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November 01, 2025, 11:36:22 am
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Author Topic: Chemistry 3/4 2013 Thread  (Read 448755 times)  Share 

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thushan

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Re: Chemistry 3/4 2013 Thread
« Reply #420 on: February 10, 2013, 11:17:33 pm »
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Quote from: LOLs99 on February 10, 2013, 11:10:51 pm
Ques:  A hydrocarbon on complete combustion gives a mass of carbon dioxide which is 20/9 times greater than the mass of water produced.  What is the empirical formula of the hydrocarbon?


Assume that 9 g of water is produced and 20 grams of CO2 is produced. Go from there :)
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LOLs99

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Re: Chemistry 3/4 2013 Thread
« Reply #421 on: February 12, 2013, 12:31:14 am »
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I'm not sure. Do u just find the moles? I got C11H10..
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Bad Student

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Re: Chemistry 3/4 2013 Thread
« Reply #422 on: February 12, 2013, 07:38:34 pm »
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Is the answer ?

Working out in the spoiler
Spoiler





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Re: Chemistry 3/4 2013 Thread
« Reply #423 on: February 12, 2013, 08:18:30 pm »
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aaghh?!
I'm getting C5H11?  :o
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pi

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Re: Chemistry 3/4 2013 Thread
« Reply #424 on: February 12, 2013, 08:25:00 pm »
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Quote from: Bad Student on February 12, 2013, 07:38:34 pm
Working out in the spoiler
Spoiler






Sorry mate, second line isn't to enough decimal places.
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Bad Student

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Re: Chemistry 3/4 2013 Thread
« Reply #425 on: February 12, 2013, 08:31:26 pm »
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Quote from: pi on February 12, 2013, 08:25:00 pm
Sorry mate, second line isn't to enough decimal places.

Damn, I always make that mistake.
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Jeggz

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Re: Chemistry 3/4 2013 Thread
« Reply #426 on: February 12, 2013, 08:35:03 pm »
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hold on..so what exactly is the answer guys?  :o
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Re: Chemistry 3/4 2013 Thread
« Reply #427 on: February 12, 2013, 08:43:47 pm »
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I got C9H10, did exactly what bad student did except multiple mole of h20 by 2.

Why did you do that btw? :)
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Re: Chemistry 3/4 2013 Thread
« Reply #428 on: February 12, 2013, 08:45:34 pm »
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Quote from: Machan on February 12, 2013, 08:43:47 pm
I got C9H10, did exactly what bad student did except multiple mole of h20 by 2.

Why did you do that btw? :)

But we know that the C:H ratio is 5/11 : 1 right? and so you would multiply by it by 11?
or am i just doing something completely and utterly stupid here?  ???
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Re: Chemistry 3/4 2013 Thread
« Reply #429 on: February 12, 2013, 08:47:18 pm »
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Quote from: Machan on February 12, 2013, 08:43:47 pm
I got C9H10, did exactly what bad student did except multiple mole of h20 by 2.

Why did you do that btw? :)

The information provided allows you to find the number of mole of water, but there are two hydrogen atoms in water so I multiplied it by two.

Also, if the formula is C9H10, you're left with lots of carbon atoms that don't have their bonds occupied. (not sure if that's the right terminology)
« Last Edit: February 12, 2013, 08:50:17 pm by Bad Student »
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pi

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Re: Chemistry 3/4 2013 Thread
« Reply #430 on: February 12, 2013, 08:48:10 pm »
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Bad Student's working looks fine to me. Whether they wanted people to simplify 0.45 as 0.5 or keep it as 5/11 is another matter. Personally I'd have Machi's answer.

Quote from: Machan on February 12, 2013, 08:43:47 pm
I got C9H10, did exactly what bad student did except multiple mole of h20 by 2.

Why did you do that btw? :)

Because each water molecule has 2 hydrogen atoms and hence you must multiply it by two to get the n(H) :)
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Daenerys Targaryen

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Re: Chemistry 3/4 2013 Thread
« Reply #431 on: February 12, 2013, 08:55:15 pm »
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It would have to be because isn't a alkane, alkene, alkyne. Or can it be a hydrocarbon still despite those three categories?
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teletubbies_95

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Re: Chemistry 3/4 2013 Thread
« Reply #432 on: February 12, 2013, 08:57:42 pm »
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After much confusion, I got the same answer as BadStudent! Is that right?
It cant be C9H10 or C5H11, as it doesnt match the general formulas for alkane, alkene and alkynes ! :)

Btw. Great question! :)
« Last Edit: February 12, 2013, 08:59:49 pm by teletubbies_95 »
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Mr Keshy

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Re: Chemistry 3/4 2013 Thread
« Reply #433 on: February 12, 2013, 09:01:32 pm »
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Ahhh okay, dunno what I was thinking!
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Re: Chemistry 3/4 2013 Thread
« Reply #434 on: February 12, 2013, 09:02:19 pm »
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Quote from: HatersGonnaHate on February 12, 2013, 08:55:15 pm
It would have to be because isn't a alkane, alkene, alkyne. Or can it be a hydrocarbon still despite those three categories?

There are other hydrocarbons, C5H11 would probably have a positive charge on it iirc. It's quite ambiguous.

Quote from: teletubbies_95 on February 12, 2013, 08:57:42 pm
Btw. Great question! :)


In all respect, I actually disagree, it's a question with quite an ambiguous answer despite the working being fairly straightforward (in comparison to other harder stoich questions).
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