Chemistry > Surface Chemistry > 9.0 Emulsions
Surface Chemistry
1.0 Introduction
2.0 Adsorption
3.0 Factors affecting adsorption of gases by solids
4.0 Adsorption Isotherms
5.0 Applications of Adsorption
6.0 Types of Solutions
7.0 Colloidal System
7.1 Different Colloidal Systems
7.2 Classification of Colloidal System
7.3 Preparation of Colloidal System
7.4 Purification of Colloidal System
7.5 Properties of colloidal system
8.0 Coagulation of colloidal solutions
9.0 Emulsions
10.0 Catalysis
11.0 Zeolites as shape-selective catalysts
12.0 Enzyme as catalysts
12.1 Characteristics of Enzymes
12.2 Mechanism of enzyme catalysis
12.3 Autocatalysis
12.4 Induced catalysis
9.2 Applications of colloids and emulsions
7.2 Classification of Colloidal System
7.3 Preparation of Colloidal System
7.4 Purification of Colloidal System
7.5 Properties of colloidal system
12.2 Mechanism of enzyme catalysis
12.3 Autocatalysis
12.4 Induced catalysis
1. Colloids in nature
- Foodstuffs
Many of our foodstuffs are colloidal in nature. For example, milk is an emulsion of fat dispersed in water and stabilised by casein which itself is a lyophilic colloids. Other foodstuffs, colloidal in nature are eggs, fruit jellies, whipped cream etc.
- Medicines
A great number of medicinal and pharmaceutical preparations are emulsions such as the cod liver oil and halibut liver oil. It is believed that the emulsified oils are easily acted upon by the digestive juices in the stomach and hence are readily digested.
- Soils
Good soils are colloidal in nature in which humus acts as a protective colloid. On account of their colloidal nature, they can retain more moisture for emergency and moreover the nourishing materials are supplied to the plant by the process of adsorption.
- Industrial goods
Soaps, detergents and wetting agents are colloidal electrolytes. Paints, varnishes, enamels, cellulose, resins, gums, glues and other adhesives, rayon, nylon, terylene, textiles, leather, etc. are all colloidal in nature.
2. Purification of water
The impure water contains clay particles and bacteria. The presence of clay particles is responsible for the turbidity in water. The addition of potash alum or aluminium sulphate furnishes the trivalent aluminium ions which cause the coagulation of the clay particles.
3. Sewage disposal
Sewage water contains dirt, rubbish, mud etc. which are of colloidal size and carry electric charge and, therefore, do not settle down easily. These particles can be removed by the process of cataphoresis in which sewage water is passed through a tunnel fitted with metallic electrodes, maintained at high potential difference. The particles migrate to the oppositely charged electrodes, get neutralised and settle down. The deposited matter is used as a manure and the clear water is used for irrigation purposes.
4. Smoke precipitation
Smoke particles are actually electrically charged colloidal particles of carbon in the air. Precipitation of smoke is carried out by Cottrell precipitator which is based on the principle of electrophoresis.
Smoke is allowed to pass through a chamber having a number of metal plates attached to a metal wire connected to a source of high potential. Charged particles of smoke get attached by oppositely charged electrode, get precipitated after losing their charge and the hot air passes out through the chimney. The dust particles are also removed in this process. Thus, the nuisance of smoke in big industrial cities can be avoided.
5. Cleansing action of soap
Soap solution is colloidal in nature. It removes the dirt particles either by adsorption or by emulsifying the greasy matter sticking to the cloth.
6. Rubber plating and chrome tanning
In rubber plating, the negatively charged particles of rubber (latex), are made to deposit on the wires or handle of various tools by means of electrophoresis. The article on which rubber is to be deposited is made anode.
In tanning, the positively charged colloidal particles of hides and leather are coagulated by impregnating them in negatively charged tanning materials. Among the tanning agents, chromium salts are most commonly used for the coagulation of the hide material and the process is called chrome tanning. The rate of chrome tanning can be increased by electrophoresis.
7. Delta formation
River water contains charged colloidal particles of clay, sand and many other materials. Sea water is a very big store-house of a variety of electrolytes dissolved in it. As soon as river water comes in contact with sea water, the electrolytes present in sea water coagulate the suspended colloidal particles which ultimately settle down at the point of contact. Thus, the level of the river bed rises. As a result, water adopts a different course and delta is formed in due course of time. It is so called because the heap formed has a shape similar to the Greek letter $\delta$. In other words, delta is formed due to silting of the estuary (i.e. deposit of sediment at the mouth of the river).
8. Smoke screens
Smoke screens are used in warfare for the purpose of concealment. These screens consist of very fine particles of titanium oxide dispersed in air. These are dropped from aeroplanes and since titanium oxide is very heavy, the smoke screen drops rapidly as a curtain of dazzling whiteness.
