We’re going to solve two different problems on this page. The first is relatively straight-forward, the second is the same sort of problem, but has an added issue that we’ll need to address.
A simple Problem
Let’s start by solving this problem:
It is tempting to think that this reaction must run backwards, since no reactant is present, but this is a solubility problem. The reactant is a solid, is not included in the math and therefore is NOT relevant.
What we actually need to do is to figure out what the question actually is. “Will a precipitate form? means “will a solid appear in the container?” For that to happen, the ions in solution need to stick together and form the solid compound. In other words: ?
And that is simple math.
> or = or \lt ? ?
Since , the reaction will run to the left and the answer is YES (a precipitate will form).
There are several things we need to think about before we can start the problem:A solution is made that is 0.0035 Mand 0.070 M . Will a precipitate form? The = .
-
Since we are given the
of then the relevant reaction must be the dissolving of even if that seems to come from out of nowhere. -
All nitrates are soluble (check your solubility table). That means that we don’t need to care about the
ions, on the ions, which have a concentration of 0.0035 M. -
All sodium compounds are soluble. So, like the nitrates, we can ignore the
ions and the = 0.070 M.
“Will a precipitate form?” = “Does the reaction run LEFT?”
That question, of course, is really asking: Is A More Complex Problem
Now, let's try a more complex problem:
So, in this case, the answer is NO (a precipitate will not form).