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March 28, 2024, 10:10:22 pm

Author Topic: VCE Chemistry Question Thread  (Read 2313056 times)  Share 

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Matthew_Whelan

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Re: VCE Chemistry Question Thread
« Reply #8055 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 #8056 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 #8057 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!
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jammol7

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Re: VCE Chemistry Question Thread
« Reply #8058 on: June 28, 2019, 12:21:05 am »
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How much of the content from chem 1/2 is actually related to 3/4? I’ve heard that stuff like the history of chemistry, calculating pH, and electron configurations are unnecessary to learn about.
Thanks.
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Lear

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Re: VCE Chemistry Question Thread
« Reply #8059 on: June 28, 2019, 09:37:18 am »
+2

How much of the content from chem 1/2 is actually related to 3/4? I’ve heard that stuff like the history of chemistry, calculating pH, and electron configurations are unnecessary to learn about.
Thanks.

I’d say a decent chunk is related but a lot of it isn’t. I would pay attention to things like mole calculations, stoichiometry and analytical techniques.
You’ve heard right that the history and electron configurations aren’t very important but calculating pH can be important in some cases.
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pugs

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Re: VCE Chemistry Question Thread
« Reply #8060 on: July 02, 2019, 10:50:18 pm »
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hi, i just want to ask: are there less or more reserves of natural gas compared to oil? (i know there are less reserves of (crude) oil compared to coal)

additionally, i just wanted to checked whether these answers are correct
Q: Explain whether or not being hygroscopic is a desirable property for a diesel fuel
- it is desirable for a diesel fuel to be hygroscopic as water content needs to be low in order for efficient combustion (of biodiesel) to occur

Q: Compare the long term storability of petrodiesel and biodiesel
biodiesel can't be stored for as long as petrodiesel because it is more likely to react with atmospheric oxygen and biodegrade
(if this is correct, why can petrodiesel be stored for longer?)

thanks  :)


2019 vce journal here

colline

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Re: VCE Chemistry Question Thread
« Reply #8061 on: July 03, 2019, 02:55:01 pm »
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Are we required to rote-learn the characteristics of different types of batteries and cells?

As an example, this was from a 2018 TSSM trial exam (Q4):

"The use of lithium technology has revolutionised the use of batteries. An example is the lithium-thionyl chloride cell which delivers a massive 3.6V. Give two reasons why lithium is popular in modern cells."

Should we expect similar questions on VCAA exams too? Thanks!

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Erutepa

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Re: VCE Chemistry Question Thread
« Reply #8062 on: July 03, 2019, 03:10:05 pm »
+1
Are we required to rote-learn the characteristics of different types of batteries and cells?

As an example, this was from a 2018 TSSM trial exam (Q4):

"The use of lithium technology has revolutionised the use of batteries. An example is the lithium-thionyl chloride cell which delivers a massive 3.6V. Give two reasons why lithium is popular in modern cells."

Should we expect similar questions on VCAA exams too? Thanks!
You should know the general characteristics of galvanic cells, fuel cells and electrolytic cells, however you don't need to know about specific cells like the lithium-thionyl chloride cell.

The question you have referenced doesn't require specific knowledge on lithium cells, but rather requires knowledge of the electrochemical series and the requirements of galvanic cells.
One reason why lithium is so popular is that it is the strongest reductant, thus can produce higher voltages when utilized galvanic cells as compared to other reductants.
As for the second reason, I would say that it is relatively abundant and readily available, however I am not certain about this. Maybe someone else can be of assistance on this second point.
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Ionic Doc

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Re: VCE Chemistry Question Thread
« Reply #8063 on: July 03, 2019, 07:15:50 pm »
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Hey everyone

Just having a bit of trouble with this dilution question, any help would be appreciated, thnx in advance  :)

' The concentration of a solution of ammonia (NH3) is 1.5%(m/v). What is the molar concentration of a solution produced by diluting 25.0 mL of this solution with 250 mL of water?
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Calebark

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Re: VCE Chemistry Question Thread
« Reply #8064 on: July 03, 2019, 08:05:29 pm »
+7
Hey everyone

Just having a bit of trouble with this dilution question, any help would be appreciated, thnx in advance  :)

' The concentration of a solution of ammonia (NH3) is 1.5%(m/v). What is the molar concentration of a solution produced by diluting 25.0 mL of this solution with 250 mL of water?

First we need to find the moles present in the 25.0mL solution of 1.5% m/v NH3. We need to remember that 1.5% m/v = 1.5g of NH3 in every 100mL

We multiply our target (25.0 mL) by our current ratio (1.5 g NH3 / 100 mL ) to get 0.375 g of NH3

Using one of our favourite formulas (n=m/M), we get 0.02202 moles of NH3 in our 25.0mL solution

Remember that as we're diluting by adding water, the number of moles of solute stays the same. So we have 25.0 mL currently, and we add 250 mL to that, so we have 275 mL of solution total which contains 0.02202 moles of NH3

Using our formula for molarity (moles of solute/litres of solution = 0.02202 moles / 0.275 L), we get 0.080 mol L-1

Two sig figs, so the answer is 0.08 mol L-1

« Last Edit: July 03, 2019, 08:07:06 pm by Calebark »
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pugs

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Re: VCE Chemistry Question Thread
« Reply #8065 on: July 04, 2019, 05:04:03 pm »
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hi, i just want to ask: are there less or more reserves of natural gas compared to oil? (i know there are less reserves of (crude) oil compared to coal)

additionally, i just wanted to checked whether these answers are correct
Q: Explain whether or not being hygroscopic is a desirable property for a diesel fuel
- it is desirable for a diesel fuel to be hygroscopic as water content needs to be low in order for efficient combustion (of biodiesel) to occur

Q: Compare the long term storability of petrodiesel and biodiesel
biodiesel can't be stored for as long as petrodiesel because it is more likely to react with atmospheric oxygen and biodegrade
(if this is correct, why can petrodiesel be stored for longer?)

thanks  :)
bump 😬


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xxxjss

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Re: VCE Chemistry Question Thread
« Reply #8066 on: July 04, 2019, 06:02:55 pm »
+3
bump 😬
I'm not too sure about the reserves of natural gas, nor whether it is incredibly necessary?
Your answer to the first question is half right and contradictory; I would say that being hygroscopic is not desirable for a fuel.  Being hygroscopic encourages a high water content as hydrogen bonds are able to form with the fuel and water. With this presence of water, when the fuel is combusted, the water will absorb or 'steal' energy in order to vaporise , thus lowering the efficiency of the fuel. Less energy = bad fuel. Hence, more hygroscopic = less energy = bad fuel.

I agree with the long term storage. Concerning why petrodiesel lasts longer lies within its structure as compared to biodiesel; petrodiesel is saturated and lacks oxygen. I assume these conditions are more stable (please correct if I'm wrong!!!!!!) than the polar, unsaturated nature of biodiesel. Possessing double bonds means the molecule can take up more hydrogens, alluding that the fatty acid methyl esters in biodiesel are more keen to react than the fullhouse petrodiesel. Having skimmed over some research papers : "Much like the vegetable oils and animal fats from which biodiesel is derived, the presence of unsaturated components leads to susceptibility to oxidative degradation. [this is in U4AOS2]" I guess petrodiesel is just less reactive and vulnerable to oxidation than biodiesel as you have stated.
^^ pls double check this logic  ??? ??? ???

pugs

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Re: VCE Chemistry Question Thread
« Reply #8067 on: July 05, 2019, 04:22:21 pm »
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thanks sm for the reply xxxjss! ♡

I'm not too sure about the reserves of natural gas, nor whether it is incredibly necessary?
yeah i was thinking that we probably don't need this, but it popped up in a question given to us by our teacher

compare the remaining reserves of coal, oil and natural gas

and i couldn't really find any information in the textbook/google (unless i skipped it by accident  :-\)

Your answer to the first question is half right and contradictory; I would say that being hygroscopic is not desirable for a fuel.  Being hygroscopic encourages a high water content as hydrogen bonds are able to form with the fuel and water. With this presence of water, when the fuel is combusted, the water will absorb or 'steal' energy in order to vaporise , thus lowering the efficiency of the fuel. Less energy = bad fuel. Hence, more hygroscopic = less energy = bad fuel.
ooooh i understand it now, thanks for the explanation! yeah beforehand i had thought that if a fuel was hygroscopic then it would reduce the water content around it, but that's not the purpose lolol

I agree with the long term storage. Concerning why petrodiesel lasts longer lies within its structure as compared to biodiesel; petrodiesel is saturated and lacks oxygen. I assume these conditions are more stable (please correct if I'm wrong!!!!!!) than the polar, unsaturated nature of biodiesel. Possessing double bonds means the molecule can take up more hydrogens, alluding that the fatty acid methyl esters in biodiesel are more keen to react than the fullhouse petrodiesel. Having skimmed over some research papers : "Much like the vegetable oils and animal fats from which biodiesel is derived, the presence of unsaturated components leads to susceptibility to oxidative degradation. [this is in U4AOS2]" I guess petrodiesel is just less reactive and vulnerable to oxidation than biodiesel as you have stated.
^^ pls double check this logic  ??? ??? ???
wow thank you so much! and for your amazing research :o this helped me heaps!!
« Last Edit: July 05, 2019, 04:24:42 pm by pugs »


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eliser24

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Re: VCE Chemistry Question Thread
« Reply #8068 on: July 05, 2019, 06:01:59 pm »
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I'm revising Unit 3 for chemistry, and I'm just struggling to understand whether petrodiesel or biodiesel is hygroscopic or whether they both are. I thought only biodiesel was, but is petrodiesel also?
thank you

Rom_Dog

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Re: VCE Chemistry Question Thread
« Reply #8069 on: July 06, 2019, 10:03:27 am »
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Hey!

This is the point in the study design which your question refers to: "the comparison of the suitability of petrodiesel and biodiesel as transport fuels with reference to sources, chemical structures, combustion products, flow along fuel lines (implications of hygroscopic properties and impact of outside temperature on viscosity) and the environmental impacts associated with their extraction and production."

Petrodiesel and biodiesel both have hygroscopic properties, this means that they have the ability to absorb water. However, biodiesel is more hydroscopic than water. From my experience it'd say that a question on hygroscopic properties in the end of year exam wouldn't be more than one mark. It's important to understand that that biodiesel molecules contain an ester group which have the ability to form hydrogen bonds/dipole-dipole bonds with water which is why biodiesel is more hygroscopic than petrodiesel (which is formed entirely from non-polar hydrocarbons).

I hope this helps!

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