Osmotic Pressure Calculator

Calculate osmotic pressure of solutions using the colligative property formula π = iMRT

Van't Hoff Equation: π = iMRT

R = 0.08206

Example Solutions:

1 for non-electrolytes, 2 for NaCl, 3 for CaCl₂, etc.

298 K = 25°C (room temperature), 310 K = 37°C (body temperature)

Understanding Osmotic Pressure

π = iMRT

  • π = osmotic pressure (atm)
  • i = Van't Hoff factor (number of particles from dissociation)
  • M = molarity (mol/L)
  • R = gas constant = 0.08206 L·atm/(mol·K)
  • T = absolute temperature (K)

Key Concept: Osmotic pressure is the minimum pressure needed to prevent water from flowing through a semipermeable membrane from a dilute solution to a concentrated one.

Understanding Osmotic Pressure

Osmotic pressure is a colligative property that depends on the concentration of solute particles in a solution, not on their identity. It's the pressure required to prevent the flow of solvent molecules through a semipermeable membrane from a region of lower solute concentration to one of higher solute concentration.

The Osmotic Pressure Formula

π = iMRT

Van't Hoff equation for osmotic pressure

π = Osmotic pressure (atm)

The pressure required to stop osmosis

i = Van't Hoff factor

Number of particles per formula unit (1 for non-electrolytes, 2 for NaCl, 3 for CaCl₂)

M = Molarity (mol/L)

Molar concentration of the solute

R = Gas constant = 0.08206 L·atm/(mol·K)

Universal gas constant

T = Temperature (K)

Absolute temperature (°C + 273.15)

Common Van't Hoff Factors

Non-electrolytes

  • • Glucose: i = 1
  • • Sucrose: i = 1
  • • Urea: i = 1

Electrolytes

  • • NaCl: i ≈ 2
  • • CaCl₂: i ≈ 3
  • • Al₂(SO₄)₃: i ≈ 5

Note: Actual i values may be slightly lower due to ion pairing in solution

Practical Example

0.1 M Glucose Solution at 25°C

  • M = 0.1 mol/L
  • i = 1 (non-electrolyte)
  • T = 298.15 K
  • R = 0.08206 L·atm/(mol·K)

π = 1 × 0.1 × 0.08206 × 298.15
π = 2.447 atm

This is approximately 247.9 kPa or 1859 mmHg

Key Concepts

🧬 Colligative Property

Depends only on particle count, not particle type

💧 Semipermeable Membrane

Allows solvent but not solute molecules to pass

⚖️ Equilibrium

Osmotic pressure balances concentration gradient

🌡️ Temperature Effect

Higher temperature increases osmotic pressure

Applications

  • 🧬
    Biological Systems: Cell membranes maintain osmotic balance; red blood cells in different solutions
  • 💧
    Water Purification: Reverse osmosis for desalination and water treatment
  • 💊
    Medical Applications: IV fluid formulation, dialysis, drug delivery
  • 🔬
    Molecular Weight Determination: Calculate molar mass of large molecules like proteins and polymers
  • 🌱
    Plant Biology: Water uptake by roots, turgor pressure in cells
  • 🍬
    Food Industry: Preserving foods with high sugar/salt concentrations

💧Quick Reference

Units:

atm, kPa, mmHg

Formula:

π = iMRT

Constant:

R = 0.08206 L·atm/(mol·K)

Property:

Colligative (particle-dependent)

Level:

College Chemistry

🔗Related Calculators

📐Related Formulas

🎯Where It's Used

  • 🧬

    Cell Biology

    Osmotic balance in cells

  • 💧

    Water Treatment

    Reverse osmosis systems

  • 💊

    Medicine

    IV solutions and dialysis

  • 🔬

    Research

    Molecular weight determination