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: $C<em>2H</em>3O_2^-$ (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 ($PbSO<em>4$), Mercury(I) chloride ($Hg</em>2Cl_2$), 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 ($CaSO<em>4$), Strontium sulfate ($SrSO</em>4$), 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.