Question

Above what Fe2+ concentration will Fe(OH)2 precipitate from a buffer solution that has a pH of 9.99? The Ksp of Fe(OH)2 is 4.87

Answer 1

Concept and reason

The concept used is to calculate the concentration of .

Fundamentals

The solubility product, is the equilibrium constant for a solid that is dissolved in a solution. It is the product of the concentration of the products raised to the power of their coefficients.

is the measure of hydrogen ion concentration. Lower the , higher is the hydrogen ion concentration and lower is the hydroxide ion concentration.

Higher the , lower is the hydrogen ion concentration and higher is the hydroxide ion concentration.

The hydrogen ion concentration is calculated as follows:

$[H]=10-PH1 $

The hydroxide ion concentration and are related as follows:

1.

The hydrogen ion concentration is as follows:

The hydroxide ion concentration is as follows:

The given salt is .

Its dissociation in water is as follows:

The expression for the solubility product is as follows:

Substitute the values of solubility product and the hydroxide ion concentration in the formula for solubility product and calculate the concentration of as follows:

Ans: Part 1

Therefore, the is .