1. Introduction to Chemistry
2. The Periodic Table
3. Quantum Numbers
4. Electron Configuration
5. Chemical Families
6. Oxidation Numbers
7. Chemical Formulas
8. Chemical Names
9. Formula Mass
10. Percentage Composition
11. Reaction Types
12. Balancing Equations
13. The Mole Concept
14. Solution Concentration
16. Kinetic Theory
17. The Gas Laws
18. Enthalpy & Heat
19. Reaction Rates
20. Acids & Bases
21. pH Scale
23. Net Ionic Equations
24. Redox Reactions
25. Organic Chemistry
26. Nuclear Chemistry
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.
Naming salts: the name of a salt is related to the name of the acid that forms it.
Examples of Salt Names:
- 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.
- 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
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.
Use these general solublility rules to predict the solubility of salts.
- 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.
Solubility Product Constant, Ksp
If solid silver bromide is placed in water and allowed to stand, it dissolves until an equilibrium exists between the undissolved solid and the ions in solution.
- Given this equilibrium equation:
AgBr(cr) Ag+(aq) + Br−(aq)
- The equilibrium constant expression for the equation is:
- Keq = [products] / [reactants]
- Keq = [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:
Keq[AgBr] = [Ag+] [Br−]
- Keq[AgBr] is the new constant, the solubility product constant, Ksp
Common Ion Effect:
- At room temperature, the Ksp 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.
Titration of Vinegar