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March 28, 2024, 07:41:33 pm

Author Topic: VCE Chemistry Question Thread  (Read 2312967 times)  Share 

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Phenomenol

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Re: VCE Chemistry Question Thread
« Reply #525 on: March 25, 2014, 08:52:36 pm »
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There's a difference between de-ionised water and destilled water..But are they the same? Just difference processes?
If a question asked to write steps for like...cleaning equipment..which would I use?

Thanks

As far as I know, the purity of deionised water is higher than distilled water.
Also, you shouldn't necessarily clean equipment with either water. For example, a burette with which you will fill HCl solution in.
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Re: VCE Chemistry Question Thread
« Reply #526 on: March 25, 2014, 09:10:21 pm »
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As far as I know, the purity of deionised water is higher than distilled water.
Also, you shouldn't necessarily clean equipment with either water. For example, a burette with which you will fill HCl solution in.
it's not like i'll be cleaning a concial flask with a solution?
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Phenomenol

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Re: VCE Chemistry Question Thread
« Reply #527 on: March 25, 2014, 09:18:14 pm »
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it's not like i'll be cleaning a concial flask with a solution?

If this is titration, and you're using the conical flask to hold your aliquot, correct. Clean it with water.
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Re: VCE Chemistry Question Thread
« Reply #528 on: March 25, 2014, 10:04:38 pm »
+1
The trick here is to look at the masses of elements first, not amounts. Otherwise you're doing too much work.
Total mass(H) = 2.0/18.0 * 0.551g. This gives you the mass of hydrogen in the organic compound.

Total amount(CO2) = 0.458/22.4
Then find the mass of carbon in the CO2. This gives you the mass of carbon in the organic compound.

Simply subtract these masses from 0.470g to find the mass of oxygen in the compound. From there the routine method to find an empirical formula can be used.

So, the important thing to note is that all the carbon in the original compound is now in the form of CO2, and all the hydrogen in the original compound is now in the form of H2O.

Ah i get it now. Thank you for your help.
Really appreciate it.
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Re: VCE Chemistry Question Thread
« Reply #529 on: March 26, 2014, 05:51:37 pm »
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when turning a alkene into a chloroalkane, is AlCl3 necessary or can I use just use HCL as a catalyst?
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darklight

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Re: VCE Chemistry Question Thread
« Reply #530 on: March 26, 2014, 05:55:54 pm »
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Hi guys,

Say you are doing a volumetric analysis with the unknown solution being in the conical flask and the chemical with the known concentration is in the burette. What happens if the conical flask is rinsed by accident with the unknown solution?
Because you have more mol in the conical flask than expected, you'd need more titre from the burette, so you'd calculate a higher mol and hence higher concentration than expected. Is this right?

But what happens if you switch this around, and the known is in the conical and the unknown is in the burette, but you still wash the conical flask with the unknown? Because you have some of the unknown in the conical flask, it would already react with the known which would mean you would need less titre from the burette, which would mean that you would calculate a higher concentration right?

Is this reasoning right? Thanks :)
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drake

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Re: VCE Chemistry Question Thread
« Reply #531 on: March 26, 2014, 05:57:11 pm »
+1
when turning a alkene into a chloroalkane, is AlCl3 necessary or can I use just use HCL as a catalyst?

hey sanguinne, AlCl3 is not necessary. you just need HCl - but remember HCl is NOT a catalyst. it is simply a reactant!
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Re: VCE Chemistry Question Thread
« Reply #532 on: March 26, 2014, 06:26:45 pm »
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hey sanguinne, AlCl3 is not necessary. you just need HCl - but remember HCl is NOT a catalyst. it is simply a reactant!


oh ok
thanks   :D
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Re: VCE Chemistry Question Thread
« Reply #533 on: March 26, 2014, 07:10:54 pm »
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Hi guys,

Say you are doing a volumetric analysis with the unknown solution being in the conical flask and the chemical with the known concentration is in the burette. What happens if the conical flask is rinsed by accident with the unknown solution?
Because you have more mol in the conical flask than expected, you'd need more titre from the burette, so you'd calculate a higher mol and hence higher concentration than expected. Is this right?

But what happens if you switch this around, and the known is in the conical and the unknown is in the burette, but you still wash the conical flask with the unknown? Because you have some of the unknown in the conical flask, it would already react with the known which would mean you would need less titre from the burette, which would mean that you would calculate a higher concentration right?

Is this reasoning right? Thanks :)

Your reasoning is right. Good work.
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darklight

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Re: VCE Chemistry Question Thread
« Reply #534 on: March 26, 2014, 08:16:19 pm »
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Your reasoning is right. Good work.

Thank you! Another question:
If you rinsed the conical flask that contained the unknown solution with the known solution, this would cause a lower than expected conc. of the unknown solution because some of the known will react with the unknown prior to letting the titre run? Also, what is the effect when the burette which has a known solution is rinsed with the unknown solution?

thanks :)
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Phenomenol

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Re: VCE Chemistry Question Thread
« Reply #535 on: March 26, 2014, 09:08:10 pm »
+1
Thank you! Another question:
If you rinsed the conical flask that contained the unknown solution with the known solution, this would cause a lower than expected conc. of the unknown solution because some of the known will react with the unknown prior to letting the titre run? Also, what is the effect when the burette which has a known solution is rinsed with the unknown solution?

thanks :)

Some unknown will react prior to titration -> titre will be lower -> calculated amount of unknown is lower therefore lower than expected concentration of unknown. Yep.
Ughh, in the off chance that someone is stupid enough to do this (I doubt this scenario will ever come up), the concentration of the known solution will decrease -> titre will increase -> calculated amount of unknown is higher -> higher than expected concentration of unknown.
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Re: VCE Chemistry Question Thread
« Reply #536 on: March 26, 2014, 09:47:40 pm »
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Pentane boils at 36 degrees, while 2-methylbutane boils at 28 degrees. Explain why pentane has the higher boiling point.
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Re: VCE Chemistry Question Thread
« Reply #537 on: March 26, 2014, 09:51:37 pm »
+1
2methyl butane has a methyl side group which prevents the molecules from getting close to each other. Pentane on the other hand, does not have this physical obstruction and hence, can get all nice and snuggly with each other.  The result is that the dispersion forces among the pentane would be a lot stronger because of the shorter distances between molecules.

Stronger dispersion forces = harder to evaporate using heat = higher boiling point.
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Re: VCE Chemistry Question Thread
« Reply #538 on: March 27, 2014, 05:08:20 pm »
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Devise reaction pathways for the following reactions:
a) ethylamine from ethene
Pls write why you did specific steps

Thanks ;D
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Re: VCE Chemistry Question Thread
« Reply #539 on: March 28, 2014, 07:47:43 am »
+1
See the picture below.  Look at where you start. look at where you end up, thus you find the reactions to get you there.

Devise reaction pathways for the following reactions:
a) ethylamine from ethene
Pls write why you did specific steps

Thanks ;D
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