## Percent Ionization

Matt Sanruk 2H
Posts: 131
Joined: Wed Sep 18, 2019 12:21 am

### Percent Ionization

So as long as the percent Ionization is less than 5%, we don't have to do the quadratic equation right?

claudia_1h
Posts: 111
Joined: Fri Aug 09, 2019 12:16 am

### Re: Percent Ionization

Yes, because the change to the initial concentration of the acid or base will be essentially zero. But usually the percent ionization doesn't come first, and is a step to confirm that approximating was okay (which you would do based on the value of K being <10^-3).

Katie Kyan 2K
Posts: 106
Joined: Fri Aug 09, 2019 12:16 am
Been upvoted: 1 time

### Re: Percent Ionization

Yes as long as the percent ionization is less than 5% of the initial concentration then the approximation is okay. If the equilibrium constant is less than 10^-3 then you do not have to use the quadratic equation and to check, you would calculate the percent ionization as confirmation.

Matt Sanruk 2H
Posts: 131
Joined: Wed Sep 18, 2019 12:21 am

### Re: Percent Ionization

Oh ok this makes it a lot easier than the quadratic equation

Sanjana K - 2F
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### Re: Percent Ionization

If you don't use the quadratic equation, you still want to justify your reason for ignoring the "-x" terms in your equilibrium by saying that since x is less than 5% of the initial concentration, its change is negligible.

Jialun Chen 4F
Posts: 108
Joined: Sat Sep 07, 2019 12:16 am

### Re: Percent Ionization

That is correct! And I believe that in homework problems the % ionization is under 5% excluding certain outliers.

EthanPham_1G
Posts: 104
Joined: Sat Jul 20, 2019 12:17 am

### Re: Percent Ionization

If the Ka or Kb is less than 10^-3 then you can approximate x and you don't have to use the quadratic equation.
If the percent ionization is less than 5% then your approximation is correct.

Bryan Chen 1H
Posts: 58
Joined: Mon Jun 17, 2019 7:24 am

### Re: Percent Ionization

yea, and then afterwards do the x value over initial concentration just to double check it is under 5%

Matt Sanruk 2H
Posts: 131
Joined: Wed Sep 18, 2019 12:21 am

### Re: Percent Ionization

Cool, and even if the given concentration and ka/kb are both 10^-4 or lower it will still be the case right?

Juana Abana 1G
Posts: 100
Joined: Wed Sep 18, 2019 12:15 am

### Re: Percent Ionization

Yes, as long as the percent Ionization is less than 5% we don't have to do the quadratic equation.

Bryan Chen 1H
Posts: 58
Joined: Mon Jun 17, 2019 7:24 am

### Re: Percent Ionization

Yea I always check to see if K is small but if its around like 10 to -3 or -4, you can do the approximation but make sure to check if x is less than 5% of the initial concentration

Matt Sanruk 2H
Posts: 131
Joined: Wed Sep 18, 2019 12:21 am

### Re: Percent Ionization

But there will always be a problem where the %ionization is not under 5 % of course...