Practice MCQ Questions and answers on Chemistry-GK

Milk is emulsion.

An emulsion is a mixture of two or more liquids that are normally immiscible (nonmixable or unblendable). Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion should be used when both the dispersed and the continuous phase are liquids. In an emulsion, one liquid (the dispersed phase) is dispersed in the other (the continuous phase). Examples of emulsions include vinaigrettes, milk, mayonnaise, and some cutting fluids for metal working. The photo-sensitive side of photographic film is also an example of a colloid. The word “emulsion” comes from the Latin word for “to milk”, as milk is (among other things) an emulsion of milk fat and water.

An emulsifier is a substance that stabilizes an emulsion by increasing its kinetic stability. One class of emulsifiers is known as “surface active substances”, or surfactants. Many different emulsifiers are used in pharmacy to prepare emulsions such as creams and lotions. Common examples include emulsifying wax, cetearyl alcohol, polysorbate 20, and ceteareth 20. Sometimes the inner phase itself can act as an emulsifier, and the result is a nanoemulsion, where the inner state disperses into “nano-size” droplets within the outer phase. A well-known example of this phenomenon, the “Ouzo effect”, happens when water is poured into a strong alcoholic anise-based beverage, such as ouzo, pastis, arak, or raki. The anisolic compounds, which are soluble in ethanol, then form nano-size droplets and emulsify within the water. The resulting colour of the drink is opaque and milky white.

Natural and wastewater contain small particulates that are suspended in water forming a colloid. These particles carry the same charges, and repulsion prevents them from combining into larger particulates to settle. Historically, dirty water is cleaned by treating with alum, Al₂(SO₄)₃.12 H₂O, and lime, Ca(OH)₂. The phenomenon is known as coagulation.

A gel is a solid, jelly-like material that can have properties ranging from soft and weak to hard and tough. Gels consist of a solid three-dimensional network that spans the volume of a liquid medium and ensnares it through surface tension effects. Shaving creams in a can are commonly dispensed as a foam or a gel.

A colloidal dispersion in which the dispersed particles are more or less liquid and exert a certain attraction on and absorb a certain quantity of the fluid in which they are suspended is called as hydrophilic colloid. Molecules of a hydrophilic colloid have an affinity for water molecules and when dispersed in water become hydrated. Hydrated colloids swell and increase the viscosity of the system, thereby improving stability by reducing the interaction between particles and their tendency to settle. They may also possess a net surface electrical charge. The charge sign depends on the chemical properties of the colloid and the pH of the system. The presence of a surface charge produces repulsion of the charged particles and thus reduces the likelihood that the particles will adhere to one another and settle. Some examples of hydrophilic colloids used in pharmacy are acacia, methylcellulose, and proteins, such as gelatin and albumin.

Peptization or Deflocculation is the process responsible for the formation of converting precipitate into colloid by shaking with it an electrolyte. This is particularly important in colloid chemistry or for precipitation reactions in an aqueous solution.

Espuma is a Spanish term for froth or foam, and one that is created specifically with the use of a siphon bottle. Espuma is created mainly with liquid that has air incorporated in it to create froth. This is a specific term, since culinary foams may be attained through other means.

Cloud is a colloidal dispersion of water drops in a dispersion medium of water.