What is the molar solubility of magnesium fluoride in a solution that is #"0.1 M"# sodium fluoride?
In your case, the molar solubility of magnesium fluoride will be
You need the value of the solubility product constant,
If this is not the value given to you, just replace it in the calculations with whatever value you have.
So, the equilibrium equation for the dissociation of magnesium fluoride is
The key to this problem is the fact that, even before adding the magnesium fluoride, your solution contains fluoride anions,
Notice that 1 mole of sodium fluoride produces 1 mole of fluoride ions in solution; this means that the initial concentration of fluoride ions will be
Construct an ICE table for equation
According to the definition of the solubility product constant, you'll get
The molar solubility =
You should be given a value for the solubility product
This will also happen if we try to dissolve the salt in a solution which contains an ion which is common, in the case
This is known as "The Common Ion Effect".
The molar solubility of the salt is also equal to
To make things simple we can assume that any
Now put the values into
From which :