread
« Reply #9247 on: January 12, 2022, 11:47:46 pm »
0
Alkyls are actually alkanes with 1 H removed at the end

oh ok, thank you!

Rose34

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Re: VCE Chemistry Question Thread
« Reply #9248 on: January 24, 2022, 07:34:27 am »
0
Hello,

I have a questions regarding principles of NMR, can you change the spin statr from high to low? also, does the presence of electrons around the nucleus makes it hsrder to change the spin state?

Thanks in advance,
Rose. 

Billuminati

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Re: VCE Chemistry Question Thread
« Reply #9249 on: January 24, 2022, 09:04:56 am »
+3
Hello,

I have a questions regarding principles of NMR, can you change the spin statr from high to low? also, does the presence of electrons around the nucleus makes it hsrder to change the spin state?

Thanks in advance,
Rose.

There must be a return from high energy to low energy spin state since everything in chem is about achieving the lowest energy state (ie stability). In fact this return is what gives you the radiofrequencies you see as chemical shifts

Also yes increases in e- density decreases the magnetic field strength experienced by the nucleus. In uni chem this is called the shielding effect
VCE 2016-2018

2017: Biology [38], Further Maths [44]

2018: Methods [37], French [38], Chem [40], English [44]

UMAT: 56/43/80, 57th percentile (LLLLOOOOOOOOOLLLLLLLL)

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2019-2021: Bachelor of Biomedical Science at Monash (Scholars), minoring in Chemistry

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2022: Chilling

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beep boop

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Re: VCE Chemistry Question Thread
« Reply #9250 on: January 26, 2022, 08:20:40 pm »
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I've done parts a, b but not c. Can someone please explain this? Do I make a combustion equation w/ C12H24 first?
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Billuminati

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Re: VCE Chemistry Question Thread
« Reply #9251 on: January 26, 2022, 09:11:38 pm »
+2
I've done parts a, b but not c. Can someone please explain this? Do I make a combustion equation w/ C12H24 first?

I think this exact question appeared in my own chem exam (2018), I feel old now lol. Anyways, here are my workings: https://drive.google.com/file/d/1DL6s-0-drILAQL8-Zktp10xt12_k1Uky/view?usp=sharing
VCE 2016-2018

2017: Biology [38], Further Maths [44]

2018: Methods [37], French [38], Chem [40], English [44]

UMAT: 56/43/80, 57th percentile (LLLLOOOOOOOOOLLLLLLLL)

ATAR: 98.1

2019-2021: Bachelor of Biomedical Science at Monash (Scholars), minoring in Chemistry

GAMSAT September 2021: 65/67/86, 76 overall (98th percentile)

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user28

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Re: VCE Chemistry Question Thread
« Reply #9252 on: January 26, 2022, 11:54:42 pm »
0
I need help with a question!

a)What mass of iron may be extracted from 1000 tonnes of Fe3O4 according to
3Fe3O4(s)+8Al(s)-->4Al2O3(s)+9Fe(s)?

b) What mass of aluminium is used in the process?

All help would be appreciated. Thanks!  :) :)

Billuminati

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Re: VCE Chemistry Question Thread
« Reply #9253 on: January 27, 2022, 12:55:42 am »
+2
I need help with a question!

a)What mass of iron may be extracted from 1000 tonnes of Fe3O4 according to
3Fe3O4(s)+8Al(s)-->4Al2O3(s)+9Fe(s)?

b) What mass of aluminium is used in the process?

All help would be appreciated. Thanks!  :) :)

a) 1000 t = 1000 kg = 1000000 g
n(Fe3O4) = 1000000 g / 231.533 g/mol = 4319.0387547... mol
n(Fe) = 3 x n(Fe3O4)
m(Fe) = (3 x 4319.0387547... mol) x 55.845 g/mol x 1/1000 kg/g = 723.6 kg to 4 sig figs

b) n(Al) = (8/3) x n(Fe3O4)
m(Al) = (8/3) x 4319.0387547... mol x 26.98 g/mol x 1/1000 kg/g = 310.7 kg to 4 sig figs

Note that you can check if your calculations are correct or not with dimensional analysis, all units will cancel to the appropriate unit of the final answer if you did everything correctly. For example, mol cancels out mol-1 or /mol and g cancels out g-1 or /g etc
« Last Edit: January 27, 2022, 12:58:35 am by Billuminati »
VCE 2016-2018

2017: Biology [38], Further Maths [44]

2018: Methods [37], French [38], Chem [40], English [44]

UMAT: 56/43/80, 57th percentile (LLLLOOOOOOOOOLLLLLLLL)

ATAR: 98.1

2019-2021: Bachelor of Biomedical Science at Monash (Scholars), minoring in Chemistry

GAMSAT September 2021: 65/67/86, 76 overall (98th percentile)

2022: Chilling

2023+: Transfer to teaching degree

user28

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Re: VCE Chemistry Question Thread
« Reply #9254 on: January 27, 2022, 12:38:43 pm »
0
a) 1000 t = 1000 kg = 1000000 g
n(Fe3O4) = 1000000 g / 231.533 g/mol = 4319.0387547... mol
n(Fe) = 3 x n(Fe3O4)
m(Fe) = (3 x 4319.0387547... mol) x 55.845 g/mol x 1/1000 kg/g = 723.6 kg to 4 sig figs

b) n(Al) = (8/3) x n(Fe3O4)
m(Al) = (8/3) x 4319.0387547... mol x 26.98 g/mol x 1/1000 kg/g = 310.7 kg to 4 sig figs

Note that you can check if your calculations are correct or not with dimensional analysis, all units will cancel to the appropriate unit of the final answer if you did everything correctly. For example, mol cancels out mol-1 or /mol and g cancels out g-1 or /g etc


Thank you v much:)