Ka and Kb Formula

[TiffanyBrownfield 2I]

So when you're given Ka it says the formula is [H+][A-]/[HA]. In the video I watched it said you can simply write it as just x^2/[molarity - x] since [H+] and [A-] are equal. Is this statement always true?

[Charmaine Ng 2D]

I'm not completely sure, so it'd be great if someone could fact check me!:
We've mostly been working with monoprotic acids, so this holds true for most of the problems we've done. However, note that it depends on the chemical equation's coefficients. If, for example, two moles of A- are gained from each mole of HA lost, then A- would have -2x, which would make [H+] and [A-] different. If it's monoprotic like the problems we've been doing so far, you don't have to worry about this!

[Bhuvan Kommineni 3L]

This is true for monoprotic acids.

[Jose Miguel Conste 3H]

I think this is honestly true, but I would just always write [H+][A-], so then it sticks that you're multiplying the conjugate base and prevent any problems

[Kandyce Lance 3E]

What key words should we look for in order to determine if we should be using Ka and Kb? This concept caused me a few issues with the homework

[Sarah Salam 1J]

What key words should we look for in order to determine if we should be using Ka and Kb? This concept caused me a few issues with the homework

In the homework, you'd need to use Ka when solving for a weak acid, and Kb when solving for weak bases. You solve for one by dividing 1x10^-14 by the other. The processes for using them are similar.

[Kaiya_PT_1H]

Yeah I think this is true for monoprotic acids, which is mostly what we work with in class!

[Mariah Disc 2C]

This will be true with the problems that we are focusing on in class!

[Adrienne Chan 1G]

This seems true for monoprotic acids!

[Dane_Beasley_1E]

That is true for all monoprotic acids.

[Geethika Janga 1L]

I'm pretty sure this holds true for most monoprotic acids.

[joshtully]

This is true for monoprotic acids.

[Sable Summerfield]

How do we know when we need to convert Kb to Ka or vice versa?

[Sam Wentzel 1F 14B]

This statement is ALWAYS true of weak monoprotic acids / bases but you can make assumptions about the x value on the bottom of the expression if the KA is 10^-3 or less, such that x on the bottom roughly = 0, but x on the top STILL = x.

[Queena Chu 3E]

Yep, I'm pretty sure its true for monoprotic acids.

[Susan Chamling 1F]

Hi, I believe this applies to most monoprotic acids.