Solubility Rules Lecture Notes

Solubility Rules: Nag Sag Mnemonic

Introduction

The mnemonic "Nag Sag" is used to easily remember solubility rules in chemistry. This helps in recalling which molecules or substances are generally soluble.

Nag Sag - Always Soluble

Nag Sag represents the molecules that are generally soluble. This means that compounds containing these ions are likely to dissolve in water.

• N - Nitrates: NO_3^- (nitrate ion)

• A - Acetates: C2H3O_2^- (acetate ion)

• G - Group 1 Metals: such as Lithium (Li), Sodium (Na), Potassium (K), etc.

• S - Sulfates: SO_4^{-2} (sulfate ion)

• A - Ammonium: NH_4^+ (ammonium ion)

• G - Group 17 Nonmetals (Halides): such as Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), etc.

Exceptions to Solubility - PMS

While Nag Sag molecules are generally soluble, there are exceptions, primarily related to Sulfates and Group 17 nonmetals. The first group of exceptions is referred to as PMS:

• P - Lead: Pb^{+2} (lead(II) ion)

• M - Mercury: Hg_2^{+2} (mercury(I) ion)

• S - Silver: Ag^{+} (silver ion)

Incompatibility with Sulfates and Group 17 Nonmetals

• PMS compounds are not soluble when combined with Sulfates (SO_4^{-2}) or Group 17 nonmetals (Halides).

• For instance, Lead(II) sulfate (PbSO4), Mercury(I) chloride (Hg2Cl_2), and Silver iodide (AgI) are insoluble compounds.

Exceptions to Solubility - Castorware

The second group of exceptions is called Castorware, referring to certain alkaline earth metals:

• Castorware: Calcium, Strontium, and Barium

  • Calcium (Ca^{+2})

  • Strontium (Sr^{+2})

  • Barium (Ba^{+2})

Incompatibility with Sulfates

• Castorware elements/ions are not soluble when combined with sulfates (SO_4^{-2}).

• For instance, Calcium sulfate (CaSO4), Strontium sulfate (SrSO4), and Barium sulfate (BaSO_4) are insoluble compounds.

Summary

Nag Sag is a helpful mnemonic, but it's essential to remember the exceptions (PMS and Castorware) to accurately predict solubility. Solubility rules are crucial in predicting whether a precipitate will form when aqueous solutions are mixed.