Lab 2: Osmolarity, Tonicity, and Osmosis

Osmolarity

The concentration of solute particles in a solution, specifically non-penetrating solutes, expressed in osmoles per liter (Osm/L).

Tonicity

The effect of a solution on the volume of a cell, considering both penetrating and non-penetrating solutes.

Isotonic

A solution with the same osmolarity as the intracellular fluid of erythrocytes, resulting in no net movement of water.

Hypotonic

A solution with lower osmolarity than the intracellular fluid, causing water to move into the cell and swell it.

Hypertonic

A solution with higher osmolarity than the intracellular fluid, causing water to move out of the cell and shrink it.

Osmosis

The movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration.

Penetrating solutes

Solutes that can cross the cell membrane and do not directly affect tonicity.

Non-penetrating solutes

Solutes that cannot pass through the membrane and contribute to the osmolarity of the solution, affecting water movement.

Hemolysis

The bursting of red blood cells typically caused by a hypotonic solution.

Crenation

The shrinking of red blood cells occurring when placed in a hypertonic solution.

Hypo-osmotic

A solution with lower osmolarity than the intracellular fluid of erythrocytes.

Iso-osmotic

A solution with the same osmolarity as the intracellular fluid of erythrocytes.

Hyper-osmotic

A solution with higher osmolarity than the intracellular fluid of erythrocytes.

Osmolarity Calculation

Osmolarity = Molarity × Number of particles in solution.

Glucose

A penetrating solute that does not dissociate; 1 M glucose solution has an osmolarity of 1 Osm/L.

NaCl

A non-penetrating solute that dissociates into two ions (Na⁺ and Cl⁻), making its osmolarity for a 1 M solution equal to 2 Osm/L.

Percent solution

A concentration expressed as the number of grams of solute per 100 mL of solution.

Molarity from percent solution

Molarity can be calculated using the formula: Molarity (M) = (Percent solution × 10) / Molecular weight of the solute.

Example of calculating molarity

To find the molarity of a 10% NaCl solution, divide 10 g by the molecular weight of NaCl (58.44 g/mol) and multiply by 10.

Iso-osmotic vs. Isotonic

Iso-osmotic solutions have the same osmolarity but may not exert the same tonicity effect on cells.

Osmolarity in clinical settings

Osmolarity is crucial for preparing IV solutions to prevent cellular damage or excessive swelling.