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Topic: significant figures  (Read 4044 times)

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Offline Moss

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significant figures
« on: September 21, 2009, 05:57:52 AM »
hey
N2H4 + O2 --> N2 + 2H2O

DETERMINE WHICH IS IN EXCESS AND BY HOW MANY GRAMS

oxygen is in excess.

find how many grams

n(N2H4) = 2.29/ ( 2*14.01 + 4*1.01)
=0.071..

m(O2)= 0.071.. *32
=2.2857..

3.14-2.2857.. =0.854g

but the answer says 0.853g... this is really irritating me

please help
thanks
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Offline Borek

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Re: significant figures
« Reply #1 on: September 21, 2009, 06:16:25 AM »
State clearly what was the question, nobody is going to reverse engineer your answer to guess what was the original data.
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Offline Moss

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Re: significant figures
« Reply #2 on: September 21, 2009, 06:22:30 AM »
hydrazine is used in rocket fuel. it reacts with oxygen as follows:

N2H4 + O2 --> N2 + 2H2O

in a particular rocket engine,2.29g of hydrazine and 3.14g of oxygen are available for reaction.
DETERMINE WHICH IS IN EXCESS AND BY HOW MANY GRAMS.
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Offline kimyaa2

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Re: significant figures
« Reply #3 on: September 21, 2009, 07:07:52 AM »
the answere is so close to what you get..not a big deal..maybe there are some sig fig problems from the begining ..
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Offline Borek

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Re: significant figures
« Reply #4 on: September 21, 2009, 07:25:04 AM »
Most likely they used slightly different molar mass of hydrazine - your is 32.06, exact one is 32.0452.

But in this case giving answer with accuracy better than 0.85g is absurd.
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