For the first part, we’re being asked to calculate the solubility of Mg(OH)2 in 0.160 M NaOH. Since the compounds are ionic compounds, they form ions when dissociating in water. The dissociation of CaF2 and NaF in water are as follows:
Magnesium is in Group 2A so its charge is +2. Hydroxide is a polyatomic ion (OH–) so its charge is –1:
Mg(OH)2(s) ⇌ Mg2+(aq) + 2 OH–(aq)
Sodium is in Group 1A so its charge is +1. Hydroxide is a polyatomic ion (OH–) so its charge is –1:
NaOH(s) → Na+(aq) + OH–(aq)
Notice that there is a common ion present, OH–. The common ion effect states that the solubility of a salt is lower in the presence of a common ion.
We can construct an ICE table for the dissociation of Mg(OH)2. Remember that solids are ignored in the ICE table.
Based on the given value of the Ksp, what is the molar solubility of Mg(OH)2 in 0.160 M NaOH? Express your answer with the appropriate units.
Calculate how many times more soluble Mg(OH)2 is in pure water.
Based on the given value of the Ksp, calculate the ratio of solubility of Mg(OH)2 dissolved in pure H2O to Mg(OH)2 dissolved in a 0.160 M NaOH solution. Express your answer numerically to three significant figures.
Ksp = 5.61×10−11.
Frequently Asked Questions