Another answer to check
![Grin ;D](https://www.chemicalforums.com/Smileys/classic/grin.gif)
Here's the exercise:
- • -
Of a diprotic acid H
2A both K
1 and K
2 are known (the equilibrium constants for the first and the second dissociation). A salt soluble in water, MHA, of a monovalent metal M dissociates completely according to the following equation:
MHA→M
++HA
-Take a diluted solution of this salt:
a) Demonstrate that K
1K
2>K
w it's necessary (pay attention to these words) for pH<7 (the solution is acidic).
[
![](https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fwww.forkosh.dreamhost.com%2Fmimetex.cgi%3F%7B+pH%26lt%3B7+%5CRightarrow+K_1+K_2%26gt%3BK_w+%7D&hash=9c74824fae21ed2961e5ab4771ddc2d98ab11141)
]
b)Is this condition sufficient too?
[
![](https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fwww.forkosh.dreamhost.com%2Fmimetex.cgi%3F%7B+K_1+K_2%26gt%3BK_w+%5CLeftarrow+pH+%7D&hash=4d18bc2c478c3ecf8d3cf33599366ea0270c956a)
]
- • -
These equations describe the hydrolysis and the dissociation of HA
-:
![](https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fwww.forkosh.dreamhost.com%2Fmimetex.cgi%3F%7B+%5Cbegin%7Barray%7D%7Bl%7D%3Cbr+%2F%3EHA%5E-%2BH_2O%3DH_2A%2BOH%5E-%5C%5C+%3Cbr+%2F%3EHA%5E-%2BH_2O%3DA%5E-%2BH_3+O%5E%2B%5C%5C+%3Cbr+%2F%3E%5Cend%7Barray%7D+%7D&hash=4a136235f5bf180ded67c7a8eb5bed5446e696ee)
a)
![](https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fwww.forkosh.dreamhost.com%2Fmimetex.cgi%3F%7B+%5Cbegin%7Barray%7D%7Bl%7D%3Cbr+%2F%3E%5Cfrac%7B%7BK_w+%7D%7D%7B%7BK_1%7D%7D%3D+%5Cfrac%7B%7B%5Cleft%5B+%7BH_2A%7D+%5Cright%5D%5Cleft%5B+%7BOH%5E-%7D+%5Cright%5D%7D%7D%7B%7B%5Cleft%5B+%7BHA%5E-%7D+%5Cright%5D%7D%7D+%5Csimeq+%5Cfrac%7B%7B%5Cleft%5B+%7BOH%5E-%7D+%5Cright%5D%5E2+%7D%7D%7B%7B%5Cleft%5B%7BHA%5E-%7D+%5Cright%5D%7D%7D%5C%5C+%3Cbr+%2F%3E%5Cleft%5B+%7BOH%5E-%7D+%5Cright%5D%3D+%5Csqrt+%7B%5Cleft%5B%7BHA%5E-%7D+%5Cright%5D+%5Ccdot+%5Cfrac%7B%7BK_w%7D%7D%7B%7BK_1%7D%7D%7D%5C%5C+%3Cbr+%2F%3E%5Cend%7Barray%7D+%7D&hash=7045c75e720aa8b4c78de0c888c30d5a9ba950ed)
![](https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fwww.forkosh.dreamhost.com%2Fmimetex.cgi%3F%7B+%5Cbegin%7Barray%7D%7Bl%7D%3Cbr+%2F%3EK_2%3D+%5Cfrac%7B%7B%5Cleft%5B%7BA%5E-%7D+%5Cright%5D%5Cleft%5B+%7BH_3O%5E%2B%7D+%5Cright%5D%7D%7D%7B%7B%5Cleft%5B%7BHA%5E-%7D+%5Cright%5D%7D%7D+%5Csimeq+%5Cfrac%7B%7B%5Cleft%5B%7BH_3+O%5E%2B%7D+%5Cright%5D%5E2+%7D%7D%7B%7B%5Cleft%5B+%7BHA%5E-%7D+%5Cright%5D%7D%7D%5C%5C+%3Cbr+%2F%3E%5Cleft%5B%7BH_3O%5E%2B%7D+%5Cright%5D%3D+%5Csqrt+%7B%5Cleft%5B%7BHA%5E-%7D+%5Cright%5D+%5Ccdot+K_2%7D%5C%5C+%3Cbr+%2F%3E%5Cend%7Barray%7D+%7D&hash=a9c512fc0ebe2fa5d1f53d0f6ab27f9ae56f1274)
![](https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fwww.forkosh.dreamhost.com%2Fmimetex.cgi%3F%7B+%5Cbegin%7Barray%7D%7Bl%7D%3Cbr+%2F%3E%5Cleft%5B%7BH_3+O%5E%2B%7D+%5Cright%5D%26gt%3B+%5Cleft%5B%7BOH%5E-%7D+%5Cright%5D%5C%5C+%3Cbr+%2F%3E%5Cleft%5B%7BHA%5E-%7D+%5Cright%5D+%5Ccdot+K_2%26gt%3B+%5Cleft%5B%7BHA%5E-%7D+%5Cright%5D+%5Ccdot+%5Cfrac%7B%7BK_w%7D%7D%7B%7BK_1%7D%7D%5C%5C+%3Cbr+%2F%3EK_1K_2%26gt%3BK_w%5C%5C+%3Cbr+%2F%3E%5Cend%7Barray%7D+%7D&hash=09d87358bf35299390f228be165fed7970b13488)
I suppose it's ok, but obviously if you find any mistake tell me ^^
b)
Here's the main problem: I'd say that yes, this condition is sufficient too... but my question is: to demonstrate this fact should I rewrite the whole thing starting from K
1K
2>K
w? Or do I have to find another way to reach the acidity condition? (but in fact up to now I haven't been able to find one)