Salting Out of Ethanol and Water

Purpose:

To introduce or illustrate the concept of intermolecular forces via salting out, or the separation of an organic phase from an aqueous phase by the addition of a salt.

Materials:

• 2 large test tubes with stoppers

Reagents:

• 1M Hydrochloric acid (HCl)
• Bromothymol blue indicator
• Potassium carbonate (KCO_3(s))
• Ethanol (EtOH/CH₃CH₂OH)

Hazards and PPE:

• Hydrochloric acid is acutely corrosive and toxic. Avoid skin contact and inhalation of fumes.
• Wear approved safety goggles and gloves.

Protocol:

Demonstration

1. To the first test tube, add 10mL Ethanol, 10mL DI H₂O, 5 drops bromothymol blue indicator, and 1 drop 1M HCl.
2. Add 3g KCO₃ to the second test tube.
3. Pour the contents of the first test tube into the second. Stopper and shake the tube. The solution should turn blue and separate into two phases: a colorless aqueous and blue organic phase.

Questions to Ask

1. Which phase is water, which is alcohol? Why?
2. Is the separation of water and alcohol complete?
3. Could other liquid pairs or salts be used?
4. Could a dye be found that would wind up in the water-rich phase? Why?

Additional Notes:

• If you are using a large enough beaker and cylinder for a lecture hall (on the order of 1 to 2 liters), it could take quite a while to heat the water (close to an hour). In this case, you should heat the water to almost boiling before the lecture to save time during the lecture. It may also take a few minutes for the pressure difference to be enough to cause the water to be pushed up the cylinder.

Disposal:

• End mixture can be disposed of down the drain with excess water.

Reactions:

• Salting out is a purification method that utilizes the reduced solubility of certain molecules in a solution of very high ionic strength.

Citations:

1. This demo adapted from the demo library of the Chemistry department at the University of Illinois at Urbana-Champaign.

Videos:

• Salting Out Effect of Water and Methyl Alcohol

  FlinnScientific

  While this version of the demonstration uses different glassware, dye instead of pH indicator, and MeOH instead of EtOH, the principle is sound, and this video provides a solid foundation of how to perform the demonstration.