When to approximate

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Jada Brown 2H
Posts: 100
Joined: Sat Aug 17, 2019 12:15 am

When to approximate

Postby Jada Brown 2H » Tue Jan 14, 2020 8:52 pm

I know that when your ICE equation ends up cubed, you can usually use the approximation rules to solve. Can you do this for squared equations as well as long as the k value is small enough?

Ariel Davydov 1C
Posts: 110
Joined: Thu Jul 11, 2019 12:16 am
Been upvoted: 1 time

Re: When to approximate

Postby Ariel Davydov 1C » Tue Jan 14, 2020 8:58 pm

According to Lavelle’s slides, we can only do this if the equation is cubed AND the K value is <<< 10^-3.

Daniel Honeychurch1C
Posts: 109
Joined: Thu Jul 11, 2019 12:15 am

Re: When to approximate

Postby Daniel Honeychurch1C » Tue Jan 14, 2020 9:02 pm

According to the textbook for question 5I.29, which has a squared function, you can assume x is too small to affect the calculations when K is really small.

Daria Azizad 1K
Posts: 116
Joined: Thu Jul 25, 2019 12:15 am

Re: When to approximate

Postby Daria Azizad 1K » Tue Jan 14, 2020 10:11 pm

We should be able to approximate in binomials as well. If you approximate it or solve it fully out, you get the same value.

andrewcj 2C
Posts: 102
Joined: Thu Jul 11, 2019 12:17 am

Re: When to approximate

Postby andrewcj 2C » Tue Jan 14, 2020 10:54 pm

I'm not sure if this rule applies in this class, but my TA gave out a worksheet today in which we were supposed to approximate that subtracting X from a concentration doesn't change the concentration. The worksheet asks for you to check if the concentration of the product, or X, was less than 5% of the original concentration of the reactant, and I think this works as a sanity check. If you finish the problem and find out that the product formed was less than 5% of the original concentration of the reactant, then it seems reasonable that you assumed subtracting X did not significantly change the concentration of the reactants.

AlyshaP_2B
Posts: 112
Joined: Wed Sep 18, 2019 12:19 am

Re: When to approximate

Postby AlyshaP_2B » Wed Jan 15, 2020 9:02 am

If the percent protonation is less than 5%, you can assume that your approximation was appropriate.


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