Chemistry Aqueous Solutions: Electrolytes, Solubility Rules & Net Ionic Equations

Aqueous solution, and what (aq) means

A solution with water as the solvent. (aq) after a formula means the compound is dissolved in water; (s) means it stays solid

Dissociation of an ionic compound in water

The compound separates into individual ions that spread out among the water molecules

Hydrated ions

Ions surrounded by water molecules after an ionic compound dissolves

Electrolyte

A substance that conducts electricity when dissolved in water, because of mobile ions

Strong electrolyte

Dissociates or ionizes 100% in water and conducts electricity well. Includes ionic compounds (salts), strong bases, and strong acids

Weak electrolyte

Only partly ionizes in water, so it conducts electricity only slightly. Includes weak acids and weak bases

Nonelectrolyte

Dissolves as molecules and does not conduct electricity. Most molecular compounds that are not acids or bases (e.g. sugars like C6H12O6)

The 7 strong acids

HCl, HBr, HI, HNO3, HClO4, HClO3, H2SO4

Weak acid

Any acid that is not one of the 7 strong acids. Ionizes only partially, so it mostly stays as molecules (e.g. HNO2, H3PO4). A weak electrolyte

Strong base

An ionic compound containing the hydroxide ion (e.g. NaOH, KOH). Dissociates 100% in water. A strong electrolyte

Weak base

A molecular compound (e.g. NH3, CH3NH2) that reacts with water only slightly to make hydroxide ions. A weak electrolyte

Solubility rule 1

Compounds of group 1 cations (Li+, Na+, K+, Rb+, Cs+, Fr+) and NH4+ are soluble

Solubility rule 2

Nitrates (NO3-), chlorates (ClO3-), perchlorates (ClO4-), and acetates (C2H3O2-) are soluble

Solubility rule 3

Chlorides (Cl-), bromides (Br-), and iodides (I-) are soluble, except those of Ag+, Pb2+, and Hg2 2+

Solubility rule 4

Carbonates (CO3 2-), sulfites (SO3 2-), phosphates (PO4 3-), and chromates (CrO4 2-) are insoluble, except with group 1 cations (and NH4+)

Solubility rule 5

Hydroxides (OH-) and sulfides (S2-) are insoluble, except with group 1 cations (and NH4+) and Ba2+

Solubility rule 6

Ag+, Hg2 2+, and Pb2+ salts are insoluble, except those covered by rule 2 (nitrates, chlorates, perchlorates, acetates)

Solubility rule 7

Sulfates (SO4 2-) are soluble, except those of Ca2+, Sr2+, Ba2+, Ag+, Hg2 2+, and Pb2+

Solubility amounts in Table 8.5

s = soluble (more than about 1 g per 100 g water); ss = slightly soluble (about 0.1 to 1 g); i = insoluble (less than about 0.1 g); d = decomposes in water

Soluble vs. insoluble ionic compounds

Soluble ones readily dissolve in water; insoluble ones do not (though even insoluble ones dissolve to a very small degree)

Precipitation reaction

A double-replacement reaction in which two ionic solutions are mixed and form an insoluble ionic compound

Precipitate

The insoluble solid that forms in a precipitation reaction (it makes the mixture look cloudy)

Total (molecular) equation

Shows the complete formula of every reactant and product

Ionic equation

Shows all aqueous strong electrolytes as separate ions

Net ionic equation

The ionic equation with the spectator ions removed, showing only the species that changed

Spectator ion

An ion that appears unchanged on both sides of the ionic equation and does not take part in the reaction

What stays as a whole formula in an ionic equation?

Solids (s), liquids (l), gases (g), and weak electrolytes or molecular compounds. Only aqueous strong electrolytes are split into ions