### X Value

Posted:

**Sat Jan 19, 2019 9:14 pm**I know that 10^-5 or lower is when we can disregard the x but if something is 10^-4, can we still disregard and just check that the x value divided by the initial concentration is less than 5%

Created by Dr. Laurence Lavelle

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

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=49&t=40258

Page **1** of **1**

Posted: **Sat Jan 19, 2019 9:14 pm**

I know that 10^-5 or lower is when we can disregard the x but if something is 10^-4, can we still disregard and just check that the x value divided by the initial concentration is less than 5%

Posted: **Sat Jan 19, 2019 9:22 pm**

I believe this rule is actually anything below 10 to the -3 not -5 so if you had a number to the -4 you should be alright to leave it out. I am not 100% sure that is correct but the 5% rule at the end will always let you know if it was okay to round it a bit.

Posted: **Sat Jan 19, 2019 11:29 pm**

yeah. if your estimate is <5% of the original value, then the estimate is ok to use. and the range is 10^-3 to 10^3

Posted: **Sun Jan 20, 2019 12:44 am**

The rule is that if the value of either Ka or Kb is less that 10^-3 so it is fine to disregard x for a value of 10^-4.