Percent Ionization

[Matt Sanruk 2H]

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

[claudia_1h]

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]

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]

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

[Sanjana K - 2F]

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]

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

[EthanPham_1G]

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]

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

[Matt Sanruk 2H]

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]

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

[Bryan Chen 1H]

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]

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