Question #7fcb7
1 Answer
Explanation:
The problem wants you to determine the molar solubility of iron(II) hydroxide, which essentially means that you must find the number of moles of iron(II) hydroxide that will dissociate per
Iron(II) hydroxide is considered insoluble in water, which implies that the position of its dissociation equilibrium lies far to the left.
#"Fe"("OH")_ (color(red)(2)(s)) rightleftharpoons "Fe"_ ((aq))^(2+) + color(red)(2)"OH"_ ((aq))^(-)#
In other words, only a very, very small number of moles of iron(II) hydroxide will actually dissociate when dissolved in water.
If you take
#["Fe"^(2+)] = s -># every mole of iron(II) hydroxide that dissociates produces#1# mole of iron(II) cations in solution
#["OH"^(-)] = color(red)(2) * s -># every mole of iron(II) hydroxide that dissociates produces#color(red)(2)# moles of hydroxide anions in solution
Now, the solubility product constant,
#K_(sp) = ["Fe"^(2+)] * ["OH"^(-)]^color(red)(2)#
In your case, this will be equal to
#4.87 * 10^(-17) = s * (color(red)(2)s)^color(red)(2)#
#4.87 * 10^(-17) = 4s^3#
Rearrange to solve for
#s = root(3)( (4.87 * 10^(-17))/4) = 2.30 * 10^(-6)#
This means that a saturated solution of iron(II) hydroxide will contain
In other words, the molar solubility of the salt is equal to
#color(darkgreen)(ul(color(black)("molar solubility" = 2.30 * 10^(-6)color(white)(.)"mol L"^(-1))))#
The answer is rounded to three sig figs.