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blogfast25
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Chemistry brain teasers! Noob Competition!
For the benefit of the many 'noobs', some of which appear genuinely keen on learning about Chemistry, I'm organising a competition with a
series 'brain teasers'.
The winner will receive £50 worth of lab wares from my store.
Answers by U2U, please. Show your reasoning. Wrong answers will not be named or shamed. Partial scores applied where applicable.
First problem, for 10 points:
<hr>
Problem:
A sample of 4.932 g is an equimolar (molar ratio = 1:1) mixture of anh. MgCO3 and another anh. Group 2 (earth alkaline metals) carbonate.
The sample is treated with an excess HCl solution and 952 ml (at STP) CO2 gas collected in a gazometer. The sample
dissolved completely.
Questions:
1. Write the reaction equation for the dissolution of a Group 2 carbonate in HCl solution. Include state symbols.
2. What is the mystery Group 2 metal most likely to be?
<hr>
Typo corrected: volume should have been stated as 952 ml (NOT 476 ml)
[Edited on 28-8-2016 by blogfast25]
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NEMO-Chemistry
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When is the closing date? I am going to have a crack at this, i like problems like this.
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blogfast25
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That will depend on participation levels and available time (mine).
Each problem will be given at least 4 days to allow max participation. In order not to drag things out and exceed average attention spans I anticipate
5 - 7 teasers in total (about 1 month competition duration).
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NEMO-Chemistry
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Great i was thinking in hours!!! Feel free to publish my answer, especially if i get it wrong!
My reasoning is more people might have a go if they see there is no shame in getting stuff wrong, having a go is what matters.
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blogfast25
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OOOOPSIE:
BIG, Big 'my bad'.
Due to a typo on my part, the volume of CO2 eluted should have been stated as 952 ml at STP, NOT 476 ml. The original question has
been edited to reflect that and is now CORRECT.
Several good answers were received but none correct, obviously due to that reason.
Due to that reason, please adjust your answers, if you can. But two members had it right and need not adjust their
calcs, they have +10 in my book. Well done both (they have been U2Ued).
In the 'egg on face competition' I've now got an UNBEATABLE lead.    
Please accept apologies.
[Edited on 28-8-2016 by blogfast25]
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j_sum1
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Thanks for doing this blogfast.
I won't enter the competition since I am not that kind of noob. (I am a noob in plenty of other areas though.)
I did do the problem and enjoyed the puzzle element of it. Nice style of question.
I might keep track of progress on this thread and pinch ideas as they come up.
J.
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blogfast25
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Quote: Originally posted by j_sum1  | Thanks for doing this blogfast.
I won't enter the competition since I am not that kind of noob. (I am a noob in plenty of other areas though.)
I did do the problem and enjoyed the puzzle element of it. Nice style of question.
I might keep track of progress on this thread and pinch ideas as they come up.
J. |
Thanks J_sum1.
Or formulate your own problem (as part of the competition, I could do with some help here)? No typos please!
[Edited on 29-8-2016 by blogfast25]
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j_sum1
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Yeah. I can probably do that.
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NEMO-Chemistry
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Now my answer makes sense!! I wont say why because it will give it away.
I couldnt work out why it fitted in one area but didnt fit in the other area  .
I will submit later once i had a chance to double check and type all my reasoning out.
Lets see if i can make it 3 correct . If it's any consolation Blogfast the
error made me read up on the ideal gas equation. So if nothing else i have ventured into previously unknown territory.
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diddi
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I might be able to help j_sum.
Beginning construction of periodic table display
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Sulaiman
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I think a clear definition of STP is required
CAUTION : Hobby Chemist, not Professional or even Amateur
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j_sum1
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I thought that was reasonably well established.
https://en.wikipedia.org/wiki/Standard_conditions_for_temper...
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Sulaiman
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try using those conditions for this definition https://en.wikipedia.org/wiki/Molar_volume
then try to find the mystery alkali earth metal atomic weight
though the question did say "most likely" so close enough I suppose.
but then why the precision in starting weight and collected volume ?
Going backwards I get 22.3855 l/mole at 'STP' ?
Since i'm sure to get flamed I'm going to re-check .....
Edit: checked .. 22.3855 l/mole at 'blogfast25's STP'
[Edited on 29-8-2016 by Sulaiman]
Yes I'm being difficult ... so would you if last thing at night you have to invent a new super-heavy alkaline earth metal
[Edited on 29-8-2016 by Sulaiman]
CAUTION : Hobby Chemist, not Professional or even Amateur
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PHILOU Zrealone
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| Quote: Originally posted by blogfast25 | OOOOPSIE:
BIG, Big 'my bad'.
Due to a typo on my part, the volume of CO2 eluted should have been stated as 952 ml at STP, NOT 476 ml. The original question has
been edited to reflect that and is now CORRECT.
Several good answers were received but none correct, obviously due to that reason.
Due to that reason, please adjust your answers, if you can. But two members had it right and need not adjust their
calcs, they have +10 in my book. Well done both (they have been U2Ued).
In the 'egg on face competition' I've now got an UNBEATABLE lead.
Please accept apologies.
[Edited on 28-8-2016 by blogfast25] |
You look more human when doing such mistakes  .
Don't blame yourself!
I have followed the cursus to become a teacher of chemical sciences for upper secondary school (pupils from 15 to 18 years old and high school or
university).
One of the hardest/tough part of the work is to make the questions for the test...because you have to think backwards and this may lead to mistakes
(example like here division instead of multiplication).
If you really want to avoid such mistakes...you'll have to take a minute to pass the test and check if you get the expected answer...then all mistakes
into the introductive text will become apparent.
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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j_sum1
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| Quote: Originally posted by Sulaiman | try using those conditions for this definition https://en.wikipedia.org/wiki/Molar_volume
then try to find the mystery alkali earth metal atomic weight
though the question did say "most likely" so close enough I suppose.
but then why the precision in starting weight and collected volume ?
Going backwards I get 22.3855 l/mole at 'STP' ?
Since i'm sure to get flamed I'm going to re-check .....
Edit: checked .. 22.3855 l/mole at 'blogfast25's STP'
[Edited on 29-8-2016 by Sulaiman]
Yes I'm being difficult ... so would you if last thing at night you have to invent a new super-heavy alkaline earth metal
[Edited on 29-8-2016 by Sulaiman] |
I suspect you have missed something as you have attempted the calculation. I am not going to try to unravel it. To do so would likely spill the
answer and I don't want to do that.
Since you have already calculated it however, it is a common shorthand that "one mole of any gas at STP occupies 22.4 litres". No in-depth knowledge
of gas laws required.
The flip side of this is, if you do discover a superheavy group 2 element, that is pretty exciting. Element 120 has not been reported yet and
Sulaimanium has a nice sound to it.
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NEMO-Chemistry
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Be careful guys please, i have the answer to both questions. BUT the reasoning needs me to add in the gas and this is something i am working on.
Please dont give clues i really need to learn this. I took STP to mean 0C (But in Kelvin) at 1Atmosphere of pressure, my trouble is i am slightly out
on another calculation.
I know this is a rounding error as its so close in every other way and nothing else is remotely as close. This is how i worked it out, but i want/need
to link my reasoning to the gas volume.
I know the question dosnt exactly tell you that the reasoning needs to include the gas, but clearly that is the intended implication of putting the
figure there.
I got my answer last night (I am pretty sure i am right) but realized i dont know how to work out the gas volume, so this i am doing now.
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DJF90
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| Quote: Originally posted by Sulaiman |
Going backwards I get 22.3855 l/mole at 'STP' ?
Since i'm sure to get flamed I'm going to re-check .....
Edit: checked .. 22.3855 l/mole at 'blogfast25's STP'
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I suspect the small difference is due to the intended meaning of STP. I've always taken it to mean 298 K and 1 Atm, but that wikipedia link suggests
it refers to 278 K (0 *C). I think blogfast needs to clarify for the benefit of all, but suspect his interpretation is the same as mine.
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blogfast25
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@Philou: haste makes waste, I didn't try and solve it myself, even though I 'always' do.
@Suleiman: in the corrected version the answer is now unequivocal. Sorry for any inconvenience caused.
Some more answers have come in.
Solution provided tomorrow. All: thanks for playing!
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Sulaiman
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I like it ...
after giving such a simplified assumption = wrong for the first quiz I thought I'd be more careful ...
CAUTION : Hobby Chemist, not Professional or even Amateur
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blogfast25
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| Quote: Originally posted by Sulaiman | I like it ...
after giving such a simplified assumption = wrong for the first quiz I thought I'd be more careful ... |
Have you sent in an answer yet?
Note to non-noobs:
Several of you chose to answer and that's perfectly ok with me: the more the merrier. But I expect any non-noob winners to be charitable and
relinquish their prize to the first noob runner up.
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aga
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What a great Puzzle !
I've had a go, but seem to have tripped up somewhere ...
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blogfast25
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A minor mistake made in good faith. Near full marks. Start training for the second lap to make up for the few lost seconds. And DON'T forget your tyre
repair kit!
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aga
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Round 2 is a low-cost boat race on car tyre innertubes !
I knew it.
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NEMO-Chemistry
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Ok my entry is in, i am not as confident as i was!! Still its a great chance to learn and alot of fun.
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NEMO-Chemistry
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Well fuffed that up!! a darn good thrashing with the noob stick required!
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