When solid iron(II) hydroxide is added to water, the resulting solution contains

Question

When solid iron(II) hydroxide is added to water, the resulting solution contains 1.4 times 10^-1 g of dissolved iron(ll) hydroxide per liter of solution. What is the hydroxide ion concentration in this solution? 7.8 times 10^-6 M 1.6 times 10^-5 M 2.5 times 10^-10 3.1 times 10^-5 M 4.0 times 10^-3 M Based on the solubility rules, which of the following will occur when solutions of ZnS0_4(aq) and MgCl_2(aq) are mixed? ZnCl_2 will precipitate; Mg^2+ and SO_4^2- will be spectator ions. ZnSO_4 will precipitate; Mg^2+ and Cl^- will be spectator ions.

Explanation / Answer

mass of Fe(OH)2 = 1.4*10^-3 g
Molar mass of Fe(OH)2 = 89.9 g/mol
number of moles of of Fe(OH)2 = mass/molar mass
= (1.4*10^-3)/(89.9)
= 1.56*10^-5 mol

volume = 1 L

[Fe(OH)2] = number of moles/volume
= (1.56*10^-5)/1
= 1.56*10^-5 M

[OH-] = 2*[Fe(OH)2]
= 2*1.56*10^-5 M
= 3.12 *10^-5 M
Answer: D

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