ignoring x

marcus lin 1E
Posts: 54
Joined: Fri Sep 28, 2018 12:28 am

ignoring x

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

BenJohnson1H
Posts: 68
Joined: Fri Sep 28, 2018 12:17 am

Re: ignoring x

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%

Hilda Sauceda 3C
Posts: 76
Joined: Fri Sep 28, 2018 12:24 am

Re: ignoring x

we ignore it when its = to or less than 10^3 because its a really small number that wont make a big difference to the answer

Olivia Young 1A
Posts: 60
Joined: Fri Sep 28, 2018 12:24 am

Re: ignoring x

You only ignore X when it is being added or subtracted from a number, because X is so small that it barely makes any difference to the resulting value. This occurs when K is less than 10^-3. If X is by itself or being squared on the numerator of a fraction, don't assume X is 0 and instead continue solving for that X value.

Lauren Ho 2E
Posts: 70
Joined: Tue Oct 09, 2018 12:16 am

Re: ignoring x

Do we need to write anything to indicate or explain why we have ignored x? Or can we just do it without indication if our problem passes the 5% test?

riddhiduggal
Posts: 30
Joined: Fri Sep 28, 2018 12:21 am

Re: ignoring x

You can ignore x when it is less than 10^-3 which is very small and insubstantial

Anand Narayan 1G
Posts: 61
Joined: Fri Sep 28, 2018 12:15 am

Re: ignoring x

You should ignore it when k is equal to or less than 10^-3

Stevin1H
Posts: 89
Joined: Fri Sep 28, 2018 12:17 am

Re: ignoring x

We can only ignore x in an ice table when the equilibrium constant, K, is less than 10^-4. Also, we are not necessarily saying x is 0. We can neglect the x because the value of x is so small that it makes very minimal difference when subtracting from the initial concentration. For example, if the initial concentration is 0.5 and x is 1x10^-7, subtracting 0.5 is essentially just 0.5 since the x is very small.

Phan Tran 1K
Posts: 29
Joined: Fri Sep 28, 2018 12:19 am

Re: ignoring x

You can also check for this by finding the percent protonization by taking the concentration you get and dividing it bby the original concentration of your acid/base. If it's less than 5% then treating x as being so small that it is insignificant is valid.

Ethan Breaux 2F
Posts: 63
Joined: Sat Sep 29, 2018 12:16 am

Re: ignoring x

everything above^^^ and you can check the 5% rule by taking the value you plug into the -log for pH and dividing it by the original starting concentration of whatever weak acid was used in the problem (usually a given) then you multiply it by 100%

Maria Solis Disc 1G
Posts: 63
Joined: Fri Sep 28, 2018 12:27 am
Been upvoted: 2 times

Re: ignoring x

I was also told that you HAVE TO check the 5% rule, you cant just choose if you want to check. It's better to be safe than sorry.

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