This video is about solubility and my question is about writing the Ksp, the solubility constant.

I understand that equilibrium constants are always written as K = [Products]/[Reactants]. And in general, we omit solids (s) and liquids (s) from the equilibrium formula.

On slide 2 (at 1:38) Brian states the importance of setting up the equations right. He states that the stoichiometric coefficient should be place inside the brackets and also as the exponent. So, given the example in the video,

*Solving for Molar Solubility using Ksp*, the dissociation equation is:

( x Mg3(PO4)2 (s) + H2O (l) <--> 3x Mg^2+ (aq) + 2x PO4^3- (aq) )

The Ksp should look like this:

Ksp = [3x Mg^2+]^3 * [2x PO4^3-]^2

And simplifying, the Ksp is:

Ksp = [3x]^3 * [2x]^2

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**Herein lies my confusion**

I looked at this Khan Academy video to get further clarification about Ksp. Mid video, the instructor uses an ICE table (5:51) to obtain the Ksp. The dissociation equation is stated as being:

( 1 PbCl2 (s) <--> 1 Pb^2+ (aq) + 2 Cl- (aq) )

The Khan Academy Ksp appears as follows (8:20):

Ksp = [Pb^2+]^1 * [Cl-]^2

The

*"2"*in 2Cl- is not placed in the brackets, it is only represented as the exponent.

**This is NOT consistent.**

Shouldn't the molar coefficient be placed inside the bracket

*and*in the exponent, also? Please help me to understand.

Sincerely,

-Ariel Morrow