Question 31

[h99h20baby]

In this case, the Ka of H2S is relatively small (approx. 10- and thus H2S is a weak acid. Since H2S is a weak acid, very, very little H and HS- would be formed, and, even a smaller amount of H and S2- from the even weaker acid HS-. In other words, only a minute quantity of S2- would come from H2S, and despite such a low quantity, it is enough S2- to precipitate Pb, Cu and Ag. Thus the Ksp that is given by [X2 ][S2-] must be a very very (!) small quantity.

how do you know the minute quantity of S2- is enough to precipitate out Pb, Cu, and AG? I know the bottom of the chart has them as insoluble. I am confused. thank you
Regards

[admin]

Carefully examine Figure 1: it begins with a neutral solution of cations, H2S is added and then one of the boxes shows that as a result of H2S being added, 5 metal sulfides are precipitated: Cu, Pb, Ni, Ag, Zn.

PS. Even if you had not looked at the Fig (which I'm not recommending!), with experience of doing problems, you will see that Ksp values are always very low, always. In fact, seeing 10 to the exponent of -20 to -60 is quite common.

[StoneColdPS14]

Answer Choice D is also true. so if you picked it don't feel bad!

[admin]

Bump.