Login

Welcome, Guest. Please login or register.

March 29, 2024, 09:06:46 am

Author Topic: VCE Chemistry Question Thread  (Read 2313423 times)  Share 

0 Members and 4 Guests are viewing this topic.

xxxjss

  • Adventurer
  • *
  • Posts: 20
  • Respect: +7
Re: VCE Chemistry Question Thread
« Reply #8100 on: August 17, 2019, 09:23:35 pm »
+3
For mass spectroscopy, do we need to know how to write the equation which produces the parent molecular ions and base peaks? (something about bombarding electrons?? - it confuses me!) I saw a question on a VCAA 2010 exam, but not sure if it's within the scope of the new study design...?
And if so, could anyone provide an example of how you would write it?
Thanks
Like you said, bombarding electrons... thus electrons must be a reactant! The way I remember how to write the chemical equation of it is that you add one electron and leave with two,and as you leave with more electrons than you added a cation must be produced to balance the charges;
Take example ethanol, CH3CH2OH + e- --> [CH3CH2OH]+ + 2e-
Also, VCAA seems to like having the cation fragment surrounded by [ ] brackets when your asked to write a certain fragment
Whether or not in the scope, I find that at least being exposed to the chemical equation helps clarify what exactly goes on in that funky machine, specifically ionisation  ;D ;D ;D ;D

persistent_insomniac

  • Forum Regular
  • **
  • Posts: 88
  • Respect: +1
  • School: -------
  • School Grad Year: 2019
Re: VCE Chemistry Question Thread
« Reply #8101 on: August 18, 2019, 08:46:23 pm »
0
I just have a qs about reaction rates: if temperature is increased, does it mean that at a certain time t, there is more product produced OR does it mean that at there is the same amount of product but produced faster?

Bri MT

  • VIC MVP - 2018
  • Administrator
  • ATAR Notes Legend
  • *****
  • Posts: 4719
  • invest in wellbeing so it can invest in you
  • Respect: +3677
Re: VCE Chemistry Question Thread
« Reply #8102 on: August 18, 2019, 09:01:21 pm »
+3
I just have a qs about reaction rates: if temperature is increased, does it mean that at a certain time t, there is more product produced OR does it mean that at there is the same amount of product but produced faster?

The same total amount of product is produced and the reaction proceeds at a faster rate.

^^^111^^^

  • MOTM: JULY 2019
  • Forum Obsessive
  • ***
  • Posts: 306
  • Respect: +26
Re: VCE Chemistry Question Thread
« Reply #8103 on: August 18, 2019, 09:08:48 pm »
0
I just have a qs about reaction rates: if temperature is increased, does it mean that at a certain time t, there is more product produced OR does it mean that at there is the same amount of product but produced faster?
Hey there! To clarify your doubt it means that the amount of product is produced faster. This is due to the law of conservation of matter (Matter can neither be created nor destroyed but only transferred). This is how it  works:
As the temperature increases, the atoms of the product collide with each other rapidly(as atoms gain kinetic energy) , and this results in a reaction. To find reaction rate use arrhenius equation:

rate = k (capital a)^a*(capital b)^b
where rate is in mol dm^-3/s, k is rate constant, A and B are concentrations in mol dm^-3, a is order of reaction in respect to concentration A and b is order of reaction in respect to capital b. 
Edit: I used capital a and b since, it becomes bold when I just write A and B.  :)
« Last Edit: August 18, 2019, 09:14:36 pm by ^^^111^^^ »

jollyboat

  • Trailblazer
  • *
  • Posts: 26
  • Respect: 0
Re: VCE Chemistry Question Thread
« Reply #8104 on: August 19, 2019, 12:17:40 pm »
0
Hey guys!

I have a really basic question haha but I can't work it out :(

What type of bond exists between one of the chromium atoms and one of the oxygen atoms in a Cr2O72- polyatomic ion? I was under the impression that all the bonds within polyatomic ions were covalent, however chromium is a metal and oxygen is a non-metal so does that mean that the bond is ionic (since ionic bonds are bonds between 1 metal and 1 non-metal)?
« Last Edit: August 19, 2019, 05:31:20 pm by jollyboat »

^^^111^^^

  • MOTM: JULY 2019
  • Forum Obsessive
  • ***
  • Posts: 306
  • Respect: +26
Re: VCE Chemistry Question Thread
« Reply #8105 on: August 19, 2019, 01:39:38 pm »
+1
Hey guys!

I have a really basic question haha but I can't work it out :(

What type of bond exists between the chromium atom and the oxygen atom in a Cr2O72- polyatomic ion? I was under the impression that all the bonds within polyatomic ions were covalent, however chromium is a metal and oxygen is a non-metal so does that mean that the bond is ionic (since ionic bonds are bonds between 1 metal and 1 non-metal)?
I am pretty sure that it should be an ionic compound. Because, the molecular formula that you have given me is dichromate, and that is an ionic compound. Usually a metal and a polyatomic ion, is almost always an ionic compound. Not too sure, so it would be great if someone else can look at this :)

khai.ling

  • Adventurer
  • *
  • Posts: 6
  • Respect: 0
Re: VCE Chemistry Question Thread
« Reply #8106 on: August 20, 2019, 06:40:00 pm »
+1
Hey guys!

I have a really basic question haha but I can't work it out :(

What type of bond exists between one of the chromium atoms and one of the oxygen atoms in a Cr2O72- polyatomic ion? I was under the impression that all the bonds within polyatomic ions were covalent, however chromium is a metal and oxygen is a non-metal so does that mean that the bond is ionic (since ionic bonds are bonds between 1 metal and 1 non-metal)?

Yeah it's ionic but this is waaaaaaay out of the scope of the VCE course - see this link if you want more details.
I hope this isn't a question your school is specifically asking you :/

2016-2017: VCE (ATAR: 99.95; UMAT: 99)
2018-2020: Bachelor of Commerce (Actuarial Studies) @UniMelb

let's yeet this wheat

^^^111^^^

  • MOTM: JULY 2019
  • Forum Obsessive
  • ***
  • Posts: 306
  • Respect: +26
Re: VCE Chemistry Question Thread
« Reply #8107 on: August 20, 2019, 08:30:20 pm »
0
Yeah it's ionic but this is waaaaaaay out of the scope of the VCE course - see this link if you want more details.
I hope this isn't a question your school is specifically asking you :/
Hahah yes, that's exactly what I was thinking.
Hey guys!

I have a really basic question haha but I can't work it out :(

What type of bond exists between one of the chromium atoms and one of the oxygen atoms in a Cr2O72- polyatomic ion? I was under the impression that all the bonds within polyatomic ions were covalent, however chromium is a metal and oxygen is a non-metal so does that mean that the bond is ionic (since ionic bonds are bonds between 1 metal and 1 non-metal)?
The day you told me the question, I was like researching about ionic and covalent characters. As a thumb rule.  the larger the electronegativity difference, the more "ionic" you could say it is. Vice versa for covalent. To be exact, if the electronegativity is greater than 2, it is considered ionic, if it is less than 1.5, it is considered covalent. Does that help u enough?

pugs

  • Trendsetter
  • **
  • Posts: 122
  • Respect: +27
Re: VCE Chemistry Question Thread
« Reply #8108 on: August 22, 2019, 06:57:32 pm »
0
hey guys, this is a v simple question that i have seem to forgotten how to work out :/

how would you convert the concentration of 4% (m/m) ethanoic acid to mol/L or M?
(i've gotten an answer of 0.666..M but not too sure if it's right)

thanks! *pls forgive me*


2019 vce journal here

whys

  • VIC MVP - 2020
  • Forum Leader
  • ****
  • Posts: 722
  • Respect: +916
Re: VCE Chemistry Question Thread
« Reply #8109 on: August 22, 2019, 11:01:05 pm »
+2
hey guys, this is a v simple question that i have seem to forgotten how to work out :/

how would you convert the concentration of 4% (m/m) ethanoic acid to mol/L or M?
(i've gotten an answer of 0.666..M but not too sure if it's right)

thanks! *pls forgive me*

Molarity = mol solute/L of solution
4% concentration = for every 1000mL (1L), there is 40g ethanoic acid.
Therefore, n(CH3COOH) = mass/molar mass
= 40/60
= 2/3 mol = 0.667 mol
0.667 mol/1L = 0.667 mol/L
= 0.667 M

As per my working out, you are correct! :D
« Last Edit: August 22, 2019, 11:05:16 pm by whys »
psych [50] bio [50]
2021-2025: BMedSci/MD @ Monash

pugs

  • Trendsetter
  • **
  • Posts: 122
  • Respect: +27
Re: VCE Chemistry Question Thread
« Reply #8110 on: August 23, 2019, 06:28:33 pm »
0
Molarity = mol solute/L of solution
4% concentration = for every 1000mL (1L), there is 40g ethanoic acid.
Therefore, n(CH3COOH) = mass/molar mass
= 40/60
= 2/3 mol = 0.667 mol
0.667 mol/1L = 0.667 mol/L
= 0.667 M

As per my working out, you are correct! :D
ok thanks so much for the clarification!


2019 vce journal here

Monkeymafia

  • Victorian
  • Trendsetter
  • **
  • Posts: 104
  • Respect: 0
Re: VCE Chemistry Question Thread
« Reply #8111 on: August 24, 2019, 04:01:24 pm »
0
When finding ΔH values using calorimeters and we get to the 2nd last step as per below:

4.93 x 10^-3 mol C2H2 : 6594.5J
1 mol C2H2 : X J

Do we use 1 mol of C2H2 or 2 mol C2H2 (as per the balanced combustion equation) to find the joules produced in order to find ΔH? Is there a reason for picking one over the other?

Thanks

^^^111^^^

  • MOTM: JULY 2019
  • Forum Obsessive
  • ***
  • Posts: 306
  • Respect: +26
Re: VCE Chemistry Question Thread
« Reply #8112 on: August 24, 2019, 04:55:44 pm »
+1
When finding ΔH values using calorimeters and we get to the 2nd last step as per below:

4.93 x 10^-3 mol C2H2 : 6594.5J
1 mol C2H2 : X J

Do we use 1 mol of C2H2 or 2 mol C2H2 (as per the balanced combustion equation) to find the joules produced in order to find ΔH? Is there a reason for picking one over the other?

Thanks
I am pretty certain that the change in enthalpy using calorimetry is  1 mol of C2H2, because the change in enthaply (ΔH) is kilojoules/ per mole. We use  per mole instead of two or any, because we are trying to find the change in the internal energy (enthalpy) as a rate.

Erutepa

  • VIC MVP - 2019
  • Forum Leader
  • ****
  • Posts: 721
  • evenin'
  • Respect: +775
Re: VCE Chemistry Question Thread
« Reply #8113 on: August 28, 2019, 08:18:59 am »
0
When finding ΔH values using calorimeters and we get to the 2nd last step as per below:

4.93 x 10^-3 mol C2H2 : 6594.5J
1 mol C2H2 : X J

Do we use 1 mol of C2H2 or 2 mol C2H2 (as per the balanced combustion equation) to find the joules produced in order to find ΔH? Is there a reason for picking one over the other?

Thanks
The heat of combustion as given to you in the data booklet is the energy releases per mole of fuel. However when you're writing delta H as the enthalpy change at the end of a thermochemical equation, you wite the energy value as per mole of reaction. Thus means if 2mol of fuel react, you multiply the fuels heat of combustion by 2 to obtain the enthalpy change for the reaction. Make sure you write it as negative as the products have less energy since heat is released.
Qualifications
 > Have counted to 227
 > Can draw really good spiders
 > 2 Poet points
 > 6.5 insanipi points
 > 1 Bri MT point

alanihale

  • Forum Regular
  • **
  • Posts: 53
  • i still haven't taken my L's yet :(
  • Respect: +31
Re: VCE Chemistry Question Thread
« Reply #8114 on: August 29, 2019, 06:30:33 am »
0
I just needed some help in the department of writing methodologies. I'm confused as to how much detail needs to be added etc. Like, do I mention that I used a dropping pipette to achieve a required mass of 150.0g?? Or do I just say, the solution was poured into the beaker to attain a mass of 150.0g??
2018 - Further Maths [44]
2019 - English [45] | Spesh [hahaha] | Methods [40] | Chem [41] | Bio [40]
Atar: 98.55

Bachelor of Dental Science (Honours) @ La Trobe

---
'Hard work beats talent when talent fails to work hard'