What concentration of #"SO"_3^(2–)# is in equilibrium with #"Ag"_2"SO"_3(s)# and #1.80 * 10^-3# #"M"# #"Ag"^(+)# ? The #K_(sp)# of #"Ag"_2"SO"_3# is #1.50 * 10^–14#
One last question from me. I thought it would be Ksp=[2Ag^+]^2[SO3^2-], but plugging in 1.80×10^-3 for Ag and doing algebra doesn't seem to get me the correct answer when I put it on the online homework tool we use. Thanks for your help! I still can't seem to understand concentrations.
One last question from me. I thought it would be Ksp=[2Ag^+]^2[SO3^2-], but plugging in 1.80×10^-3 for Ag and doing algebra doesn't seem to get me the correct answer when I put it on the online homework tool we use. Thanks for your help! I still can't seem to understand concentrations.
1 Answer
Explanation:
The expression of the solubility product constant for silver sulfite looks like this
#K_(sp) = ["Ag"^(+)]^color(red)(2) * ["SO"_3^(2-)]#
This is the case because silver sulfite will partially ionize to produce silver(I) cations and sulfite anions in aqueous solution.
#"Ag"_ 2"SO"_ (3(s)) rightleftharpoons color(red)(2)"Ag"_ ((aq))^(+) + "SO"_ (3(aq))^(2-)#
Notice that the fact that every mole of silver sulfite that dissociates in aqueous solution produce
Mind you, the coefficients of the ions are used as expoents in the expression of the solubility product constant, not as coefficients.
So something like
#K_(sp) = [color(red)(2)"Ag"^(+)]^color(red)(2) * ["SO"_3^(2-)]#
is not correct because the coefficient must only be used as an exponent in the expression of the solubility proeduct constant.
In your case, you have--I'll do the calculations with the added units for the solubility product constant!
#1.50 * 10^(-14) quad "M"^3 = (1.80 * 10^(-3))^color(red)(2) quad "M"^color(red)(2) * ["SO"_3^(2-)]#
So you can say that the equilibrium concentration of the sulfite anions will be equal to
#[S"O"_3^(2-)] = (1.50 * 10^(-14) quad "M"^color(red)(cancel(color(black)(3))))/((1.80 * 10^(-3))^color(red)(2) quad color(red)(cancel(color(black)("M"^2)))) = color(darkgreen)(ul(color(black)(4.63 * 10^(-9) quad "M")))#
The answer is rounded to three sig figs.
So, a quick recap
#"Ag"_ 2"SO"_ (3(s)) rightleftharpoons color(red)(2)"Ag"_ ((aq))^(+) + "SO"_ (3(aq))^(2-)# Here
#color(red)(2)# is a coefficient!
#K_(sp) = ["Ag"^(+)]^color(red)(2) * ["SO"_3^(2-)]# Here
#color(red)(2)# must be an exponent, so don't use it as a coefficient!