Salts are crystalline compounds composed of the negative ion of an acid and the positive ion of a base.

The reaction of a base and an acid to produce a salt and water is neutralization.

While the reaction above usually comes to mind when salt production is mentioned, there are many reactions that produce salts. It is even possible to have salts that do not produce neutral solutions.

Salts can also be formed by the reaction of an acidic or basic anhydride with a corresponding base, acid, or anhydride.

• acidic anhydride + base → salt
  SO₃ + 2NaOH → Na₂SO₄ + H₂O

• basic anhydride + acid → salt
  Na₂O + H₂SO₄ → Na₂SO₄ + H₂O

• basic anhydride + acidic anhydride → salt
  Na₂O + SO₃ → Na₂SO₄

Certain acids and bases react to produce only a partial neutralization. These reactions produce either acidic salts or basic salts.

• This reaction produces an acidic salt:
  H₂SO_{4 (aq)} + NaOH _(aq) → NaHSO_{4 (aq)} + H₂O _(l)

  Sodium hydrogen sulfate is an acidic salt because it still contains an ionizable hydrogen atom.

Naming salts: the name of a salt is related to the name of the acid that forms it.

• Binary acids produce salts ending with -ide.
   
• Ternary acids ending in -ic produce salts ending with -ate.
   
• Ternary acids ending in -ous produce salts ending with -ite.
   
• Any prefixes in the ternary acid remain in the salt name.
   
• In naming acidic and basic salts, each ion in the salt is named separately.
   
  • Hydrogen is named immediately before the names of any negative ions.

    A prefix is used to indicate more than one hydrogen.
     

  • Hydroxide is named immediately after the names of any positive ions.

    The hydroxide is commonly placed in parenthesis.

• CaCl₂ - calcium chloride
• K₂SO₄ - potassium sulfate
• NaHC₂O₄ - sodium hydrogen oxalate
• NaHS - sodium hydrogen sulfide
• NaH₂PO₄ - sodium dihydrogen phosphate
• Sn(OH)NO₃ - tin (II) hydroxide nitrate

Naming Salts

 
For about 95% of all compounds, solubility in water increases with increasing temperature. Many compounds can have their solubility in water increased or decreased by the presence of another solute.

Solubilities can be broken into four general classes:

• soluble - all of the material dissolves and does so fairly quickly.
   
• slightly soluble - some of the material visibly dissolves over a period of time.
   
• sparingly soluble - the materials has a very low solubility, such as 0.5 g per liter.
   
• insoluble - none of the material dissolves.

• Salts of group 1 and ammonia are soluble.
   
• Acetates and nitrates are soluble.
   
• Binary compounds of group 17, except F, are soluble with metals, except Ag, Hg⁺, and Pb.
   
• All sulfates are soluble, except those of Ba, Sr, Pb, Ca, Ag, and Hg⁺.
   
• Except for those in rule 1, carbonates, hydroxides, oxides, sulfides, and phosphates are insoluble.

Salt Solubility

 
Solubility Product Constant, K_sp

• Given this equilibrium equation:
  AgBr_(cr) Ag⁺_(aq) + Br⁻_(aq)  
• The equilibrium constant expression for the equation is:
   
  • K_eq = [products] / [reactants]
     
  • K_eq = [Ag⁺] [Br⁻] / [AgBr]
     
  • Remember that the brackets, [ ], indicate "concentration".
   
• Since AgBr is a solid substance, its concentration is constant. The equilibrium constant expression can therefore be manipulated to read:
  K_eq[AgBr] = [Ag⁺] [Br⁻]  
• K_eq[AgBr] is the new constant, the solubility product constant, K_sp

• At room temperature, the K_sp of silver bromide is 5.01 X 10⁻¹³
• Using the equilibrium constant expression, [Ag⁺] [Br⁻] = 5.01 X 10⁻¹³
• The concentration of both ions are the same, [Ag⁺]² = 5.01 X 10⁻¹³
• The square root of 5.01X10⁻¹³ gives:
  [Ag⁺] = 7.08 X 10⁻⁷M, which is also the [Br⁻]  

The addition of a substance containing an ion already at equilibrium in a saturated solution will shift the equilibrium toward the undissolved substance. Another way to say this is that the addition of a common ion decreases the solubility of a substance in solution.

 
K_sp Problems

 
Titration of Vinegar