- #1

JeweliaHeart

- 68

- 0

## Homework Statement

The molar solubility of magnesium fluoride, MgF

_{2}is 1 x 10

^{-3}in pure water. What is the Ksp for MgF

_{2}?

a)4 x 10

^{-3}

b)4 x 10

^{-6}

**c)4 x 10**

^{-9}d)2 x 10

^{-3}

e)1 x 10

^{-3}

My book says the correct answer is C in bold.

## Homework Equations

Ksp= [Mg2+][F-][F-]

## The Attempt at a Solution

Ksp= [Mg2+][F-][F-]=[1 x 10

^{-3}][1 x 10

^{-3}][1 x 10

^{-3}]=

**1 x 10**

^{-9}I think this should be the correct answer. For some reason the book multiplies by four. It says:

"The relationship between the solubility product constant and molar solubility for a compound that produces 3 moles of ions for every mole of solid dissolved is as follows:

Ksp=4x

^{3}= 4(1 x 10

^{-3})

^{3}= 4 x 10

^{-9}"

I don't understand why to multiply by four.