Salting Out—Density Bottle
Publication No. 12632
Two layers of beads are suspended in the middle of the bottle. Give the bottle a shake and the beads move to opposite ends. The beads then slowly move back to the starting position.
Isopropyl alcohol, reagent, 500 mL*
Sodium chloride, 100 g*
Water, distilled or deionized
Balance, 0.1 g precision
Beads, UV-sensitive, 50 g*
Bottle with cap, plastic, 1-L*
Graduated cylinders, 500-mL, 2
Pony beads, green, 50 g*
*Materials included in kit.
Isopropyl alcohol is a flammable liquid and a fire hazard. It is slightly toxic by ingestion and inhalation. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Follow all laboratory safety guidelines. Please review current Safety Data Sheets for additional safety, handling and disposal information.
The bottle may be reused for many years.
Student Worksheet PDF
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesDeveloping and using models
Obtaining, evaluation, and communicating information
Analyzing and interpreting data
Disciplinary Core IdeasMS-PS1.A: Structure and Properties of Matter
HS-PS1.A: Structure and Properties of Matter
HS-PS2.B: Types of Interactions
Structure and function
Cause and effect
Systems and system models
MS-PS1-1. Develop models to describe the atomic composition of simple molecules and extended structures.
Answers to Questions
a. How can you infer from your diagram which is more dense?
The more dense material will be on the bottom of the bottles. Materials with greater density sink to the bottom.
b. What can you infer about the relative densities of the different colored beads?
The colorless beads are less dense than the green beads because they are floating on top of the green beads. There is no mixing between the different colored beads indicating that the beads have different densities.
When the bottle is shaken, the beads will be all mixed up. After being set down, the beads will then quickly sort back into the colorless layer and green layer.
When the bottle was shaken, the isopropyl alcohol and sodium chloride solution mixed completely, making a homogenous soluion of uniform density. The density of the solution was greater than the density of the colorless beads, so those beads floated on top. The density of the solution was less than the density of the green beads, so the green beads sank. As the bottle sat undisturbed, the isopropyl alcohol and sodium chloride solution separated, with the isopropyl alcohol on top, then the colorless beads and green beads, and the sodium chloride solution on bottom.
Water and isopropyl alcohol are miscible liquids that form strong hydrogen bonds. When sodium chloride is added to the solution, the ionic solid dissociates. The ions attract the water molecules and disrupt the hydrogen bonds between the water and isopropyl alcohol molecules. As two liquid layers separate, the isopropyl alcohol/water solution will appear on top of the more dense aqueous sodium chloride solution. The phenomenon is known as salting-out and is widely used to separate and purify organic compounds from aqueous mixtures. It is also used to precipitate proteins from aqueous cell extracts.
Special thanks and acknowledgment to Lynn Higgins, ACS Polymer Ambassador, Missouri, in recognition of her creative activity idea that this demonstration is based on.