Can you classify acids as strong or weak from their formulas alone?  [ENDORSED]

Acidity
Basicity
The Conjugate Seesaw

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Wesley_Rugen_1E
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Can you classify acids as strong or weak from their formulas alone?

Postby Wesley_Rugen_1E » Sat Nov 26, 2016 5:08 pm

Can you classify acids as strong or weak from their formulas alone?

Justin Folk 3I
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Re: Can you classify acids as strong or weak from their formulas alone?

Postby Justin Folk 3I » Sat Nov 26, 2016 6:01 pm

No, usually not. The only strong acids are the ones that are listed as "strong acids," and we know this because a Ka value doesn't exist-- everything dissociates so [HA] == 0, and Ka becomes undefined.

Theoretically, you could deduce based on electronegativity its ionic vs covalent character. But just memorize the strong acids.

Yamilex Velgara 2I
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Re: Can you classify acids as strong or weak from their formulas alone?

Postby Yamilex Velgara 2I » Sat Nov 26, 2016 6:41 pm

I'm not entirely sure, but for the purpose of this class, memorize the list of strong acids. All other acids will most likely be weak acids, according to my PLF.

Laine Gruver 3C
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Re: Can you classify acids as strong or weak from their formulas alone?

Postby Laine Gruver 3C » Sat Nov 26, 2016 7:39 pm

Does anybody know if the list of strong acids in the course reader is exhaustive?

Tycho_Meimban_2B
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Re: Can you classify acids as strong or weak from their formulas alone?

Postby Tycho_Meimban_2B » Sat Nov 26, 2016 8:16 pm

Better to memorize the list of all strong acids and bases. I would assume that if an acid or base is not strong, then it is weak.

divya_devineni_2E
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Re: Can you classify acids as strong or weak from their formulas alone?

Postby divya_devineni_2E » Sat Nov 26, 2016 8:26 pm

So does that mean for any acid or base that has a K value, we can disregard the subtracted "x" from the reactants when setting up the equilibrium formula?

Anna Makridis_L1
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Re: Can you classify acids as strong or weak from their formulas alone?

Postby Anna Makridis_L1 » Sun Nov 27, 2016 3:40 pm

Yes, I think you are correct in assuming that because the x value would be so small anyways that it doesn't matter if you subtract it. However it is important to remember that it is still greater than 0 because if it was 0 then your numerator wouldn't make sense either.

Chem_Mod
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Re: Can you classify acids as strong or weak from their formulas alone?  [ENDORSED]

Postby Chem_Mod » Sun Nov 27, 2016 8:14 pm

divya_devineni_1E wrote:So does that mean for any acid or base that has a K value, we can disregard the subtracted "x" from the reactants when setting up the equilibrium formula?


Only for K values that are less than 10-4 as I discussed in class.
Remember to check the % product formed and if it is less than 5% of the initial reactant concentration then approximation is acceptable.

If one has an acid or base with a K = 10-1 (for example) then X is unlikely to be less than 5%.

K will not be given for a strong acid and base. Look for this in a question if you don't recognize the acid or base as strong/weak.


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