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September 17, 2019, 08:11:04 am

Author Topic: VCE Chemistry Question Thread  (Read 930646 times)  Share 

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Bri MT

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Re: VCE Chemistry Question Thread
« Reply #8115 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.
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Re: VCE Chemistry Question Thread
« Reply #8116 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

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Re: VCE Chemistry Question Thread
« Reply #8117 on: August 19, 2019, 12:17:40 pm »
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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 »

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Re: VCE Chemistry Question Thread
« Reply #8118 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

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Re: VCE Chemistry Question Thread
« Reply #8119 on: August 20, 2019, 06:40:00 pm »
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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 :/

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Re: VCE Chemistry Question Thread
« Reply #8120 on: August 20, 2019, 08:30:20 pm »
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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

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Re: VCE Chemistry Question Thread
« Reply #8121 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*
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whys

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Re: VCE Chemistry Question Thread
« Reply #8122 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
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pugs

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Re: VCE Chemistry Question Thread
« Reply #8123 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!
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Monkeymafia

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Re: VCE Chemistry Question Thread
« Reply #8124 on: August 24, 2019, 04:01:24 pm »
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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

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Re: VCE Chemistry Question Thread
« Reply #8125 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.

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Re: VCE Chemistry Question Thread
« Reply #8126 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.
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Re: VCE Chemistry Question Thread
« Reply #8127 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??
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Re: VCE Chemistry Question Thread
« Reply #8128 on: August 29, 2019, 07:59:44 am »
+1
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??

If you listed something in the ‘materials’ section of your prac report, then you must talk about how it’s used in the method. So yes you would need to give that amount of detail. ^-^
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Re: VCE Chemistry Question Thread
« Reply #8129 on: August 31, 2019, 06:17:14 pm »
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Hi everyone,

I am having trouble figuring out what to do as my research topic. I have been told by my teacher that it has to involve energy but still cant figure out what would be relatively easy to do.