July 03, 2020, 11:45:52 AM
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Topic: A serious chemistry problem for a bad chemistry student.  (Read 320 times)

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Offline gryva

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A serious chemistry problem for a bad chemistry student.
« on: June 10, 2020, 12:20:01 PM »
How to calculate the mass of SiO2 to get 500 kg of SiC with 65% of efficiency?
The answer is m(SiO2)=1150kg or 1.15 tons.
I think the equation needed for solving is SiO2+3C --> SiC+2CO
I need solving steps cause it seems my method doesn't work and I need it fast!
Thanks in advance fellow chemist!


Online chenbeier

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Re: A serious chemistry problem for a bad chemistry student.
« Reply #1 on: June 10, 2020, 01:33:27 PM »
Convert the mass to mole for SiC and convert back to the mass of SiO2.Then calculate the yield with 65%.

But show you own ideas.

Offline gryva

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Re: A serious chemistry problem for a bad chemistry student.
« Reply #2 on: June 10, 2020, 01:53:24 PM »
I did that, our teacher is very strict with the solving steps, but I think this will be fine.
Thank you, friend!

Offline AWK

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Re: A serious chemistry problem for a bad chemistry student.
« Reply #3 on: June 10, 2020, 02:03:39 PM »
1153 kg (exact masses of elements), 1154 kg (masses of elements rounded to whole numbers), so the answer should be 1.2 t, because 65% has 2 significant digits.
AWK

Offline MNIO

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Re: A serious chemistry problem for a bad chemistry student.
« Reply #4 on: June 10, 2020, 06:46:52 PM »
general steps for all stoichiometry problems
.. (1) write a balanced equation
.. (2) convert everything given to moles
.. (3) determine limiting reagent
.. (4) convert moles limiting reagent to moles product
.. (5) convert moles product to mass product.. this is theoretical yield
.. (6) % yield = actual mass recovered / theoretical yield * 100%

********
in your case, you're working backwards after step 1
.. (1) balanced reaction equation is.... what?
.. (6) actual mass SiC recovered = 500kg... % yield = 65%
.. .. . .----> theoretical yield SiC = __kg
.. (5) __ theoretical kg SiC = __ theoretical moles SiC
.. (4) __ theoretical moles SiC = __ theoretical moles SiO2
.. (3) what's the LR?
.. (2) moles SiO2 --> mass SiO2

and if you've been practicing that dimenisonal analysis you've been studying lately, you can do this all in 1 equation with 4 unit factors. 

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