Osmotic pressure difference,pressure and electrical potential difference.

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SUMMARY

The discussion focuses on calculating osmotic pressure differences and electrical potential differences in hydrogel samples in equilibrium with sodium chloride solutions. For a hydrogel with a fixed charge density of -0.2 moleq/l at 298 K, the osmotic pressure difference is determined to be 80 kPa, and the effective stress in the sample is also 80 kPa. In a separate scenario with a hydrogel at 300 K and a fixed charge density of -0.05 moleq/l, the pressure in the sample is calculated to be 10 kPa, with an electrical potential difference of -4.3 mV.

PREREQUISITES
  • Understanding of osmotic pressure calculations
  • Knowledge of Donnan equilibrium principles
  • Familiarity with linear elastic material properties
  • Basic concepts of electrical potential difference in ionic solutions
NEXT STEPS
  • Study the principles of osmotic pressure and its calculation methods
  • Research Donnan equilibrium and its applications in hydrogel systems
  • Explore linear elasticity in materials science
  • Learn about electrical potential differences in ionic solutions and their implications
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Students preparing for exams in materials science, chemical engineering, or related fields, particularly those focusing on hydrogel behavior in ionic solutions.

KloosterG
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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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Anybody how can help me before my exam tomorrow?
 

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