approximation

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Ghadir Seder 1G
Posts: 134
Joined: Sat Sep 14, 2019 12:17 am

approximation

Postby Ghadir Seder 1G » Wed Jan 22, 2020 2:32 pm

can someone explain to me the rules of when we can approximate when K is smaller than 10^-3?

AArmellini_1I
Posts: 107
Joined: Fri Aug 09, 2019 12:15 am

Re: approximation

Postby AArmellini_1I » Wed Jan 22, 2020 2:41 pm

Basically if K is less than 10^3, meaning that the acid/base barely disassociates, then we can assume that the dissociation affects the initial condition of your acid/base so little that it's insignificant. This means that when calculating your x, or the change in concentration, instead of have your denominator being [inital] - x, you can just leave it as [initial] since the concentration does not change significantly.

Ghadir Seder 1G
Posts: 134
Joined: Sat Sep 14, 2019 12:17 am

Re: approximation

Postby Ghadir Seder 1G » Wed Jan 22, 2020 5:33 pm

is the cutoff 10^-3? or 10^3?

bellaha4F
Posts: 104
Joined: Wed Sep 18, 2019 12:20 am

Re: approximation

Postby bellaha4F » Wed Jan 22, 2020 6:03 pm

10^-3

Vivianvelazquez_1J
Posts: 109
Joined: Thu Jul 11, 2019 12:17 am
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Re: approximation

Postby Vivianvelazquez_1J » Wed Jan 22, 2020 6:34 pm

Ghadir Seder 1G wrote:is the cutoff 10^-3? or 10^3?

10^-3 is the cutoff.

Julie_Reyes1B
Posts: 105
Joined: Sat Jul 20, 2019 12:16 am

Re: approximation

Postby Julie_Reyes1B » Wed Jan 22, 2020 6:52 pm

It's also important to double check that the x value is in fact less than 5% of the initial concentration or the approximation is invalid. I always do that at the end of every problem in which I approximate, especially when the K value is only slightly smaller than 10-3


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