Page 1 of 1

### 5% Rule

Posted: Sat Mar 14, 2020 5:37 pm
Can someone elaborate what the 5% rule is?

### Re: 5% Rule

Posted: Sat Mar 14, 2020 5:38 pm
when using the approximation (removing x when you are subtracting/adding it to something) you must check to make sure that x is less than 5% of the reactant that it is formed from (x will likely be H or OH- so you would use the acid or base)

### Re: 5% Rule

Posted: Sat Mar 14, 2020 5:40 pm
So if it meets the rule, do we just ignore the value?

### Re: 5% Rule

Posted: Sat Mar 14, 2020 5:41 pm
You put the concentration you got from approximated the concentrations in the equilibrium values (from an ICE table) over the original concentration that's given and if it is less than 5% the approximation is sound, then if not then you have to use the quadratic formula to find the values.

### Re: 5% Rule

Posted: Sat Mar 14, 2020 5:43 pm
You also know that you can use the approximation if your equilibrium constant, K, is small enough.

### Re: 5% Rule

Posted: Sat Mar 14, 2020 5:58 pm
The five percent rule is used in ICE tables. If the x value you get is 5% or less than the initial then you can ignore it. I believe that if the K is 10^-3 or less you can usually make this assumption.

### Re: 5% Rule

Posted: Sat Mar 14, 2020 7:31 pm
Its for simplifying ICE calculations. If the end result is less than 5%, than the approximation is accurate.