LEARNING OBJECTIVES
By the end of this topic, you are expected to;
In chemistry, salt refers to a solid chemical compound that is made up of an ionic assembly of anions and cations. Salts are made up of related numbers of cations (positively charged ions) and anions (negatively charged ions) so that the product is electrically neutral. This means that it does not have a net charge. These component ions may be inorganic, like chloride, or organic, like acetate (CH3CO2)-; and can be monatomic, like fluoride (F-) or polyatomic, like sulfate (SO42-).
TYPES OF SALTS
Salts can be classified in different ways. Salts that produce hydroxide ions when dissolved in water are known as alkali salts. Salts that produce acidic solutions are known as acid salts. Neutral salts are those that are neither basic nor acidic. Zwitterions contain a cationic and an anionic center in the same molecule, but they are not considered to be salts. Many proteins, peptides, metabolites, and amino acids are examples of zwitterions.
PROPERTIES
COLOR. Solid salts are mainly transparent as illustrated by sodium chloride. In most cases, the apparent transparency or opacity is only related to the difference in the size of the individual monocrystals. Since light reflects from the grain boundaries, larger crystals tend to be transparent, while the polycrystalline aggregates look like white powders.
Salts exist in different colors. These colors may arise from the cations or anions. For example:
TASTE. Different salts can show all five basic tastes. For example, sodium chloride is sweet, lead diacetate is sour and potassium bitartrate is bitter.
ODOR. Salts of strong acids and strong bases (which are known as strong salts) are non-volatile and often odorless, whereas salts of either weak acids or weak bases may smell like the conjugate acid.
SOLUBILITY. Many ionic compounds show significant solubility in water or other polar solvents. Unlike molecular compounds, salts dissociate in solution into cationic and anionic components. The lattice energy, the cohesive forces between these ions within a solid, determines the solubility.
CONDUCTIVITY. Salts are characteristically insulators. Molten salts or solutions conduct electricity. For this reason, molten salts and solutions containing dissolved salts (like sodium chloride in water) are called electrolytes.
MELTING POINT. Salts characteristically have high melting points. For example, sodium chloride melts at 801⁰ C. Some salts with low lattice energies are liquid at or near room temperature. These include molten salts, which are usually mixtures of ionic liquids and salts, which usually contain organic cations. These liquids show unusual properties as solvents.
NOMENCLATURE
The name of salt begins with the name of the cation such as ammonium or sodium followed by the name of the anion such as acetate or chloride. Salts are mainly referred to only by the name of the anion such as acetate salt or chloride salt.
Common salt-forming cations include:
Common salt-forming anions include (parent acids in parentheses where available):
FORMATION
Salts can be formed through a chemical reaction between:
