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Author Topic: Unit 3 Questions MEGATHREAD :)  (Read 61306 times)  Share 

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luken93

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Unit 3 Questions MEGATHREAD :)
« on: March 16, 2011, 07:48:48 pm »
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So I thought I may as well start up a thread for all us 2011 Chem students to feel free to ask any theory based questions about anything relevant to Unit 3...

I figure we could all get something out of every question made, but could we please keep it to theory or Why is/does/how etc? questions only as opposed to textbook questions.
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luken93

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Re: Unit 3 Questions MEGATHREAD :)
« Reply #1 on: March 16, 2011, 07:50:40 pm »
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My first question:

Why is Cr2O72- / H+ used as a catalyst for oxidation, and what does it therefore mean having the / H+ on the bottom of the arrow in a reaction?
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Mao

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Re: Unit 3 Questions MEGATHREAD :)
« Reply #2 on: March 16, 2011, 08:56:34 pm »
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Note that: this is a reduction equation, dichromate is an oxidant, dichromate causes oxidation, thus it is used when an organic compound need to be oxidized/etc. It is not a catalyst, it is required for the reaction.

Also note that this reaction consumes protons, thus only adding dichromate is not enough. You must always have plenty of acid to go with dichromate. You almost never see a dichromate solution, it is always available as 'acidified dichromate' to activate the oxidative reaction.

The use and behaviour of permanganate is very similar.
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luken93

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Re: Unit 3 Questions MEGATHREAD :)
« Reply #3 on: March 16, 2011, 09:02:47 pm »
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aaah that makes more sense, thanks a lot!
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meli001

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Re: Unit 3 Questions MEGATHREAD :)
« Reply #4 on: March 16, 2011, 09:12:33 pm »
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Hi, this is probably going to be a pretty blonde question but with the formula c1v1=c2v2, is it possible to use ANY concentration unit in this formula? Instead of the conventional mol/L, can I use say ppm or g/ml? Thanks :)
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luken93

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Re: Unit 3 Questions MEGATHREAD :)
« Reply #5 on: March 16, 2011, 09:16:59 pm »
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Yeah you can, as long as you keep it the same for both sides
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Bozo

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Re: Unit 3 Questions MEGATHREAD :)
« Reply #6 on: March 17, 2011, 06:19:43 pm »
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Is Ba(H2PO4)2 insoluble?
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nacho

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Re: Unit 3 Questions MEGATHREAD :)
« Reply #7 on: March 17, 2011, 06:34:44 pm »
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Predict the effect of the following on the experimental value for the concentration of nitrogein in the lawn feed: would it cause it to be higher than or lower than the true value, or have no effect? Justify each answer.
-Just a headsup : This is a back titration. Reacted lawn feed solution with excess NaOH. Remaining NaOH was reacted against HCl.
Q1. The supplied value for [HCl] was lower than its true value.

Q2. The distilled water was found to have a pH of 6.0
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luken93

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Re: Unit 3 Questions MEGATHREAD :)
« Reply #8 on: March 17, 2011, 07:33:45 pm »
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Quote from: Bozo on March 17, 2011, 06:19:43 pm
Is Ba(H2PO4)2 insoluble?

Wouldn't it be an Ionic Compound? (Barium is a metal, Phosphate is a non-metal)
Therefore, it is highly polar as it has a large difference in electronegativities - hence it is soluble...

I'd wait for this to be confirmed though.
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luken93

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Re: Unit 3 Questions MEGATHREAD :)
« Reply #9 on: March 17, 2011, 07:37:54 pm »
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Quote from: nacho on March 17, 2011, 06:34:44 pm
Predict the effect of the following on the experimental value for the concentration of nitrogein in the lawn feed: would it cause it to be higher than or lower than the true value, or have no effect? Justify each answer.
-Just a headsup : This is a back titration. Reacted lawn feed solution with excess NaOH. Remaining NaOH was reacted against HCl.
Q1. The supplied value for [HCl] was lower than its true value.

Q2. The distilled water was found to have a pH of 6.0
Supplied value = Concentration?
If it is concentration, then more HCl would be required to neutralise the NaOH. As a result, you would think that more NaOH was left in excess after the first reaction, and hence a lower % of Nitrogen would be given in the lawn feed because it would seem less has reacted with it.

Q2, where was the distilled water used?
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2010: Business Management [47]
2011: English [44]   |   Chemistry [45]  |   Methods [44]   |   Specialist [42]   |   MUEP Chemistry [5.0]   |   ATAR: 99.60
UMAT: 69 | 56 | 82 | = [69 / 98th Percentile]
2012: MBBS I @ Monash

nacho

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Re: Unit 3 Questions MEGATHREAD :)
« Reply #10 on: March 17, 2011, 08:23:00 pm »
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Quote from: luken93 on March 17, 2011, 07:37:54 pm
Quote from: nacho on March 17, 2011, 06:34:44 pm
Predict the effect of the following on the experimental value for the concentration of nitrogein in the lawn feed: would it cause it to be higher than or lower than the true value, or have no effect? Justify each answer.
-Just a headsup : This is a back titration. Reacted lawn feed solution with excess NaOH. Remaining NaOH was reacted against HCl.
Q1. The supplied value for [HCl] was lower than its true value.

Q2. The distilled water was found to have a pH of 6.0
Supplied value = Concentration?
If it is concentration, then more HCl would be required to neutralise the NaOH. As a result, you would think that more NaOH was left in excess after the first reaction, and hence a lower % of Nitrogen would be given in the lawn feed because it would seem less has reacted with it.

Q2, where was the distilled water used?
i believe the supplied value is the value we're given on the label (i.e, what we are made to think) and the true value is the real concentration.
distilled water used for washing the volumetric flask (and any other places u would use distilled water to wash.

thanks
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pi

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Re: Unit 3 Questions MEGATHREAD :)
« Reply #11 on: March 17, 2011, 09:16:28 pm »
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Quote from: Bozo on March 17, 2011, 06:19:43 pm
Is Ba(H2PO4)2 insoluble?


Generally phosphates are insoluble, so I think that one will be too
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Mao

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Re: Unit 3 Questions MEGATHREAD :)
« Reply #12 on: March 17, 2011, 10:19:40 pm »
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Quote from: pi on March 17, 2011, 09:16:28 pm
Quote from: Bozo on March 17, 2011, 06:19:43 pm
Is Ba(H2PO4)2 insoluble?


Generally phosphates are insoluble, so I think that one will be too

I wouldn't be so sure. Phosphates are generally insoluble. dihydrogenphosphates, not so sure. (I have no idea whether it is soluble or not)

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« Last Edit: January 03, 2017, 12:33:03 am by pi »
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annabri

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Re: Unit 3 Questions MEGATHREAD :)
« Reply #13 on: March 19, 2011, 03:01:09 pm »
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are ion-dipole bonds stronger than hydrogen bonds? eg. in organic compounds chloroalkanes versus alkanols...

also how do i write a conclusion for an organic prac!?
short and sweet but what should it include?

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pi

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Re: Unit 3 Questions MEGATHREAD :)
« Reply #14 on: March 19, 2011, 03:03:28 pm »
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Hydrogen bonds are stronger
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