Liquids are the material substances which have a tendency to flow.
They occupy the shape of the vessel they are poured into.
They can flow on surface due to loose arrangement of molecules within the matter.
They have less inter-molecular forces of attraction than solids.
Hence unlike solids, they cannot retain a shape.
They just tend to spread on the surface without any shape.
On the other hand, gases have further weaker forces of attraction in between molecules.
Hence they vaporize on exposure to air.
Types of liquids:
In nature liquids are available as different types as below.
5. Aerated liquids.
Solvents: These are the true liquids among the list. These are liquids which have only one set of molecules. They are present in large quantities in nature. In-fact they are most common liquids we encounter in every day life.
Ex: Water, plant oils, mineral oils, organic solvents like benzene, carbon tetra-chloride, acetone etc.
These solvents form all the other type of liquids mentioned above. Without these solvents, other liquids are impossible to make or form.
These solvents are again of many types and differentiated based on their chemistry, nature, polarity, pH etc. Also see types of solvents.
Solutions: These are liquids which have other substances within the inter molecular spaces. When you mix sugar or salt into water, you make a solution. Sea water is an example of natural solution.
When the substance is mixed into water (solvent), the molecules of the substances get separated from each other. Then these separated molecules of solid substance, arrange themselves within the spaces of solvent molecules.
Thus you can notice that when you add table salt to a glass full of water, it does not immediately overflow. It overflows only after certain amount of salt is already added. That is, it is the amount of salt which can occupy the space in between water molecules. Then the when remaining salt is added, it overflows the water for extra space in the glass.
Emulsions: These are special types of liquids where in two immiscible liquids are mixed up. One liquid is evenly distributed as globules into another.
In nature we can see it in the form of butter. Even when we wash our hands with soap, it removes the oil due to formation of emulsion.
These emulsions are of two types as Water in Oil (W/O) type or Oil in Water (O/W) type. In water in Oil type, the water is distributed as fine globules into Oil. While in the other, it is vice-verse.
These are further made into w/o/w (water in oil in water) type or o/w/w (oil in water in oil type). These are called as complex emulsions and have less stability.
Many drugs are formulated in emulsion type as they are insoluble. Hence emulsions serve as drug delivery systems.
Suspensions: As the name indicates, these are liquids where in solid particles are suspended in solvent.
These suspensions have fine particle matter dispersed evenly within a solvent. These are less common in nature. But they are widely used by humans in medicine forms. We can see many drug
preparations like ant-acids in the suspension form. These suspensions have a character of particle settlement. The suspended particles settle down at the bottom if kept still for a long time. Hence the label carry instructions to “Shake well before Use”.
Also muddy water, water mixed with fine sand (silt) are also naturally available suspensions. But on standing the particles may settle. Now a days, nano-particle based suspensions are also made. These do not settle as much as those suspensions with bigger particle size.
Aerated solutions: These are also less common in nature but are readily available as beverages to humans. The Coke and soda which see in daily life are examples. Here gas is entrapped within the liquid spaces. This gas gets expelled at warm temperature.
They are similar to solutions with the only difference that instead of solid being mixed, gas is mixed with liquid. But unlike solutions, they have few differences in behavior. When shaken, the gas molecules get together to form bubbles. These bubbles put pressure on the solvent to expel it forcefully from the container. Hence we can notice foam when shaken.