Question

precipitation reactions

1. on the basis of the general solubility rules given in table 4.1,

predict which of the following substances are likely to be sol-
uble in water.
a. aluminum nitrate
b. magnesium chloride
c. rubidium sulfate
d. nickel(ii) hydroxide
e. lead(ii) sulfide
f. magnesium hydroxide
g. iron(iii) phosphate

Explanation:

Step1: Recall solubility rules

• Nitrates (\(NO_3^-\)): All nitrates are soluble.
• Chlorides (\(Cl^-\)): Most chlorides are soluble, exceptions are \(AgCl\), \(PbCl_2\), \(Hg_2Cl_2\).
• Sulfates (\(SO_4^{2 - }\)): Most sulfates are soluble, exceptions are \(BaSO_4\), \(PbSO_4\), \(CaSO_4\) (slightly soluble), \(SrSO_4\).
• Hydroxides (\(OH^-\)): Most hydroxides are insoluble, exceptions are \(NaOH\), \(KOH\), \(Ba(OH)_2\), \(Ca(OH)_2\) (slightly soluble).
• Sulfides (\(S^{2 - }\)): Most sulfides are insoluble (except for group 1 and group 2 sulfides).
• Phosphates (\(PO_4^{3 - }\)): Most phosphates are insoluble (except for group 1 and \(NH_4^+\) phosphates).

Step2: Analyze each compound

• a. Aluminum nitrate (\(Al(NO_3)_3\))

Since it contains the nitrate ion (\(NO_3^-\)), by the nitrate solubility rule, \(Al(NO_3)_3\) is soluble.

• b. Magnesium chloride (\(MgCl_2\))

It contains the chloride ion (\(Cl^-\)). Magnesium is not one of the exceptions (\(Ag^+\), \(Pb^{2+}\), \(Hg_2^{2+}\)) for chloride solubility. So \(MgCl_2\) is soluble.

• c. Rubidium sulfate (\(Rb_2SO_4\))

Rubidium (\(Rb\)) is a group 1 metal. Group 1 sulfates are soluble (since sulfates of group 1 metals do not fall into the sulfate - solubility exceptions). So \(Rb_2SO_4\) is soluble.

• d. Nickel(II) hydroxide (\(Ni(OH)_2\))

It contains the hydroxide ion (\(OH^-\)). Nickel is not one of the exceptions (\(Na^+\), \(K^+\), \(Ba^{2+}\), \(Ca^{2+}\)) for hydroxide solubility. So \(Ni(OH)_2\) is insoluble.

• e. Lead(II) sulfide (\(PbS\))

It contains the sulfide ion (\(S^{2 - }\)). Lead is not a group 1 or group 2 metal. So \(PbS\) is insoluble.

• f. Magnesium hydroxide (\(Mg(OH)_2\))

It contains the hydroxide ion (\(OH^-\)). Magnesium is not one of the exceptions (\(Na^+\), \(K^+\), \(Ba^{2+}\), \(Ca^{2+}\)) for hydroxide solubility. So \(Mg(OH)_2\) is insoluble.

• g. Iron(III) phosphate (\(FePO_4\))

It contains the phosphate ion (\(PO_4^{3 - }\)). Iron is not a group 1 metal or \(NH_4^+\). So \(FePO_4\) is insoluble.

Answer:

a. Soluble; b. Soluble; c. Soluble; d. Insoluble; e. Insoluble; f. Insoluble; g. Insoluble.