how do you do ksp problems?

[mrh125]

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like if you had 4Pb^(2+) + 2S^(2-)

how would you figure out how to write the concentrations to solve for the ksp? it always threw me off how to determine the coefficients and the exponents when writing these.

would it be [4s]^2*[2s]^2=ksp? this seriously confuses me

 

[Teleologist]

Concentrations for aqueous substances are generally expressed as molarities, or in terms of moles of solute per volume (liter) of solvent.

 

[mrh125]

Concentrations for aqueous substances are generally expressed as molarities, or in terms of moles of solute per volume (liter) of solvent.

ok but how do you determine the numbers of the coefficient and in the exponent?

 

[jayoh]

the expression would be

Ksp = [Pb]^4 * [.S]^2

Plug in the concentrations to solve for the Ksp. If you're trying to solve for the molar solubility of just one of the components, you have to introduce the 2s^2 stuff. Hope that helps

 

[mrh125]

the expression would be

Ksp = [Pb]^4 * [.S]^2

Plug in the concentrations to solve for the Ksp. If you're trying to solve for the molar solubility of just one of the components, you have to introduce the 2s^2 stuff. Hope that helps

so we just use the coefficients and ignore the exponents unless we are calculating molar solubility?

 

[getsome111]

im not sure how you are going about learning this, but in my mind is so infinitely better to sit around for awhile and learn why an equation is written a specific way rather than just attempting to match a pattern. solving the problems isn't going to help you too much unless you can understand whats going on, that said, the solubility product Ksp is basically a number which represents the molar concentrations of the precipitate forming reactants(at their threshold concentrations of forming a precipitate) multiplied together, a "product" of them, this is why you will take your coefficients from the balanced reaction and move them to the exponent position. precipitate product A2C3 results is described by the Ksp equation(assuming A and C are both in aqueous solution)

Ksp = [A][A][C][C][C]

because it takes 2As and 3Cs to form one molecule of product the ksp value was created as a multiple of every concentration species involved, thus you get what you were asking about earlier

Ksp = [A]^2[C]^3

edit: example was As and Bs but I guess that causes my text to be bolded

 

[Blueprint MCAT Tutor]

Your question looks kind of odd to me, but here's my take on it:

http://i.imgur.com/j88MJZC.png

More important that the specific example of tetra lead disulfide is the basic four steps I listed in the picture.

Hope this helps!

 

[mrh125]

Your question looks kind of odd to me, but here's my take on it:

http://i.imgur.com/j88MJZC.png

More important that the specific example of tetra lead disulfide is the basic four steps I listed in the picture.

Hope this helps!

wow that's so weird. thanks. does the charge mean anything at all in the solving process? o.0

 

[Blueprint MCAT Tutor]

does the charge mean anything at all

Nope. Well, at least not for this kind of problem. It can matter but it doesn't here.