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November 12, 2019, 10:38:02 pm

Author Topic: VCE Chemistry Question Thread  (Read 987268 times)  Share 

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walnut

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Re: VCE Chemistry Question Thread
« Reply #8055 on: June 15, 2019, 03:45:27 pm »
0
Hey, so I tried doing p1v1=p2v2 but I'm not sure why but I just can't get the answer...
Thanks!

Reaction between fluorine and chlorine results in formation ofthe interhalogen CIF3.
Suppose 35.5 L of F2gas is combined with excess Cb gas (at 1 atm pressure and at 25C) and the reaction goes to completion (you can assume no. other products are formed). If all the CIF3 gas produced in the reaction is stored in a 12.5 L tank at 25C the pressure ofthe gas in the container will be closest to?
[Data: 1 mole of an ideal gas occupies 24.45 L at 1 atm and 25C]

Answer is 192kPA
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briv01

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Re: VCE Chemistry Question Thread
« Reply #8056 on: June 15, 2019, 08:06:52 pm »
+3
Hey, so I tried doing p1v1=p2v2 but I'm not sure why but I just can't get the answer...
Thanks!

Reaction between fluorine and chlorine results in formation ofthe interhalogen CIF3.
Suppose 35.5 L of F2gas is combined with excess Cb gas (at 1 atm pressure and at 25C) and the reaction goes to completion (you can assume no. other products are formed). If all the CIF3 gas produced in the reaction is stored in a 12.5 L tank at 25C the pressure ofthe gas in the container will be closest to?
[Data: 1 mole of an ideal gas occupies 24.45 L at 1 atm and 25C]

Answer is 192kPA

I did it using the standard formula. First of all, youre looking for the pressure in the container at the end meaning you need the mols of the product. I wrote a balanced equation and found that F2:ClF3 is 3:2.

Then I found the mols of F2 using n=V/Vm where n was 35.5 and Vm was 24.5. And I divided that by 3 and multiplied by 2 to find the mols of the product

Then I used that in the formula nRT/V =P. ( making sure to convert T into K, R is 8.31, V is 12.5 )


briv01

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Re: VCE Chemistry Question Thread
« Reply #8057 on: June 15, 2019, 08:14:25 pm »
+2
Heyy,
I'm also a bit unsure about what to do with this question...
I think it's mainly the 250ml of 1.0M which confuses me.
How would I convert that to moles??

For that question, the answer would actually still be the initial concentration ( 1M ) As whilst Cu ions in the electrolyte are being used up, the anode electrode is being oxidised and forming more ions.

If there wasnt a Cu anode, then what Id do is use the A and time given to find the charge and then use that to find the mols of the copper ions.

Then Id use c=n/v where v is in litres to find the concentration used of the copper solution and subtract that from the initial concentration ( 1M )

f0od

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Re: VCE Chemistry Question Thread
« Reply #8058 on: June 15, 2019, 11:54:42 pm »
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Hey, I have a few questions that I'm not sure with and was wondering if anyone would be able to help me <3

1. A steel can may be placed with tin by electrolysis in an aqueous solution containing tin ions. The equation for the plating can be represented as Sn2+ (aq) + ne- --> Sn(s)
- Name the electrolyte and give its chemical composition

--> The answer for this was tin nitrate, but I'm not sure where the nitrate came from. Is it just a chem thing where the positively charged part of the electrolyte is always paired with nitrate?

2. Carbon monoxide reacts with chlorine gas to form phosgene, COCl2. At each of the two temperatures, T1 and T2, 1.0 mol Cl2 was mixed with 1.0 mol of CO in a 1.0 L container. The concentration of COCl2 was measured as a function of time in each experiment.
The diagram of the reaction is attached below (vv sorry that the quality sucks! it was taken on photobooth lol)

a. Explain why the concentration of COCl2 reached after long reaction times is different in the two experiments, and why in both experiments the concentration of COCl2 is less than 1.0 M.

b. Deduce whether the reaction is exothermic or endothermic. Explain your reason.

Thank you so much!!!
class of 2019

briv01

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Re: VCE Chemistry Question Thread
« Reply #8059 on: June 16, 2019, 03:18:32 pm »
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For the electrolyte, you need Tin ions so they can be reduced. NO3 is used as it is inert and also its soluble and wont precipitate with the tin ions. If eg OH was used, It can form a precipitate with tin, making it insoluble and therefore not a good electrolyte ..

For the second part, Im not entirely sure. But we start off by working out which T is higher, it is evident that equilibrium is established quicker ( the curve evens out faster ) for T1, meaning it has a higher rate of reaction, meaning it must be the higher temperature.

Then we need to deduce if it is exothermic or endothermic. T2, the lower temperature, produces more products meaning there is a net forward reaction, making it an exothermic reaction ( it produces heat energy to compensate for the low temp ). T1 has a net reverse reaction instead as it is a higher temperature, producing less products.

The concentration cant go above 1M as C is n/v and both n and v are 1, making C 1

Little Miss Cocopops

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Re: VCE Chemistry Question Thread
« Reply #8060 on: June 16, 2019, 03:43:11 pm »
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Hey,
what impact does electrolyte concentration have on the amount of mass deposited on the cathode during electrolysis?
Thanks

nianid

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Re: VCE Chemistry Question Thread
« Reply #8061 on: June 16, 2019, 07:04:15 pm »
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Hey,
what impact does electrolyte concentration have on the amount of mass deposited on the cathode during electrolysis?
Thanks
For mass to be deposited on the cathode a sufficient concentration of metal ions is needed so they can be attracted to the cathode and gain electrons to  turn into a metal. It's also important to have anions to be attracted to the anode to enable the flow of electrons from the anode to the cathode, so cations of the metal can gain electrons and turn into a solid to electroplate the cathode.
I hope this makes sense  :)
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fiona_atarnotes

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Re: VCE Chemistry Question Thread
« Reply #8062 on: June 16, 2019, 09:33:29 pm »
+2
Hey, I have a few questions that I'm not sure with and was wondering if anyone would be able to help me <3

1. A steel can may be placed with tin by electrolysis in an aqueous solution containing tin ions. The equation for the plating can be represented as Sn2+ (aq) + ne- --> Sn(s)
- Name the electrolyte and give its chemical composition

--> The answer for this was tin nitrate, but I'm not sure where the nitrate came from. Is it just a chem thing where the positively charged part of the electrolyte is always paired with nitrate?

2. Carbon monoxide reacts with chlorine gas to form phosgene, COCl2. At each of the two temperatures, T1 and T2, 1.0 mol Cl2 was mixed with 1.0 mol of CO in a 1.0 L container. The concentration of COCl2 was measured as a function of time in each experiment.
The diagram of the reaction is attached below (vv sorry that the quality sucks! it was taken on photobooth lol)

a. Explain why the concentration of COCl2 reached after long reaction times is different in the two experiments, and why in both experiments the concentration of COCl2 is less than 1.0 M.

b. Deduce whether the reaction is exothermic or endothermic. Explain your reason.

Thank you so much!!!

Hey!

In response to your quesions
1. For electroplating cells we know that the electrolyte must always contain the ion of the metal that undergoes reduction on the cathode. In this scenario, the cathode is the steel can and we want tin to be plated on it. Therefore, the electrolyte must contain the tin ion, Sn2+. Recall that the electrolyte must always be made up of positive and negative charges so we currently have the positive ions, Sn2+ but we need the negative ions. The negative ions could really be anything so long as it doesn't form a precipitate with Sn2+, and since the nitrate ion tends to always form a soluble salt then a likely option for the electrolyte is tin nitrate.

2. a) We expect the concentration of COCl2 to be less than 1.0 M because if this were true then that means that the reaction goes to completion where all of the CO and Cl2 is used up. However, this this is an equilibrium reaction, we know that the concentration of CO and Cl2 only decreases to some extent, but not fully. Therefore, we also expect the concentration of COCl2, to increase by the same proportion in which CO and Cl2 decrease.

b) Does the question tell you which temperature T1 or T2 is higher/lower? If not, I presume that T2 is a higher temperature than T1 just because it appears that the gradient of the curve corresponding to T2 is initially steeper than T1 (gradient on a concentration-time graph corresponds to the rate of reaction), and we know that higher temperature is associated with a greater rate of reaction. With that in mind, we can see that the yield of COCl2 is higher when temperature is at T1 than T2 so this must mean that at a lower temperature, the forward reaction is favoured so therefore the reaction is exothermic.

Hope this helps/makes sense!

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f0od

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Re: VCE Chemistry Question Thread
« Reply #8063 on: June 16, 2019, 10:10:32 pm »
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For the electrolyte, you need Tin ions so they can be reduced. NO3 is used as it is inert and also its soluble and wont precipitate with the tin ions. If eg OH was used, It can form a precipitate with tin, making it insoluble and therefore not a good electrolyte ..

For the second part, Im not entirely sure. But we start off by working out which T is higher, it is evident that equilibrium is established quicker ( the curve evens out faster ) for T1, meaning it has a higher rate of reaction, meaning it must be the higher temperature.

Then we need to deduce if it is exothermic or endothermic. T2, the lower temperature, produces more products meaning there is a net forward reaction, making it an exothermic reaction ( it produces heat energy to compensate for the low temp ). T1 has a net reverse reaction instead as it is a higher temperature, producing less products.

The concentration cant go above 1M as C is n/v and both n and v are 1, making C 1

wow thank you so much!! <3 lifesaver
class of 2019

f0od

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Re: VCE Chemistry Question Thread
« Reply #8064 on: June 16, 2019, 10:11:37 pm »
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Hey!

In response to your quesions
1. For electroplating cells we know that the electrolyte must always contain the ion of the metal that undergoes reduction on the cathode. In this scenario, the cathode is the steel can and we want tin to be plated on it. Therefore, the electrolyte must contain the tin ion, Sn2+. Recall that the electrolyte must always be made up of positive and negative charges so we currently have the positive ions, Sn2+ but we need the negative ions. The negative ions could really be anything so long as it doesn't form a precipitate with Sn2+, and since the nitrate ion tends to always form a soluble salt then a likely option for the electrolyte is tin nitrate.

2. a) We expect the concentration of COCl2 to be less than 1.0 M because if this were true then that means that the reaction goes to completion where all of the CO and Cl2 is used up. However, this this is an equilibrium reaction, we know that the concentration of CO and Cl2 only decreases to some extent, but not fully. Therefore, we also expect the concentration of COCl2, to increase by the same proportion in which CO and Cl2 decrease.

b) Does the question tell you which temperature T1 or T2 is higher/lower? If not, I presume that T2 is a higher temperature than T1 just because it appears that the gradient of the curve corresponding to T2 is initially steeper than T1 (gradient on a concentration-time graph corresponds to the rate of reaction), and we know that higher temperature is associated with a greater rate of reaction. With that in mind, we can see that the yield of COCl2 is higher when temperature is at T1 than T2 so this must mean that at a lower temperature, the forward reaction is favoured so therefore the reaction is exothermic.

Hope this helps/makes sense!
skdjsd thank u so so much! i finally understand it now <3
class of 2019

Yemily

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Re: VCE Chemistry Question Thread
« Reply #8065 on: June 19, 2019, 12:08:51 pm »
0
Hey guys,

Does anyone have any tips/tricks for figuring out if a molecule has structural isomers and/or stereoisomers? Also, if you know a molecule has isomers, is there a way to quickly figure out how many there are? Since I struggle with visualising the structure in my head, I always have to draw the molecule(s) out and that just takes too much time.

Thanks in advance! :)

rani_b

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Re: VCE Chemistry Question Thread
« Reply #8066 on: June 24, 2019, 08:44:33 pm »
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hey guys!

So this is a question about my EPI! We are investigating the rate of reaction by changing surface area, so we expect that using smaller solids will increase rate of reaction. So we definitely got a faster rate of reaction using smaller solids compared to larger ones (we measured the volume of gas released to check over set time intervals) but our graph, which is volume of gas released against time, is like a steadily increasing exponential curve rather than the backwards L shape it should be? Can anyone think of why more volume of gas was released later on in the reaction rather than at the start like it should be predicted (like experimental errors?) I'm so confused!!

If you don't get my explanation, I've attached a photo:
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Matthew_Whelan

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Re: VCE Chemistry Question Thread
« Reply #8067 on: June 24, 2019, 09:16:57 pm »
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hey guys!

So this is a question about my EPI! We are investigating the rate of reaction by changing surface area, so we expect that using smaller solids will increase rate of reaction. So we definitely got a faster rate of reaction using smaller solids compared to larger ones (we measured the volume of gas released to check over set time intervals) but our graph, which is volume of gas released against time, is like a steadily increasing exponential curve rather than the backwards L shape it should be? Can anyone think of why more volume of gas was released later on in the reaction rather than at the start like it should be predicted (like experimental errors?) I'm so confused!!

If you don't get my explanation, I've attached a photo:

Hi so I could be wrong but it looks as if the rate of the forward reaction is approaching equilibrium. This would explain the decline into a constant rate. The rate won't steadily increase as the quantity of the solid decreases as the gas is released and so the rate will slow down.
Hope this helps!
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persistent_insomniac

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Re: VCE Chemistry Question Thread
« Reply #8068 on: June 26, 2019, 04:54:45 pm »
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Can someone please explain why the boiling point increases from amines to alcohols, to acids, to amides? I know they are have H bonding but is it the no. of H bonds each of them have that increases their boiling point and also how many hydrogen bonds do each form? I'm seriously so stuck with hydrogen bonding.

rani_b

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Re: VCE Chemistry Question Thread
« Reply #8069 on: June 26, 2019, 07:35:14 pm »
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Hi so I could be wrong but it looks as if the rate of the forward reaction is approaching equilibrium. This would explain the decline into a constant rate. The rate won't steadily increase as the quantity of the solid decreases as the gas is released and so the rate will slow down.
Hope this helps!

Hey, thanks for the reply! I understand that but the problem is that our graph did not appear to be like that, for some reason our rate was actually increasing  :o as shown on the exponential curve. I'm a bit flummoxed as to why, and I have to write a discussion about it!
2018: Psychology [50]