Osmotic Pressure - Online Tutor, Practice Problems & Exam Prep

Osmotic pressure is a crucial concept in understanding the movement of water across a semipermeable membrane, where water naturally flows from areas of lower solute concentration to areas of higher solute concentration. This pressure is determined by the concentration of the solution and the temperature. The formula for calculating osmotic pressure (π) is:

$\pi =iMRT$

where 'i' represents the Van't Hoff factor, 'M' is the molarity (moles per liter), 'R' is the gas constant (0.08206 L·atm/mol·K), and 'T' is the temperature in Kelvin. A higher concentration or temperature will result in a greater osmotic pressure, influencing the rate and direction of water movement in systems such as living cells or industrial processes.

Osmotic Pressure Concept 1

Now recall that osmotic pressure is the force that drives the movement of water from a lower concentration to a higher concentration. And remember that the osmotic pressure of a solution can be influenced by its concentration and temperature.

So if we take a look here, we have our osmotic pressure formula. Here we're going to say that osmotic pressure, which is represented by this Pi looking symbol, is in units of atmospheres and it equals I, which is your Van Hoff factor, capital M, which is your molarity or concentration or solubility, OK. And that will be in moles per liter. So moles of solute over liters of solution times RR is your gas constant which is 0.08206 liters times atmospheres over moles times K.

And then here finally T is our temperature and that would be in units of Kelvin. Just remember, when it comes to our osmotic pressure, concentration and temperature can play a role in influencing the osmotic pressure of any solution.

Osmotic Pressure Example 1

Here it says calculate the osmotic pressure of a solution. That is 18.30 milligrams of zinc oxide in 15.1 M LS of solution at 26°C. All right, so osmotic pressure equals I×molarity×R×T. Zinc oxide is an ionic solute that breaks up into zinc ion and oxide ion. That's two ions, so I=2.

Capital M is our molarity, which is moles over liters here. When I convert the 15 M LS into liters, that's oh .015 liters. Then I can change the 8.30 milligrams of zinc into moles. So remember, 1 milligram is 10⁻3 grams and one mole of zinc the weight of zinc oxide. The mole, the weight of zinc oxide, when we figure that out is, well, the mass is 81.38 grams. So when we work that out, the moles is 2.2487×10⁻4 moles.

So then that's going to give us our moles of our liters. R is our gas constant, which we don't have to do anything, we just have to plug it in and then our temperature needs to be in Kelvin. So add 273.15 to this number here and that gives us 299.15 Kelvin. So then what cancels out? Kelvin's cancel out? Moles cancel out, liters cancel out, and we're left with atmospheres at the end.

When we plug this in, we're going to get as our atmospheres 0.731 atmospheres at the osmotic pressure for this given solution.

The osmotic pressure of blood is 5950.8 mmHg at 41°C. What mass of glucose, C₆H₁₂O₆, is needed to prepare 5.51 L of solution. The osmotic pressure of the glucose solution is equal to the osmotic pressure of blood.

• A. 54.7 g
• B. 0.304 g
• C. 419 g
• D. 302 g

The osmotic pressure of a solution containing 7.0 g of insulin per liter is 23 torr at 25ºC. What is the molar mass of insulin? (1 atm = 760 torr)

• A.  474.5 g/mol
• B. 6 x 103 g/mol
• C. 5.2 x 103 g/mol
• D. 5.7 x 103 g/mol

Here’s what students ask on this topic:

What is osmotic pressure?

Osmotic pressure is a fundamental concept in chemistry and biology related to the movement of solvent molecules through a semipermeable membrane. This membrane allows certain molecules or ions to pass through it by diffusion and occasionally by more specialized processes of facilitated diffusion, active transport, or passive transport.

In the context of osmotic pressure, the solvent (often water) moves from a region of lower solute concentration to a region of higher solute concentration. The "pressure" aspect refers to the potential pressure exerted by the solvent if it were allowed to flow freely into the solute-containing region. This pressure is necessary to stop the flow of solvent molecules through the membrane.

Osmotic pressure can be calculated using the formula:

$\pi =iMRT$

where $\pi$ is the osmotic pressure, $i$ is the van 't Hoff factor (which indicates the number of particles the solute dissociates into), $M$ is the molarity of the solution, $R$ is the ideal gas constant, and $T$ is the temperature in Kelvin. This principle is critical in many biological and chemical processes, including the maintenance of proper cell function and the behavior of fluids in living organisms.

How do you calculate osmotic pressure?

Osmotic pressure can be calculated using the formula derived from van't Hoff's law for dilute solutions, which is:

$\Pi =iMRT$

where:

• $\Pi$ (pi) represents the osmotic pressure,
• $i$ is the van't Hoff factor, which indicates the number of particles the solute dissociates into in solution,
• $M$ is the molarity of the solution, which is the number of moles of solute per liter of solution,
• $R$ is the ideal gas constant (0.0821 L·atm/mol·K), and
• $T$ is the temperature in Kelvin.

To calculate osmotic pressure, follow these steps:

1. Determine the molarity ($M$) of the solute in the solution.
2. Identify the van't Hoff factor ($i$) for the solute (for non-electrolytes, $i$ = 1; for electrolytes, it's equal to the number of ions formed per molecule).
3. Measure the temperature ($T$) in Kelvin. If you have the temperature in Celsius, convert it to Kelvin by adding 273.15.
4. Use the ideal gas constant ($R$) value that matches the units of pressure you want for $\Pi$.
5. Plug these values into the formula $\Pi =iMRT$ and solve for the osmotic pressure.