Water Adsorption Through Molecular Sieve Beads

When trying to separate ethanol from water, distillation only creates 190 proof (95% ethanol with 5% water). By adding small molecular sieve beads to the solution, 200 proof (100% ethanol) can be achieved. The molecular sieve beads work by adsorbing the water. The size of the water and ethanol molecules is the key to the success of the sieve beads. Water as a molecule is much smaller than ethanol, so it can successfully fit through the pores of the sieve beads.

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Shenandoah

Iowa Core Standard

HS-PS2-6

Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.*

Driving Question

How do the sieve beads work to separate the water from the ethanol?

Probing Questions

How long does it take the beads to work?
Does the ratio of beads to solution affect the time? If so, what is the optimal ratio?
Why can ethanol only get to 95% without the use of the beads?
Why is it necessary to get that last 5%?
How do you determine what percent alcohol is present?
Are there other materials that selectively adsorb different materials like these beads?

Classroom Suggestions

Students could:

Conduct an experiment with actual sieve beads recording how long it takes for the water to separate from isopropyl alcohol.
Change the quantity of sieve beads in the solution and record how it affects the time needed to separate the water from the isopropyl alcohol.

Resources

Tartan Academy | How Do Molecular Sieves Work?: A video showing how sieve beads work at a molecular level.

Contributors

Submitted by Jill Isaacson.