How to assume X is too small

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Natalie LeRaybaud 1G
Posts: 54
Joined: Thu Jul 13, 2017 3:00 am

How to assume X is too small

Postby Natalie LeRaybaud 1G » Wed Dec 06, 2017 3:41 pm

Is there any way to assume X to be too small without calculating the actual value of X and using the 5% rule?

Courtney Cheney 3E
Posts: 19
Joined: Fri Sep 29, 2017 7:07 am

Re: How to assume X is too small

Postby Courtney Cheney 3E » Wed Dec 06, 2017 3:49 pm

I don't think so. My TA went over this today in discussion and said that when doing concentration calculations you're almost always going to assume X is too small and then check with the 5% rule. However, he did mention that if the concentration given is rather large (in the example in class it was 0.510 M CH3NH3+) then it is very unlikely that the X value will be large enough to make a difference.

Catherine Yang 3G
Posts: 24
Joined: Fri Sep 29, 2017 7:06 am
Been upvoted: 2 times

Re: How to assume X is too small

Postby Catherine Yang 3G » Wed Dec 06, 2017 3:54 pm

I think Dr. Lavelle mentioned that if K is less than 10^-4, then it can generally be assumed that X will be small enough to ignore, but we should definitely still check to make sure at the end.

Yifei Wang 3G
Posts: 19
Joined: Fri Sep 29, 2017 7:07 am

Re: How to assume X is too small

Postby Yifei Wang 3G » Wed Dec 06, 2017 3:56 pm

Normally in a reaction with extremely small K, we can apply the 5% rule, but make sure that the answer is less than 5% of the original concentration


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