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Topic: Mass Calc  (Read 4923 times)

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Offline FouRRaW

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Mass Calc
« on: November 23, 2006, 09:07:05 PM »
with the equation 4Na + O2 ---> 2Na2O
If there are 18.0 g of Na, how many grams of O2 are required for the reaction to take place?

My attempt... first figure out moles of Na                (18.0g) x (1mol Na/22.990g)          =0.7829 mol Na
then 4Na:1O2     so divide (0.7829mol Na/4) =     0.1957mol O2

then mass O2 = mm/mol which would be...  32g/0.1957mol=163.52g     which is wrong??

what did i do wrong and how do i fix it?
   
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Offline Mitch

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Re: Mass Calc
« Reply #1 on: November 23, 2006, 09:32:38 PM »
32g/0.1957mol <~~~~ Those units don't cancel to give you grams. Do you know dimensional analysis?
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Offline FouRRaW

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Re: Mass Calc
« Reply #2 on: November 23, 2006, 09:35:47 PM »
no i don't know dimensional analysis
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Offline FouRRaW

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Re: Mass Calc
« Reply #3 on: November 23, 2006, 09:37:02 PM »
sorry for that part i  meant (32 g/mol)/0.1957mol)
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Offline FouRRaW

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Re: Mass Calc
« Reply #4 on: November 23, 2006, 09:37:37 PM »
oops taht still don't work, hehe
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Offline Borek

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Re: Mass Calc
« Reply #5 on: November 24, 2006, 03:52:45 AM »
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Offline mz4000

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Re: Mass Calc
« Reply #6 on: November 30, 2006, 11:48:54 AM »
Alright first you take the number of grams of Sodium then divide that by sodium's atomic mass.  then multiply by the ratio of moles of Oxygen to moles of Sodium.  Which in this case is 1/4.  Then to convert to grams multiply it by the atomic mass of O2 which is like 32.  You should get your answer from there.
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