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April 18, 2015

April 18, 2015

Posted by **Samuel** on Friday, October 15, 2010 at 4:55pm.

i am trying to use v1/n1=v2/n2 but i am stuck, can u help? thank you

- Chemistry Help -
**DrBob222**, Friday, October 15, 2010 at 5:12pmWill something like this work?

# breaths to blow 3.0 L balloon = 3 breaths x (3.0 L/1.2 L) = 7.5 breaths [or you can use the dimensional analysis method which will be 3.0

L x (3 breaths/1.2 L) =7.5 breaths.

Each breath has 0.06 moles; therefore,

0.060 moles/breath x 7.5 breaths = ?? moles

- Chemistry Help -
**Samuel**, Friday, October 15, 2010 at 5:48pmusing your method i got 0.45moles,is that correct?

- Chemistry Help -
**DrBob222**, Friday, October 15, 2010 at 6:06pmThat was my answer, also. Check my thinking on the problem.

- Chemistry Help -
**Amy**, Friday, October 15, 2010 at 6:11pmits saying that i am wrong, im stuck

- Chemistry Help -
**Amy**, Friday, October 15, 2010 at 6:37pmhello?

- Chemistry Help -
**DrBob222**, Friday, October 15, 2010 at 9:38pmAfter re-reading the problem very carefully, I'm sticking with my answer. By the way, your v1/n1 = v2/n2 is exactly the same.

1.2/0.18 = 3.0/n2

n2 = 3.0 x (0.18/1.2) = 0.45

I think the problem with your answer is that the number 0.06 moles has only one significant figures in it; therefore, the answer must be rounded to one s.f. So the answer must be rounded from 0.45 moles to either 0.4 or 0.5 depending upon how your teacher has told you to round number when they end in 5. The rule I follow is to "round to the even number"; therefore, I would round to 0.4 but not everyone follows that rule. Let me know if this does or does not take care of the problem. As an interesting aside, note that if we round at the end, I would round to 0.4 BUT if I rounded at the 7.5 mark, I would round that to 8 and 8 x 0.06 = 0.48 which of course rounds to 0.5

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