Osmosis is defined as the flow of water through a membrane through which only water can flow. It works with the presence of a semipermeable membrane through which solute and particles are held back and only water is allowed to pass. The water shows movement from a field of high concentration to a field of low concentration. It is a spontaneous phenomenon that allows the flow of the solvent molecules with the existence of a semipermeable membrane from a solvent of a pure kind to the solution or from a dilute solution to a concentrated solution. This observation was first made by Abbe Nollet.
There are some natural semipermeable membranes, for example, animal bladder, cell membrane, etc. An artificial semipermeable membrane CU2[Fe (CN)6] is one that does not work in non-aqueous solutions at all. This is because it has shown to dissolve in them.
Types of osmosis
There are two types of osmosis that take place:
- Exosmosis: The phenomenon which shows the flow of water or a given solvent in an outward direction from a cell through a semipermeable membrane.
- Endosmosis: The phenomenon which shows the flow of water or a given solvent in an inward direction from a cell through a semipermeable membrane.
In order to counter the osmotic flow, a certain pressure of a kind must be put or applied to the solution. This must be done so in order to prevent the solvent of pure nature from flowing through the semipermeable membrane which has been separating the two liquids; this is known as the osmotic pressure. This pressure does not sustain osmosis but in turn, counters it.
The pressure of osmosis can be found out by using the formula:
π = iCRT,
π = osmotic pressure
i = van’t Hoff factor
C = molar concentration of the solute in the solution
R = universal gas constant
T = set temperature
Jacobus van’t Hoff was a Dutch chemist who put forth the relationship between the osmotic pressure of a solution and the molar concentration of its solute. Please keep in mind that the question to calculate osmotic pressure only works for a solution that behaves like an ideal solution. It has been observed and proved that the solvent molecules show to move through the semipermeable membrane into the solution side until the osmotic pressure (of the solution) is applied to the solution side. You must be wondering, what might happen if we apply a higher pressure than the osmotic pressure towards the solution side. The answer is, that in such a situation, a process called reverse osmosis takes place.
What is reverse osmosis?
A phenomenon in which the pure solvent passes through the semipermeable membrane in order to gather in a separate area when a pressure that is greater than the osmotic pressure is applied to the solution side.
A homogenous mixture of both a solute and a solvent defines a solution. Different properties are present in a solution, apart from the solvent and the solute molecules that compose them. Colligative properties are those that are dependent not on the number of dissolved solute molecules, irrespective of what the solute is.
What’s the reason behind plants keeping their upright shape? This is because of the presence of osmotic pressure. When adequate amounts of water are provided to plants, the cells tend to expand once they have absorbed the water. The cells increase their expansion and a certain kind of force is exerted on their walls which allows them to stand up straight. It is a similar reason as to why plants droop down when they are not supplied with adequate amounts of water as well. The molecular weights of compounds can be determined by using the measurement of osmotic pressure. Reverse osmosis is used when it comes to the purification and distillation of seawater.
Hypothetically, let’s Imagine the process of osmosis happening in an upright U- tube. The solution’s height will proceed to boost up due to a net flow of solvent. This will happen until the added pressure of the height will allow the movement of the solution to succumb and come to halt. The height difference which exists between the two sides can be changed into pressure. After which we can find the osmotic pressure which has been exerted on the solution by the solvent of a pure kind.
Another way to explain Osmotic pressure is as the pressure which is mandatory to nullify osmosis. Yes, a possible way to curb osmosis is to boost up the hydrostatic pressure on the solution side of the membrane. This will squeeze out the solvent molecules and bring them closer together, which in turn will increase their “escaping tendency.” The escaping tendency of the solution can be increased until it has come to a point to be equal to that of the molecules in the pure solvent. This is when osmosis will come to halt. Thus, it can be said that the osmotic pressure is the pressure that is compulsory to achieve osmotic equilibrium.
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