# What is the molar solubility of magnesium fluoride in a solution that is #"0.1 M"# sodium fluoride?

##### 2 Answers

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

**I**.......

**C**.....

**E**......

According to the definition of the solubility product constant, you'll get

Since

The molar solubility =

You should be given a value for the solubility product

From

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

We'll give

Now put the values into

From which :