5%

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Gabriel Ordonez 2K
Posts: 113
Joined: Sat Jul 20, 2019 12:15 am

5%

Postby Gabriel Ordonez 2K » Sun Jan 19, 2020 7:36 pm

What is the 5% deal that Lavelle talks about in equilibrium oriented questions. How do we get to that point?

Christine Honda 2I
Posts: 116
Joined: Sat Sep 14, 2019 12:17 am

Re: 5%

Postby Christine Honda 2I » Sun Jan 19, 2020 7:42 pm

The 5% rule applies to when you use the ICE table. If K is less than 10^-3, then you can assume that X is so small that it will not make a difference. For example if you have K=X^2/(0.3-X), then you can change it to X^2/0.3 because the X in the denominator becomes negligible. The 5% rule is if you find that X is less than 5% of the initial concentration, then the approximation is valid.

Chris Charton 1B
Posts: 69
Joined: Mon Jun 17, 2019 7:23 am

Re: 5%

Postby Chris Charton 1B » Sun Jan 19, 2020 7:45 pm

If you approximate the result with a small Ka (<10^-3) and end up with a change value of <5% of initial value then your approximation is valid. Otherwise you need to do the full quadratic calculation.

RobertXu_2J
Posts: 104
Joined: Fri Aug 30, 2019 12:17 am

Re: 5%

Postby RobertXu_2J » Sun Jan 19, 2020 8:02 pm

When using approximations for ICE tables, if you find that X is less than 5% of the initial concentration, then the approximation is valid.

Shimei_2F
Posts: 100
Joined: Fri Aug 09, 2019 12:17 am

Re: 5%

Postby Shimei_2F » Sun Jan 19, 2020 8:06 pm

You're allowed to approximate X while doing ICE tables if the K constant is less than 1.0x10^-3. If the answer is less than 5% of the initial molarity, then the approximation is okay.


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