ATAR Notes: Forum
VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: stonecold on May 25, 2010, 07:55:22 pm
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Has anyone done it?
What did you think of it?
For me, its been by far the best prac exam i've done so far. :)
Don't know whether that just means it was easy or if I'm actually improving haha!
But I still have a few questions.
Can someone please explain multi choice questions 10 and 15.
Also with short answer question 2, the answers should be in two sig figs yeah? The question only says 1.5g, yet the answers give three sig figs...
And with question 6, is phenol a functional group in salycilic acid? i.e. the benzene ring?
Thanks.
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I would argue that Phenol is a functional group.
I doubt the answer to Question 11. The answer should be C, not A.
Question 5Bi - Sooo freakin ambiguous! I really doubt this will be on a real exam.
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Nah, 11 is definitely A dj. :)
And 5.bi was okay too. I just forgot to mention the PCR...
Instead I said denaturation, annealation and elongation...
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Explain 11 then.
My logic is because its next to ANY hydrogen in an ajoining carbon, it will cause splitting.
Just because they are equivalent, I dont think this would change splitting patterns.
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Ahhh, I get where you are coming from. I dunno, maybe it does effect the peak splitting...
It is called 1,2-dihydroxyethane. Can anyone find the NRM NMR spectrum?
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I believe its an NMR spectrum. Not an NRM =P
Currently installing chemical detectives. I thought it was already on my computer, but apparently its not.
Will get spectrum of it soon.
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lol, nrm...how lame. that would be great. at least we can get the real answer :)
where do you get the program from may I ask?
dw, its sweet, i found it :)
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Phenol is not just the benzene ring, but also contains the hydroxyl group.
Multi 10: Choose the strongest base!
Question 15 can be answered by elimination. B and C are obviously wrong (ethane cannot react to form an amine) and the reaction with ethanol requires a catalyst such as alumina, making D wrong. Therefore A is correct.
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^ back to learning my reactions mind map properly :P
I get that the SO4 and NO3 are acids, but how do you know NH4+ is weaker than CO3?
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^ back to learning my reactions mind map properly :P
I get that the SO4 and NO3 are acids, but how do you know NH4+ is weaker than CO3?
Sodium sulfate and sodium nitrate are not acids. And NH4+ is an acid, not a base. :)
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^ back to learning my reactions mind map properly :P
I get that the SO4 and NO3 are acids, but how do you know NH4+ is weaker than CO3?
Sodium sulfate and sodium nitrate are not acids. And NH4+ is an acid, not a base. :)
Aaargh I'm all confused now. How do you what is an acid or a base if there is no H+ or OH- present.
Sorry, I've never been taught this stuff.
edit: And why am I only installing this Chem Detective stuff now! I could have used this for the past 3 months whilst I haven't been understanding all this spectroscopic stuff. :( ah well, better late than never...
edit 2: umm, maybe you don't get the peak splitting because the molecule is symmetrical, and the proton environments are the same, so the interference from each of the H+ environments cancel each other out...
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^ back to learning my reactions mind map properly :P
I get that the SO4 and NO3 are acids, but how do you know NH4+ is weaker than CO3?
Sodium sulfate and sodium nitrate are not acids. And NH4+ is an acid, not a base. :)
Aaargh I'm all confused now. How do you what is an acid or a base if there is no H+ or OH- present.
Sorry, I've never been taught this stuff.
That's OK. I'll (try to) explain.
NH4+ is an acid because it has the ability to donate a proton to become NH3.
Metal Carbonates able to accept a proton, and can react with acids to form a salt, carbon dioxide and water.
Nitrates and sulfates are weak bases (conjugates of strong acids).
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Also, OH groups do not cause peak splitting "for reasons beyond the scope of the course".
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NH4+ readily donates a proton to become the more stable NH3 and hence can act as an acid. Correct me if I'm wrong.
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fady_22: Not beyond the course - splitting only occurs if atoms are 3 away.
H to the O to the C. thats it. BUT will cause a peak if its water because its H to the O to the H.
[IMG]http://img683.imageshack.us/img683/1637/ethandiol.th.png[/img]
Admittedly I was wrong. But can someone explain the chemistry behind this?
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Tbh azn_dj, I think because they are symmetrical, the interferences cancel each other out, hence there are no peak splits...
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Question 11. there are two H environments, both the environments are adjacent to O so two singlets.
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excuse my ignorance, but how do you pick molecules in this program?
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err..... I have no idea tbh.....
I just went through them until I found ethandiol
lol.
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O shields the H in OH from splitting. This is because it has a high electron density, and nuclear charge of H in OH cannot penetrate this electron density, thus it does not resonate with other nearby H environments.
Also, it is not true that splitting only occurs with other nucleus 3 bonds away. There are J4 splitting in substituted arenes, and J2 splitting in phosphorus-substituted hydrocarbons and metallic complexes. None of these should mean anything to you right now, but the point is don't make up rules and reasons just because, there are lots of physical principles behind chemistry. :) [e.g. the n+1 rule is based on combinatorics (specifically pascal's triangle) in probability, multiplicity often simplifies to n+1 because difference in splitting frequency is tiny, and more often than not addition of ordinates give almost the exact same curve as n+1 would predict]
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O shields the H in OH from splitting. This is because it has a high electron density, and nuclear charge of H in OH cannot penetrate this electron density, thus it does not resonate with other nearby H environments.
Also, it is not true that splitting only occurs with other nucleus 3 bonds away. There are J4 splitting in substituted arenes, and J2 splitting in phosphorus-substituted hydrocarbons and metallic complexes. None of these should mean anything to you right now, but the point is don't make up rules and reasons just because, there are lots of physical principles behind chemistry. :) [e.g. the n+1 rule is based on combinatorics (specifically pascal's triangle) in probability, multiplicity often simplifies to n+1 because difference in splitting frequency is tiny, and more often than not addition of ordinates give almost the exact same curve as n+1 would predict]
Oh that is as romantic as a valentines day card Mao!
Marry me! That was beautiful! :smitten:
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/me raises eyebrow
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hahaaha your just awesome.... just my wonky way of saying it.
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Also, it is not true that splitting only occurs with other nucleus 3 bonds away.
I meant with a Carbon. This was what TSFX said.
So..... blame TSFX, maybe?
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anyone done the 2008 sample paper?
how did you find it. i thought it was probably too easy, and too short.
stupid mistakes always kill me though!
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Only VCAA ive done is 2009. Which i actually found alright. Maybe its because i already knew it was going to be long before i did it but i still did it to time and managed to get 88% which i was happy with. Only one that stumped me was the stoich one with the polyunsaturated hydrocarbon :S
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I reckon the 2008 VCAA one was pretty easy too...planning on doing the 09 paper today...
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That's a good score. I got 83% on that...the stupid AAS question destroyed me at the end. I found the polyunsaturated hydrocarbon question okay, accept that I bloody divided when I was supposed to multiply. :(
It was so stupid, I did it at like 10:30pm on a Sunday. Really should save those good papers for when I am more alert...
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yeah lol. i did a physics exam last night at like 10pm and marked it this morning. made the worst mistakes, like typing things in the calculator wrong haha.
Yeah the last aas question was pretty difficult. I actually had the answer right for the mass of whatever then when i was going back over it i changed it by multiplying by 10 instead of 4 ><.
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I reckon the 2008 VCAA one was pretty easy too...planning on doing the 09 paper today...
Are you talking about the sample or the actual exam?
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yeah lol. i did a physics exam last night at like 10pm and marked it this morning. made the worst mistakes, like typing things in the calculator wrong haha.
Yeah the last aas question was pretty difficult. I actually had the answer right for the mass of whatever then when i was going back over it i changed it by multiplying by 10 instead of 4 ><.
Yeah, that question was really tough. They like incorporated the theory in back titrations, gravimetric analysis and sepctroscopy all into the final question!
I've been practising AAS lately and I think it is more clear know though. :)
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Actual one.
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^oh, I was talking about the sample one lol...
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=/ I don't bother doing trial exams unless I can do them in an uninterrupted 90 minute sitting where my mind is at its peak.
It works lol, I haven't made very many stupid mistakes in the last few trial exams I've done.
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And with the AAS question at the end of 2009 VCAA, all you have to do with those kinds of questions is to convert the block of text into a flow diagram with arrows.
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^oh, I was talking about the sample one lol...
lol i know, i agreed and added that the actual was pretty easy too :P
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That was the hardest exam I've done (2009 VCAA). got 80%, maaaan better practice the questions I had trouble with, i Have a feeling we'll have to use the techniques needed again this year ><.
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Really, I honestly didn't mind it. I think VCAA make pretty good exams for chem. The two I have done so far have had very good questions, all fair game within the study design.
Good and challenging, but not too difficult, especially if you just link everything back to the concepts which are outlined in the study design.
I'm livid that I didn't get 90%+ on the 2009 VCAA, because I honestly didn't think it was that hard.
That is why we practice though... :)
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What are some other 'good' prac exams people can recommend? I'm yet to try neap and i see they're frequently recommended as good ones, but are there any others out there that have really challenged you?
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Just did Lisachem 2010; it's another long and hard exam.
=/ Lol I want to get 100% on a trial exam at least once before exams >.<
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Just did Lisachem 2010; it's another long and hard exam.
=/ Lol I want to get 100% on a trial exam at least once before exams >.<
THIS will never happen to ME! LOL! highest was 80% D:
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Just did Lisachem 2010; it's another long and hard exam.
=/ Lol I want to get 100% on a trial exam at least once before exams >.<
Me too haha! Atm, my best is 3-4 marks lost. Chemistry is so anal. Between states and Sig Figs, your almost guaranteed to lose at least a mark. :(
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Just did Lisachem 2010; it's another long and hard exam.
=/ Lol I want to get 100% on a trial exam at least once before exams >.<
glad I'm not the only one that found it hard...I know you probably didn't do as bad as me but hearing that from you gives me some relief lol.
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Just did Lisachem 2010; it's another long and hard exam.
=/ Lol I want to get 100% on a trial exam at least once before exams >.<
Me too haha! Atm, my best is 3-4 marks lost. Chemistry is so anal. Between states and Sig Figs, your almost guaranteed to lose at least a mark. :(
correct sigfigs ugh i hateeee ittttttttttttttt!!!!!!!!!!!
sigfigs lol sounds like a fruit :D
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Just did Lisachem 2010; it's another long and hard exam.
=/ Lol I want to get 100% on a trial exam at least once before exams >.<
Me too haha! Atm, my best is 3-4 marks lost. Chemistry is so anal. Between states and Sig Figs, your almost guaranteed to lose at least a mark. :(
Mmm for me it's neglecting to include key words or concepts that costs me most of my marks. Anything that is totally mathematicaly I am fine with =/
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Anyone else make a vow to never touch a TSFX prac exam?
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o0o0o how do you mean?
I was struggling big time with AAS/UV-Vis problems, but I think I've finally got my head around it.
The only thing I'm worried about is if they ask us to describe fractional distillation. What would you say...
-Mixture of compounds are placed in the fractioning column, and heated.
-Lower boiling point compounds vaporise at the top of the column, and condense, whilst higher boiling point compounds will remain towards the bottom of the column.
-Once the boiling point for a particular compound is reached at the top of the column, the fraction is removed.
-The temperature at the top of the column constantly increases, with fractions removed at their respective boiling points, until all the compounds within the column have been separated, from lowest b.p. (lowest molar mass, as there are less dispersion forces) to highest b.p. (highest molar mass, as there are the most dispersion forces)
Is that okay, have I missed anything?
A question on how a sample of DNA would be prepared for analysis would be nice.
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Like working out amounts or masses or volumes or concentrations, drawing structural/semistructural formulas, naming compounds, working out stuff from spectrums, multiple-choice, anything that doesn't involve explanation lol.
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^ yeah, like what don't you like explaining haha! probably should have made it clearer.
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I don't mind it =/ It's just the easiest place to lose marks in my opinion.
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yeah explaining concepts just reminds me of biol last year where you had to prepare certain responses for certain questions lol haha and had to make sure you mentioned certain things.
but thankfully there isnt really much like that in chem.
Only theory in aos1 is pretty much errors in techniques, and how the varying spectroscopy/chromatography work qualitatively and quantitatively.
aos2 you get a bit more about properties of hydrocarbons, reaction pathways, enzymes, distillation, macromolecules and the sort.
thats all i can think of at the moment; but apart from this its all your theory and calculations based around stoich
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Anyone done NEAP 2009?
I just did it, thought it was pretty intense, and took me the full time to do it. Not as bad as the 2010 one though.
Question 1 short answer part a had me all wtf until I finally got it in like the final 3 minutes haha...
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Did it in class today...wasn't too bad, lol the first one I couldn't do at all, then last few minutes used some logic jotted some shit down and got Se2+...and it was right lol. Didn't even use ratios...can't even remember how I did it lol
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Ratios. That was all it was haha.
The mol of Se was half of the mol Cr.
So I did this little equation thing:
2Cr2+ + Se4+ ---> 2Cr3+ + Sex
x has to equal +2 for the charges to balance... :)
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lol I was 100% positive I needed to calculate the ratios...I just didn't see how that would help ><. but now I know lol, that's pretty smart on your part :P.
I think I lost about 8 marks on that exam...I'm planning on venturing into Lisachem 09 now...lol wish me luck, and pray I make it out alive...
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Ratios. That was all it was haha.
The mol of Se was half of the mol Cr.
So I did this little equation thing:
2Cr2+ + Se4+ ---> 2Cr3+ + Sex
x has to equal +2 for the charges to balance... :)
Yeah my reasoning was similar, although I had the oxidation equation which told me that 1 electron was given away, but given the ratio meant 2 were, and if 2 were given away, 2 must be mopped up by the janitor (ie the Se4+). When this happened, then Se2+ is created. So +2.
Anyone done NEAP 2009?
I just did it, thought it was pretty intense, and took me the full time to do it. Not as bad as the 2010 one though.
Question 1 short answer part a had me all wtf until I finally got it in like the final 3 minutes haha...
Not so much as intense, but fair. The questions were quite out there. Just needed to think a bit. I actually find this paper much better than 2010, in terms of representativeness.
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Maybe it's because I'm sick, but papers have been taking me a little longer in the past couple of days, so I'm probably finding them harder than I should. This has been my best paper so far all year though. I was actually quite stoked when I was marking it haha...
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Lisachem wasn't hard O.o.
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I've heard lisachem 2010 was pissweak, but 09 was fairly good with some ridiculous questions on there.
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I just did 09, wasn't that difficult.
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No papers are really that difficult. They all test the same shit. Just worded a thousand different ways...
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lol I will never believe that after having done NEAP 2010.
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Hmm when some question says something like "what are the products" Do you assume only reacts once? Like in ethane+Cl2 do you assume no CH3CHCl2 forms since only 1 reaction..?
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Nahh, the reaction keeps on happening. So you get chloro, then dichloro, then trichloro etc.
Well, that was the question on NEAP 2009 anyway...
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did lisachem 2010 today. MC raped me and i only got 14/20 =/ . but SA was really quite easy i thought. Still relatively pleased with a 68/76
I plan to do either neap or lisachem 09 tomoz.
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OK serious question:
How do you determine the indicator suitable for a acid base titration?
I first thought you just look at reactants...the end point is approximately the solution added e.g. if you are adding weak base the pH would be around 7-9
But apparently you look at the products and determine the strength of acid base products e.g. HCl+NH3=>NH4+ + Cl- (weak acid and strong base) no idea how to predict that really...
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Does COO- Hbond with water or ion-dipole?
Is the NMR spec for CH3-CH2-CH2-CH3 just a quartet and triplet?
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Does COO- Hbond with water or ion-dipole?
Is the NMR spec for CH3-CH2-CH2-CH3 just a quartet and triplet?
the nmr spec is a triplet of a quartet (so a 12tet) for the middle ch2 hydrogens and a triplet for the terminal ch3 hydrogens
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Does COO- Hbond with water or ion-dipole?
Is the NMR spec for CH3-CH2-CH2-CH3 just a quartet and triplet?
the nmr spec is a triplet of a quartet (so a 12tet) for the middle ch2 hydrogens and a triplet for the terminal ch3 hydrogens
incorrect. The CH2 group is not split by CH2 because they are the same environment. CH2 is only split by CH3, thus it is a quartet.
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Ok so just consider half the molecule if there is a symmetrical one then>
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Does COO- Hbond with water or ion-dipole?
Is the NMR spec for CH3-CH2-CH2-CH3 just a quartet and triplet?
the nmr spec is a triplet of a quartet (so a 12tet) for the middle ch2 hydrogens and a triplet for the terminal ch3 hydrogens
incorrect. The CH2 group is not split by CH2 because they are the same environment. CH2 is only split by CH3, thus it is a quartet.
*bows down to mao*
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Volumetric analysis question on Lisachem short answer 2008 = DOG ACT!
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300 ml of a 0.35 M 2 Ca(OH) solution was reacted with 300 ml of 0.40 M HCl .
The pH of the resultant solution is closest to:
A 0.82
B 1.12
C 12.88
D 13.18
I got a pH of 12.95 is that correct? So the closest would be C but the answer is D?
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It is Ca(OH)2
That is why your getting the wrong answer. :P
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300 ml of a 0.35 M 2 Ca(OH) solution was reacted with 300 ml of 0.40 M HCl .
The pH of the resultant solution is closest to:
A 0.82
B 1.12
C 12.88
D 13.18
I got a pH of 12.95 is that correct? So the closest would be C but the answer is D?
Can you even have Ca(OH)? Shouldn't it be Ca(OH)2 in which I got pH of 12.88 using it so the answer still isn't D. o-o
I don't even know what I'm doing anymore, argh.
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[OH-]=2*0.35
pOH= -log(0.7) = 0.155
Therefore pH=14-0.155= 13.86 (which is more than they give but IDK, i probably did something wrong)
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n(OH-)=0.21
n(H+)=0.12
0.21-0.12=0.09 mol of OH-
C(OH-)=0.09/0.6=0.15
C(H+)=10^(-14)/0.15
-log(10^(-14)/0.15)=13.18
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Ahh, I didn't read the question (again)
I just found the pH of Ca(OH)2
wouldn't have got it anyway don't think.
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n(OH-)=0.21
n(H+)=0.12
0.21-0.12=0.09 mol of OH-
C(OH-)=0.09/0.6=0.15
C(H+)=10^(-14)/0.15
-log(10^(-14)/0.15)=13.18
Thanks :3
Sorry to turn this into a question thread but
An aqueous solution of potassium dichromate has a clear orange colour.
The answers say that during UV Vis, it absorbs blue light and allows orange to pass through, i thought it reflected the orange light? :/ thus measuring the amount of blue that passed through the solution (wasn't absorbed)
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n(OH-)=0.21
n(H+)=0.12
0.21-0.12=0.09 mol of OH-
C(OH-)=0.09/0.6=0.15
C(H+)=10^(-14)/0.15
-log(10^(-14)/0.15)=13.18
Thanks :3
Sorry to turn this into a question thread but
An aqueous solution of potassium dichromate has a clear orange colour.
The answers say that during UV Vis, it absorbs blue light and allows orange to pass through, i thought it reflected the orange light? :/ thus measuring the amount of blue that passed through the solution (wasn't absorbed)
yeah, the solution of an orange colour will be:
-absorbing blue light
-reflecting orange light as it is not absorbing this, so if orange light is shined onto it, since it cannot absorb this light then it will just pass through.