### ignoring x

Posted:

**Mon Jan 21, 2019 7:25 pm**so for some of the ICE table calculations we ignore x and just pretend it's 0, when do we do that?

Created by Dr. Laurence Lavelle

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

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=50&t=40437

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Posted: **Mon Jan 21, 2019 7:25 pm**

so for some of the ICE table calculations we ignore x and just pretend it's 0, when do we do that?

Posted: **Mon Jan 21, 2019 7:30 pm**

When k is equal to or less than 10^3 you can omit any X that is being added or subtracted. To check, see if the dissociation of the acid/base is equal to or lower than 5%.

Posted: **Tue Jan 22, 2019 8:30 pm**

You can ignore x in the ice table when the K value is less than 10^-3 because it the percent ionization will be less than 5%.

Posted: **Tue Jan 22, 2019 8:52 pm**

You can ignore x in some instances because the amount that dissociates will be so little that it is insignificant to the overall decrease in the molarity. If the K value is extremely small, namely less than 10^-3, it means that reactants are favored in the reaction and so little of the reactants will be converted into products and therefore, the x value is so little and its subtraction is negligent.

Posted: **Wed Jan 23, 2019 4:25 pm**

Also, it is important to keep in mind that x is not actually 0 because if you plug in 0 for all x's it will be impossible to solve for x. However, it is useful in approximations to make the calculations more simple as the other replies have stated.

Posted: **Wed Jan 23, 2019 4:29 pm**

Keep in mind that x is only considered to be 0 when it is being added or subtracted to a number, not when it is alone and being multiplied

Posted: **Sun Jan 27, 2019 5:44 pm**

You can ignore x in an equilibrium equation when the percent deprotonation or protonation is less than 5%. This is because x will be negligible in the denominator related to the other initial value.

Hope this helps correct me if i'm wrong.

Hope this helps correct me if i'm wrong.

Posted: **Mon Feb 04, 2019 4:41 pm**

If the K value is less than 10^-3, you can ignore the x in the denominator if it is being added or subtracted to the initial concentration. This is because it'll make such a minute difference in the equilibrium concentration as a whole. Be careful that you don't just substitute all the x values with 0!

Posted: **Tue Feb 05, 2019 2:43 pm**

When k is equal to or less than 10^3.

Posted: **Sat Mar 02, 2019 7:05 pm**

you can ignore x when youre approximating. this is when your k value is less than or equal to 10^-3

Posted: **Sun Mar 03, 2019 10:02 pm**

You can ignore x when k is less than 1x10^-3

Posted: **Sun Mar 10, 2019 7:41 pm**

X is zero if follows 5% rule or if K is less than 10^-3. Therefore no need to use quadratic equation

Posted: **Mon Mar 11, 2019 10:43 am**

X can be ignored when k is less than 1x10^-3

Posted: **Mon Mar 11, 2019 10:45 am**

You can ignore x when approximating (when K<10^-3), but make sure to check your work after to make sure x is indeed less than or equal to 5% deprotonation!

Posted: **Fri Mar 15, 2019 1:12 pm**

A good way to check if your approximation was valid is to see if x is less than 5% of the initial concentrations

Posted: **Fri Mar 15, 2019 9:35 pm**

when K is less than 1*10^-3 but I think Dr. Lavelle said on the midterm that he wants use to always use the quadratic formula so I can only assume that applies to the final as well

Posted: **Sat Mar 16, 2019 11:09 pm**

We can ignore x when the 5% rule applies to it, which is when x is less than 5% of the initial concentration.