Chemical and Industrial: July 2012

Chemical classification of detergents

Detergents are classified into three broad groupings, depending on the electrical charge of the surfactants.

Anionic detergents

Typical anionic detergents are alkylbenzenesulfonates. The alkylbenzene portion of these anions is lipophilic and the sulfonate is hydrophilic. Two varieties have been popularized, those with branched alkyl groups and those with linear alkyl groups. The former were largely phased out in economically advanced societies because they are poorly biodegradable An estimated 6 billion kilograms of anionic detergents are produced annually for domestic markets.
Bile acids, such as deoxycholic acid (DOC), are anionic detergents produced by the liver to aid in digestion and absorption of fats and oils.

Three kinds of anionic detergents: a branched sodium dodecylbenzenesulfonate, linear sodium dodecylbenzenesulfonate, and a soap.

Cationic detergents

Cationic detergents are similar to the anionic ones, with a hydrophobic component, but, instead of the anionic sulfonate group, the cationic surfactants have quaternary ammonium as the polar end. The ammonium center is positively charged.

Non-ionic and zwitterionic detergents

Non-ionic detergents are characterized by their uncharged, hydrophilic headgroups. Typical non-ionic detergents are based on polyoxyethylene or a glycoside. Common examples of the former include Tween, Triton, and the Brij series. These materials are also known as ethoxylates or PEGylates). Glycosides have a sugar as their uncharged hydrophilic headgroup. Examples include octyl-thioglucoside and maltosides. HEGA and MEGA series detergents are similar, possessing a sugar alcohol as headgroup.
Zwitterionic detergents possess a net zero charge arising from the presence of equal numbers of +1 and -1 charged chemical groups. Examples include CHAPS.

Detergent

A detergent is a surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." These substances are
usually alkylbenzenesulfonates, a family of compounds that are similar to soap but are more soluble in hard water, because the polar sulfonate (of detergents) is less likely than the polar carboxyl (of soap) to bind to calcium and other ions found in hard water. In most household contexts, the term detergent by itself refers specifically to laundry detergent or dish detergent, as opposed to hand soap or other types of cleaning agents. Detergents are commonly available as powders or concentrated solutions. Detergents--like soaps-- work because they are amphiphilic - partly hydrophilic (polar) and partly hydrophobic (non-polar). Their dual nature facilitates the mixture of hydrophobic compounds (like oil and grease) with water. Because air is not hydrophilic, detergents are also foaming agents to varying degrees.

Quantitative notation

There are four quantities that describe concentration:

Mass concentration

Main article: Mass concentration (chemistry)

The mass concentration $\rho_i$ is defined as the mass of a constituent $m_i$ divided by the volume of the mixture $V$ :

$\rho_i = \frac {m_i}{V}$

The SI-unit is kg/m³.

Molar concentration

Main article: Molar concentration

The molar concentration $c_i$ is defined as the amount of a constituent $n_i$ divided by the volume of the mixture $V$ :

$c_i = \frac {n_i}{V}$

The SI-unit is mol/m³. However, more commonly the unit mol/L (= mol/dm³) is used.

Number concentration

Main article: Number concentration

The number concentration $C_i$ is defined as the number of entities of a constituent $N_i$ in a mixture divided by the volume of the mixture $V$ :

$C_i = \frac{N_i}{V}$

The SI-unit is 1/m³.

Volume concentration

Main article: Volume concentration

The volume concentration $\phi_i$ (also called volume fraction) is defined as the volume of a constituent $V_i$ divided by the volume of all constituents of the mixture $V$ prior to mixing:

$\phi_i = \frac {V_i}{V}$

The SI-unit is m³/m³.

Qualitative description

Often in informal, non-technical language, concentration is
described in a qualitative way, through the use of adjectives such as "dilute" for solutions of relatively low concentration and "concentrated" for solutions of relatively high concentration. To concentrate a solution, one must add more solute (for example, alcohol), or reduce the amount of solvent (for example, water). By contrast, to dilute a solution, one must add more solvent, or reduce the amount of solute. Unless two substances are fully miscible there exists a concentration at which no further solute will dissolve in a solution. At this point, the solution is said to be saturated. If additional solute is added to a saturated solution, it will not dissolve, except in certain circumstances, when supersaturation may occur. Instead, phase separation will occur, leading to coexisting phases, either completely separated or mixed as a suspension. The point of saturation depends on many variables such as ambient temperature and the precise chemical nature of the solvent and solute.

Normal Solution

In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Furthermore, in chemistry, four types of mathematical description can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration. The term concentration can be applied to any kind of chemical mixture, but most frequently it refers to solutes in solutions.

Normality

Normality is defined as the molar concentration $c_i$ divided by an equivalence factor $f_\mathrm{eq}$ . Since the definition of the equivalence factor may not be unequivocal, IUPAC and NIST discourage the use of normality.

Sunday, July 22, 2012