Solubility Rules and Common Polyatomic Ions

Vocabulary flashcards covering general solubility rules and common polyatomic ion names and formulas.

Table 2.5 Common Polyatomic Ions

A reference chart listing common polyatomic ions, their chemical formulas, and their corresponding names.

Solubility Rule 1 (Nitrates)

Most nitrate ($\text{NO}_3^-$) salts are soluble.

Solubility Rule 2 (Alkali Metals and Ammonium)

Most alkali metal (group 1A) salts and $\text{NH}_4^+$ are soluble.

Solubility Rule 3 (Halides)

Most $\text{Cl}^-$, $\text{Br}^-$, and $\text{I}^-$ salts are soluble (except $\text{Ag}^+$, $\text{Pb}^{2+}$, $\text{Hg}_2^{2+}$).

Solubility Rule 4 (Sulfates)

Most sulfate salts are soluble (except $\text{BaSO}_4$, $\text{PbSO}_4$, $\text{Hg}_2\text{SO}_4$, $\text{CaSO}_4$).

Solubility Rule 5 (Hydroxides)

Most $\text{OH}^-$ are only slightly soluble ($\text{NaOH}$, $\text{KOH}$ are soluble, $\text{Ba(OH)}_2$, $\text{Ca(OH)}_2$ are (marginally) soluble). For CHEM 111/105/106, treat slightly as insoluble and marginally as soluble.

Solubility Rule 6 (Sulfides, Carbonates, Chromates, Phosphates)

Most $\text{S}^{2-}$, $\text{CO}_3^{2-}$, $\text{CrO}_4^{2-}$, $\text{PO}_4^{3-}$ salts are only slightly soluble, except for those containing the cations in Rule 2.

Mercury(I)

$$\text{Hg}_2^{2+}$$

Ammonium

$$\text{NH}_4^+$$

Nitrite

$$\text{NO}_2^-$$

Nitrate

$$\text{NO}_3^-$$

Sulfite

$$\text{SO}_3^{2-}$$

Sulfate

$$\text{SO}_4^{2-}$$

Hydrogen sulfate

$\text{HSO}_4^-$ (bisulfate is a widely used common name)

Hydroxide

$$\text{OH}^-$$

Cyanide

$$\text{CN}^-$$

Phosphate

$$\text{PO}_4^{3-}$$

Hydrogen phosphate

$$\text{HPO}_4^{2-}$$

Dihydrogen phosphate

$$\text{H}_2\text{PO}_4^-$$

Thiocyanate

$\text{NCS}^-$ or $\text{SCN}^-$

Carbonate

$$\text{CO}_3^{2-}$$

Hydrogen carbonate

$\text{HCO}_3^-$ (bicarbonate is a widely used common name)

Hypochlorite

$\text{ClO}^-$ or $\text{OCl}^-$

Chlorite

$$\text{ClO}_2^-$$

Chlorate

$$\text{ClO}_3^-$$

Perchlorate

$$\text{ClO}_4^-$$

Acetate

$$\text{C}_2\text{H}_3\text{O}_2^-$$

Permanganate

$$\text{MnO}_4^-$$

Dichromate

$$\text{Cr}_2\text{O}_7^{2-}$$

Chromate

$$\text{CrO}_4^{2-}$$

Peroxide

$$\text{O}_2^{2-}$$

Oxalate

$$\text{C}_2\text{O}_4^{2-}$$

Thiosulfate

$$\text{S}_2\text{O}_3^{2-}$$