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 a surface due to the loose arrangement of molecules within the matter.
They have fewer inter-molecular forces of attraction than solids.
Hence unlike solids, they cannot retain a shape on their own.
They 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 in 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 everyday life.
Ex: Water, plant oils, mineral oils, organic solvents like benzene, carbon tetrachloride, acetone, etc.
These solvents form all the other type of liquids mentioned above. Without these solvents, other liquids are impossible to be made.
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 intermolecular spaces. When you mix sugar or salt into water, you make a solution. Seawater is an example of a natural solution.
When the substance is mixed with water (solvent), the molecules of the substances get separated from each other. Then these isolated molecules of the solid material, 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 a 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 unique types of liquids wherein two immiscible liquids are virtually mixed up. One of the liquid is evenly distributed as globules into the another.
In nature, we can see such emulsions in the form of butter. Even when our hand has oil, washing with soap removes it entirely. This is because soap allows water to form an emulsion with oil on the hand and thereby slips away from the skin surface.
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 on the other, it is vice-versa.
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 wherein solid particles are suspended in a solvent.
These suspensions have fine particle matter dispersed evenly within a solvent. These are less common in nature around. But they are widely used by humans in medical 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 carries 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. Nowadays, nano-particle based suspensions are also made. These do not settle down at the bottom as much as those suspensions with bigger particle size.
Aerated solutions: These are also less common to be found 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. Also to make a solution, good amount of work is involved to disperse solids particles into the liquid. But, for these, just passing gas into a liquid is sufficient.