Approximation

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Selena Yu 1H
Posts: 83
Joined: Fri Aug 09, 2019 12:16 am

Approximation

Postby Selena Yu 1H » Thu Jan 16, 2020 12:37 am

Why is it that if X is less than 5% of initial then approximation is okay? Like why is the cut off 5%?

Ronak Naik
Posts: 83
Joined: Sat Jul 20, 2019 12:15 am

Re: Approximation

Postby Ronak Naik » Thu Jan 16, 2020 12:41 am

I think there is no official reason why it is 5%; however, the approximation check is used to make sure that X is such a small number that it allows to consider it insignificant when add or subtracting to another number.

Sanjana K - 2F
Posts: 86
Joined: Sat Sep 07, 2019 12:17 am
Been upvoted: 1 time

Re: Approximation

Postby Sanjana K - 2F » Thu Jan 16, 2020 9:21 am

In class, he also said that if your Ka is less than 10^(-3), then you can generally approximate by ignoring the "-x" term but you might want to justify it on the test by explaining that since x is less than 5% of the initial concentration, it's considered a negligible difference so it can be "ignored."

Alondra
Posts: 31
Joined: Tue Feb 26, 2019 12:15 am

Re: Approximation

Postby Alondra » Sun Jan 19, 2020 5:57 pm

I believe this has to do with the value being so small that it barely even causes a minimal change on a bigger initial concentration.

J Medina 2I
Posts: 78
Joined: Wed Sep 25, 2019 12:17 am

Re: Approximation

Postby J Medina 2I » Sun Jan 19, 2020 6:43 pm

Does it have to do with using significant figures? Like when we round our answer to a significant figure, the difference in our answer that a -X would have provided does not even make a difference in our final rounded answer?

TimVintsDis4L
Posts: 81
Joined: Sat Aug 17, 2019 12:17 am

Re: Approximation

Postby TimVintsDis4L » Sun Jan 19, 2020 6:50 pm

I doubt there's any science behind it being 5%. Scientists are lazy so they just choose a good number to go by and stick with that. The 5% is just something for us to follow as to whether or not to use the quadratic formula.

Charysa Santos 4G
Posts: 86
Joined: Wed Sep 18, 2019 12:21 am

Re: Approximation

Postby Charysa Santos 4G » Sun Jan 19, 2020 7:16 pm

It's just a general rule to check whether or not your approximation is valid because the amount (X) should be small enough that it wouldn't profoundly impact your equilibrium expression.


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