Osmotic pressure difference,pressure and electrical potential difference.

In summary, the conversation is about an upcoming exam for a course the speaker is not familiar with. They have studied the material and attempted practice questions, but are having trouble with the following two questions:Q1: Calculating the osmotic pressure difference and effective stress in a hydrogel sample in equilibrium with a sodium chloride solution.Q2: Finding the pressure and electrical potential difference in a cylindrical hydrogel sample in equilibrium with a sodium chloride solution.The speaker has attempted to solve these questions using Donnan-equilibrium concentrations, but is unsure if they are on the right track. They are seeking help before their exam tomorrow.
  • #1
KloosterG
2
0
I have an exam on monday, for a course I'm not familiar with. I have studied the material and tried some example exam question but I can't seem to figure out how to get to the result of the following questions.
Q1:

Homework Statement


A sample of hydrogel is in equilibrium with a sodium chloride solution of 0.3 moles/l at T=298 K. The fixed charge density of the sample is −0.2 moleq/l.
a. Calculate the osmotic pressure difference between the sample and the solution.
80 kPa
b. Calculate the effective stress in the sample.
80 kPa

The Attempt at a Solution


I tried it by calculating the Donnan-equilibrium concentrations but I have a feeling that's the wrong direction.

Q2:
A cylindrical hydrogel has homogenous, isotropic lineair elastic material properties. The sample is in equilibrium with a sodium chloride solution of concentration 0.15 Mol/l and of pressure zero, and is at temperature T= 300 K. The fixed charge density of the sample is −0.05 moleq/l.
a. What is the pressure in the sample?
10 kPa
b.What is the electrical potential difference between the sample and the solution?
ξ = −4.3mV

a. I started again with calculating the Donnan-equilibrium concentrations, but got stuck after that.
b. No idea where to start.

Thank in advance for anyone willing to help.
 
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  • #2
Anybody how can help me before my exam tomorrow?
 

1. What is osmotic pressure difference?

Osmotic pressure difference is the difference in pressure between two solutions separated by a semipermeable membrane. It is caused by the movement of solvent molecules from a region of lower solute concentration to a region of higher solute concentration.

2. How is osmotic pressure difference measured?

Osmotic pressure difference is typically measured in units of pressure, such as atmospheres or pascals. It can be calculated using the van't Hoff equation, which takes into account the concentration of solutes and the temperature of the solutions.

3. What role does osmotic pressure difference play in biological systems?

In biological systems, osmotic pressure difference is important for maintaining the balance of fluids and electrolytes in cells and tissues. It also plays a role in processes such as osmoregulation and the movement of nutrients and waste products across cell membranes.

4. How does osmotic pressure difference differ from pressure?

Osmotic pressure difference specifically refers to the pressure caused by the movement of solvent molecules across a semipermeable membrane. Pressure, on the other hand, can refer to any force applied to a surface. Osmotic pressure difference is a type of pressure, but not all pressures are osmotic in nature.

5. What is the relationship between osmotic pressure difference and electrical potential difference?

Osmotic pressure difference and electrical potential difference are two different types of energy differences. Osmotic pressure difference is caused by the movement of solvent molecules, while electrical potential difference is caused by the movement of charged particles. In some cases, these two types of energy differences can be linked, such as in the case of electroosmosis where the movement of charged particles is driven by osmotic pressure difference.

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