What is Osmotic Pressure?
Osmotic pressure is a minimum pressure that is supposed to be applied to a solution to halt the incoming flow of its pure solvent across a semipermeable membrane (osmosis). It is basically a colligative property and is purely dependent on the concentration of solute particles of the solution.
Osmotic Pressure Equation
Jacobus, a Dutch chemist, found a quantitative relationship between the osmotic pressure and solute concentration, expressing the following as an Osmotic Pressure equation.
π=iCRT.
Where,
‘π’ is the osmotic pressure
i is dimensionless van ‘t Hoff index
c is the molecular concentration of solute in the solution
R is the ideal gas constant
T is the temperature in kelvins
Furthermore, it is essential to note that the derived Osmotic Pressure equation holds only true for solutions that behave the same as ideal solutions. Osmotic pressure of pure water is 0 because it has 0 osmotic pressure.
What Exactly is Osmosis?
The minimal pressure required for a solution to stop the passage of solvent molecules through a semipermeable membrane is known as the osmotic pressure. The passage of solvent molecules through a membrane from a low-concentration segment to a high-concentration segment is referred to as the osmosis process. The two sides of the semipermeable membrane eventually achieve equilibrium due to this process.
The semipermeable membrane is a type of membrane that allows solvent molecules to pass through while preventing solute particles from passing through. This osmosis process will come to a halt if we apply enough pressure to the solution side of the semipermeable membrane.
The osmotic pressure is defined as the minimal amount of pressure required to stop the osmosis process. This method will be repeated until the concentrations of the two solutions are equal. It could also happen if the increased pressure prevents any additional water from passing through the membrane.
Understanding the Osmotic Pressure
Consider a U-Tube showing an osmotic pressure diagram below which is known as the Osmotic Pressure diagram.
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The left side of the U-tube contains an aqueous solution, and the right side is of pure water. Here, the pure water is trying to dilute the solution by passing through the semipermeable membrane. Eventually, the weight added of the excess water on the left tube causes enough pressure to halt osmosis.
As we discussed, the Osmotic pressure is the one that needs to be applied to a solution to prevent an inward solution to prevent the inward flow of water across a semipermeable membrane. It is also explained as the pressure required to nullify osmosis. One of the ways to stop osmosis is to increase the hydrostatic pressure on the solution side of the membrane. This ultimately squeezes the solvent molecules together closer, increasing their “escaping tendency.” Whereas, the escaping tendency of a solution can be raised until it becomes equal to the molecules in the pure solvent. And at this point, osmosis will cease. Osmotic pressure is the one required to achieve osmotic equilibrium.
Osmotic Pressure Example
How much glucose (C6H12O6) per liter should we use for an intravenous solution to match the 7.65 atm at 37 degrees Celsius osmotic pressure of blood?
Explanation:
The Osmotic Pressure calculation example is given with a brief description below.
Osmotic pressure is a colligative substance property because it depends on the concentration of the solute but not its chemical nature.
Calculating the osmotic pressure formula chemistry is done using, π =iMRT
Step 1: Determining the van ‘t Hoff factor.
Because glucose doesn’t dissociate into ions in the solution, the van ‘t Hoff factor is 1
Step 2: Finding the absolute temperature.
T = Celsius Degrees + 273
T = 37 + 273
T = 310 Kelvin
Step 3: Finding the concentration of glucose.
Π = iMRT
M = Π/iRT
M = 7.65 atm / (1) (0.0820 L.atm/mol.K) (310)
M = 0.301 mol / L
Step 4: Finding the amount of sucrose per liter.
M = mol/Volume
Mol = M·Volume
Mol = 0.301 mol/L x 1 L
Mol = 0.301 mol
Considering the periodic table,
C = 12 g/mol
H = 1 g/mol
O = 16 g/mol
Molar of the glucose = 6(12) + 12(1) + 6(16)
Molar mass of the glucose = 72 + 12 + 96
Molar mass of the glucose = 180 gm/mol
Mass of the glucose = 0.301 mol x 180 gm/1 mol
Mass of the glucose = 54.1 grams
Answer:
Finally, we should use 54.1 grams per liter of glucose for an intravenous solution to match the 7.65 atm at 37 degrees Celsius osmotic pressure of blood.
What Happens if a Pressure of Higher Magnitude than the Osmotic Pressure applied to the Solution Side?
In this case, the solvent molecules would start moving through the semipermeable membrane from the solution side (the point at the solute concentration is high) to the solvent side (the point at the solute concentration is low). This method is known as reverse osmosis.
Examples and Instances
Plants rely on osmotic pressure to keep their upright structure, also referred to as turgidity. When the plant receives enough water, its cells absorb the water and expand thus becoming turgid and they hold the shape of the various parts firmly. When the cells expand by absorbing water, it ultimately increases the pressure on their cell walls.
When a plant receives insufficient water, its cells become hypertonic and they shrink due to water loss. They wilt and lose their solid, erect posture, a situation known as flaccidity.
Desalination and purification of saltwater, which requires reverse osmosis, is another notable application of osmotic pressure.
Our fingers become wrinkly when we sit in the bathtub or submerge them in water for an extended period of time. This is due to osmosis as well. Our fingers' skin absorbs water and expands or bloats, resulting in pruned or wrinkled fingers.
Slugs and snails are killed by sprinkling salt on them. It involves the osmosis process, which kills them. They end up shedding water as the liquid inside them tries to dilute the salt concentration and preserve the mucus layer. Slugs and snails will dry up and die if they are exposed to too much salt
Osmotic Pressure Example on Wilting Plants
The Osmotic Pressure example considering the plants can be given in a brief way. Most of the plants use osmotic pressure to maintain the shape of their stems and leaves.
If we have kept potted plants, we probably know that our plants can become very wilted very quickly if they are not watered for a long time. But just within minutes of watering, they can perk them right back up!
This happens because the stem and leaves of many plants are fundamentally "inflated" by osmotic pressure – the salts in the cells cause water to be drawn in through osmosis, making the cell plump and firm.
If enough water is not available, the plant will wilt because its cells become "deflated." In scientific terms, they are "hypertonic," which means "the concentration of solute is too high."
Plants can also evidence the power of osmotic pressure as they grow.
We may have seen plants springing up through asphalt, or tree roots growing through concrete or bricks.
Possibly, this, too, is made by osmotic pressure: as plants grow, their cells draw in more water. The slow but inexorable pressure of water moving through the plant cell's membranes can actually push through asphalt!
FAQs on Osmotic Pressure
1. Is Osmosis a Reason for Cholera?
Osmosis allows for terrible things to happen. Without osmosis, cholera would not be possible. The bacteria of choleric populate in our intestines and begin to reverse the intestinal cells' ionic orientation. In different terms, it changes the way ions and, subsequently, water transport in our intestines. As a result, cholera performs a perfect coup.
Firstly, when our ions' orientations are switched, the intestinal cells are no longer able to do water absorption into the body. Now osmosis happens in another direction, and water moves from our intestinal cells into our intestines. This causes cholera's infamously deadly watery diarrhea. Secondly, this compounds the rate at which you become dehydrated. Not only you cannot absorb water, but also you are literally being drained dry. Resultantly cholera can kill you much quicker because it doesn't rely on how much water you consume.
2. Explain about Osmotic in Terms of Water Potential
Water potential is the measure of pressure, ionization, molar concentration, and temperature on one side of a semi-permeable membrane. Comparing the water potential inside a cell to that of outside a cell, the direction of osmosis can be determined.
There is a simple model to represent the relationship between water potential in a cell and the water potential of a cell's extracellular environment.
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Water potential is a quantitative measure of one side pressure of a membrane. By comparing the water potential inside a cell or tissue, with the water potential outside a cell or tissue, the direction of osmosis can be determined.
The symbol for water potential is psi for Poseidon (ψ), which is called the Greek god of the water.
3. How is water purification done using osmotic pressure?
Reverse osmosis removes salt from seawater to produce fresh water. Filtering, also known as "reverse osmosis," is a typical water purification method. It is based on osmotic pressure. The cleansed water is placed in a chamber under a more immense pressure than the osmotic pressure exerted by the water and the solutes dissolved in it. A variably permeable membrane in one half of the chamber allows water molecules to pass through but not solute particles.
4. How can osmosis be applied to preserve food?
Fruits are preserved using sugar. Fruits are commonly preserved in honey to keep them from spoiling. Sugar is commonly used in jams and jellies made from fruits nowadays, and it serves as a preservative. Jellies are transparent liquids produced from fruit juice or fruit extract. Because sugar creates a hypertonic solution, it sucks water out of food, making it unavailable to bacteria. Microbial metabolism is halted, and they die due to water loss.
5. How is osmotic pressure a colligative property?
The osmotic pressure is the lowest excess pressure that must be provided to prevent the solvent from entering the solution through the semipermeable barrier. The colligative property of a solution is determined by the number of solute particles present, regardless of their nature, in relation to the total number of particles in the solution. The number of particles in a solution, or the molarity of the solution, determines the osmotic pressure. As a result, osmotic pressure is a colligative property.
6. What reasons can cause the osmotic pressure to change?
Solute concentration and temperature are two elements that influence osmotic pressure.
The number of solute particles that are present in a unit volume of a solution actually determine the solution's potential osmotic pressure. Solute concentration is directly proportional to the osmotic pressure. Any change in the temperature whether rising or falling affects the osmotic pressure directly.
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7. How is osmotic pressure different from osmotic potential?
Osmotic pressure is the hydrostatic pressure that balances and inhibits the osmotic influx of water into a concentrated solution. The ability of a solution to promote water movement into it through a partially permeable barrier as a result of dissolved solutes is known as osmotic potential.
In a closed system, osmotic pressure develops, and the result is positive. On the other hand, the osmotic potential can occur in both open and closed systems, and the resultant value is negative.
