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NEMO-Chemistry
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Thanks for rubbing it in  , mine will be in by tonight (hopefully).
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Lefaucheux10
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have you mine DraconicAcid ?
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NEMO-Chemistry
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Go away!!!! I dont need telling everyone else has done it thank you!
dont worry i am not serious, well done for working it out.
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DraconicAcid
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I have replies from Neme, CeReUS, Lafrauchex10, aga, Sulaiman, MeshPL, PHILOU Zrealone, Zandins, nezza and ficolas. Nobody has gotten it so wrong
that I've had to pull out the N00b stick.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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ficolas
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Sending it doesnt mean getting it right anyways :s
Im having quite a lot of fun with these questions, they dont require a lot of chemistry knowledge, but they require thinking. With the stuff that we
have learned at high school, it is possible to do them, but if this was in a high school exam most of the class would fail it. Its the kind of
question I like
I remember 3 or 4 years ago, my math teacher talked with me because in an exams, I went direct to the hard question (they always had 1 hard question),
I spent too much time in it and I didnt finish the whole exam and I always did the hard question the first one xD
It was something stupid to do but I was youngh...er
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aga
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Guys. Careful. He's obviously got a new N00b stick.
Probably bigger and more durable than the last one, maybe even the N00c model.
[Edited on 31-8-2016 by aga]
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blogfast25
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Quote: Originally posted by DraconicAcid  | | I have replies from Neme, CeReUS, Lafrauchex10, aga, Sulaiman, MeshPL, PHILOU Zrealone, Zandins, nezza and ficolas. Nobody has gotten it so wrong
that I've had to pull out the N00b stick. |
When are you closing, DA?
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DraconicAcid
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In about 13 hours.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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aga
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What ? We were supposed to answer in Russian ?
Oh crap.
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NEMO-Chemistry
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Thats me in it then, i answer in double Dutch.
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aga
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Jeez. Just 11 hours to go and we had to learn Russian !
DraconicAcid is a hard task-master.
1. Мой ответ является правильным, даже если это не так, товарищ.
2. Дайте полную марок меня или я буду есть ваши хомяков - все они, один за другим
[Edited on 31-8-2016 by aga]
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DraconicAcid
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К счастью , у меня нет хомяков , так что ваши угрозы не влияют на меня .
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Texium
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Now we need Ave to show up and tell you guys that you're completely wrong because you probably just plugged stuff into Google Translate
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aga
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Run NEMO ! Run !
They're onto us already.
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NEMO-Chemistry
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Why should i run?? Wasnt me who just ordered a Sulphuric acid colonic irrigation in Russian .
Just what you boys need.....a good ole clear out lol. I have had to skip this question, I am working on Molarity and associated stuff to catch up with
the course at school. I found the question hard with my current level of knowledge.
So i have decided to not to rush this one, i would rather study it carefully and do the chemistry homework i have. I am not dropping out of the
competition though.
For me its not about winning but about learning, i have done alot of reading for the question, so hopefully when i see the answer alot of things will
click into place. Great question though, and thanks to aga for saying it made him head scratch!
After so many said it was easy i felt bad that i didnt find it so easy, so having someone who is fairly experienced say they had to work at it made me
feel better.
This really is a great way to learn, with or without the prize incentive its alot of fun.
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blogfast25
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Crrraaaaaack! (sound of long metal ruler hitting desk!)
Silence in the study room, please!
(It's always the same g-ddamn suspects, isn't it? One of 'em's only been back for half a day an'es already flirting with detention again!)
[Edited on 31-8-2016 by blogfast25]
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NEMO-Chemistry
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aga
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I spent about 3 hours on it, so yes, quite hard for a noob, which i consider myself to be.
If you imagine the whole Molecular weight thing as just how many grammes one mol of some random stuff weighs, and how much 1 litre of solvent is,
Molarity gets easier.
e.g. 1 mol of NaCl = 58.469 grammes.
Stuff 58.44 g of NaCl into 1 litre of water, and you got a 1 molar solution.
a.k.a. [1] M NaCl solution.
Then you can use C1V1= C2V2 to dilute that down to any molar concentration you want.
e.g. you need [0.5] M NaCl solution, and you got that 1 litre with 58.44g salt in it.
C1 = [1], V1=1
C2 = [0.5], V2 = ?
Do some light algebra and V2 = (C1 V1) / C2
So V2 = 1 x 1 / 0.5 = 2, so dilute it to 2 litres and it's Molarity reduces to [0.5]
Obvious going from 1 to 0.5, but the maths hold true for any desired concentration.
Oh my lord.
blogfast25 seems to have the metal N00d model stick.
Edit:
blogfast25 taught me that, hope i passed it on ok.
[Edited on 31-8-2016 by aga]
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j_sum1
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Hey. I want nothing to do with blogfast's nood stick.
[blocks ears, closes eyes]
La la la la la la la la la la
[/bece]
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blogfast25
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4 more problems will now be published. These will stay open till the end of the competition (end of this month, precise date to be published soon).
More may yet be published shortly...
Please U2U all concise answers with summarised reasoning to ME. Use the red reference number (top left) as the title of your
U2U.
Thank you for playing!
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DraconicAcid
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The deadline for my question has passed, so I guess I ought to post the solution.
3.75 g of a metal chloride is dissolved in water and treated with excess aqueous silver nitrate, resulting in the formation of 10.66 g of precipitate.
Net ionic equation: Ag+(aq) + Cl-(aq) --> AgCl(s)
We obtained 10.66 g of silver chloride, which is 74.37 mmol. *If* the metal was monovalent, that would mean the molar mass of the metal chloride was
3.75 g / 0.07437 mol = 50.4 g/mol, which would give the metal a molar mass of 15.0 g/mol. This is not the molar mass of a metal.
If it's divalent, then the molar mass of the metal chloride would be 3.75 g / (0.07437 mol/ 2) = 100.8 g/mol. Subtracting the two chlorides gives
29.9 g/mol. This is between silicon and phosphorus, which are not metals.
Trivalent gives 44.9 g/mol, which is within experimental error for scandium (which is indeed trivalent).
Tetravalent gives 59.9 g/mol, which is close to cobalt or nickel, neither of which form tetrachlorides.
Pentavalent gives 74.9 g/mol, which would be arsenic, but arsenic is not a metal, and its pentachloride is not ionic.
Hexavalent would give 89.8 g/mol, which is close to yttrium and zirconium, neither of which have a +6 oxidation state. Similarly, rhodium and
palladium do not form heptachlorides, and tin doesn't form an octachloride. So the metal must be scandium.
[Edited on 1-9-2016 by DraconicAcid]
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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blogfast25
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NC#3
(Courtesy of j_sum1)
A fertiliser is known to be a combination of ammonium sulfate, ammonium nitrate and potassium nitrate.
Distillation of 100g of the fertiliser with sulfuric acid yields 41.5g of white fuming nitric acid (100 % pure nitric acid).
Addition of excess sodium hydroxide to 100g of the fertilizer releases 15.6g of ammonia gas.
Dissolving 100g of the fertiliser in water and adding excess calcium nitrate solution gives a white precipitate. After filtering, drying and calcining
to obtain the anhydrous form, 41.2g of this precipitate is recovered.
Question:
Assume that the original fertiliser is fully dry and that there is 100% conversion for each of the tests. What is the composition of the fertiliser?
3 points per component.
[Edited on 1-9-2016 by blogfast25]
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aga
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| Quote: Originally posted by DraconicAcid | The deadline for my question has passed, so I guess I ought to post the solution.
Net ionic equation: Ag+(aq) + Cl-(aq) --> AgCl(s) |
... and Scandium (hopefully).
OK. Learning Hindi now for the next question.
Edit:
Wonderful puzzles guys ! Thanks for posting them !
[Edited on 1-9-2016 by aga]
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blogfast25
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NC#4
5.000 g of a specific hydrocarbon (CxHy) is quantitatively oxidised to CO2 and H2O. The water is caught in
a cold trap and 4.49 g of it obtained.
The CO2 is quantitatively converted to BaCO3 and 73.9 g of it obtained.
Questions:
1. What is the simplest empirical formula of the compound? (7 points)
2. Which of the following could it be? (3 points)
a. methyl benzene
b. butyl benzene
c. an isomer of trimethyl benzene
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blogfast25
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NC#5
A sample is composed of potassium alum, sodium chloride and potassium nitrate. A 30.0 g sample is fully dissolved in water. To the solution 0.300 mole
of ammonia (NH3) is added and a precipitate is formed. The solution is then filtered and the filter cake washed. Filtrate and wash water
are quantitatively recovered and the combination diluted to 250.0 ml.
Several 25.0 ml aliquots of this stock solution are titrated with 0.9915 M hydrochloric acid in an acid/base titration. A significant average of 17.4
ml of titrant solution is used.
Questions:
1. Write the ionic reaction equation of the precipitation reaction, state symbols included.
2 points.
2. What is the weight percentage of potassium alum in the sample?
8 points.
[Edited on 2-9-2016 by blogfast25]
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