### 5% Rule

Posted:

**Wed Jan 23, 2019 9:11 am**Does the 5% Rule for approximation only apply to acid/base reactions in water? Can we use the approximation technique for small K values for equilibrium problems not involving acid/base?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=49&t=40539

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Posted: **Wed Jan 23, 2019 9:11 am**

Does the 5% Rule for approximation only apply to acid/base reactions in water? Can we use the approximation technique for small K values for equilibrium problems not involving acid/base?

Posted: **Wed Jan 23, 2019 11:14 am**

The 5% approximation technique can be used for any K calculation, provided

K < 10-3 — Very little product formed, R-x = R

K > 103 — Very little reactant remaining, P+x = P

K < 10-3 — Very little product formed, R-x = R

K > 103 — Very little reactant remaining, P+x = P

Posted: **Wed Jan 23, 2019 8:19 pm**

The 5% ionization approximation can be applied to any K calculation as long as K is less that 10^-3

Posted: **Wed Jan 23, 2019 9:10 pm**

the 5 percent rule can be used in any calculation of K

Posted: **Wed Jan 23, 2019 10:54 pm**

But if you do disregard x make sure to double check that it is under 5% because if not the solution is incorrect.

Posted: **Thu Jan 24, 2019 1:41 pm**

you can use the 5% rule for a K value that is less than 10^-3 for acids and bases or equilibrium concentrations and pressures.