Distributed Block - View: Magazine: Latest Cover

cover of Nov. 28, 2015 Science News

Eureka! Lab

A place for discovery 
Bethany Brookshire

Eureka! Lab

Scientists Say: Osmosis

This word describes how liquids can move across membranes to equalize the amount of a substance dissolved in them

Eureka! Lab

On the left, there are few molecules per volume of solution; on the right are many more. A somewhat porous membrane separates them. If microscopic holes in the membrane are big enough (but not too big), the liquid will move from left to right — through that membrane. And it will continue to do that until the concentration of the particles per unit volume is equal in the solution on each side of the membrane.  

OpenStax College/Wikimedia Commons (CC BY 3.0)

Osmosis (noun, “Oz-MO-sis”)

The movement of a solution across a membrane — a barrier that blocks the flow of some, but not all, materials. The liquid in the solution will move from the side with fewer dissolved molecules toward the side with more. Movement will continue until the concentrations on both sides of the membrane are the same. Think of a solution low in water and high in salt next to a solution high in water and low in salt. The water will move from the high-water, low-salt solution toward the low-water, high-salt solution. The water will continue this flow until the concentration of salt in each solution is equal.

In a sentence

To get to Mars, astronauts may have to depend on osmosis to purify their pee — so they can drink it again.

Follow Eureka! Lab on Twitter

Power Words

(for more about Power Words, click here)

concentration  (in chemistry) A measurement of how much of one substance has been dissolved into another.

dissolve  To turn a solid into a liquid and disperse it into that starting liquid. For instance, sugar or salt crystals (solids) will dissolve into water. Now the crystals are gone and the solution is a fully dispersed mix of the liquid form of the sugar or salt in water

membrane  A barrier which blocks the passage (or flow through of) some materials depending on their size or other features. Membranes are an integral part of filtration systems. Many serve that function on cells or organs of a body.

osmosis   The movement of certain molecules within a solution across a membrane. The movement is always from the solution where the concentration of some chemical is higher to the solution where the concentration of that chemical is lower. This movement tends to continue until concentrations on each side of the membrane are the same.

permeable  Having pores or openings that permit liquids or gases to pass through. Sometimes materials can be permeable for one particular type of liquid or gas (water, for example) but block others (such as oil).

semi-   An adjective meaning “somewhat.”

solution   A liquid in which one chemical has been dissolved into another.

solute  A substance dissolved in another substance, forming a solution.

solvent  A material (usually a liquid) used to dissolve some other material into a solution.

Readability Score: 
By Bethany Brookshire 7:00am, November 19, 2015
American Chemical Society
Students love to see colorful fires in chemistry class. But a popular flaming-salts demo has resulted in some horrible injuries. Several groups warn of its dangers and propose a far safer version.
By Bethany Brookshire 7:00am, November 16, 2015
carbon dioxide
Carbon dioxide, sulfur dioxide and zirconium dioxide all have something in common. They are all molecules with two oxygens bound to some other element.
By Bethany Brookshire 7:00am, November 9, 2015
When brain cells need to communicate, they use chemicals as messengers. These molecules have a special name.
By Bethany Brookshire 7:00am, November 6, 2015
candy bar float
tir salt into water and make a candy bar float. Sure, it’s fun — but you can also make it research. You just need a big bag of candy and some measurements to turn this demo into an experiment with density.
By Bethany Brookshire 7:00am, November 2, 2015
mossy log
These days you might think organic refers just to food. But it has a completely different meaning in chemistry.
By Bethany Brookshire 7:00am, October 26, 2015
A quartile might sound like a fourth. But that’s not quite what it is.
By Bethany Brookshire 7:00am, October 22, 2015
Max Du
Many popular drinks contain caffeine — a stimulant that in high amounts can keep you up at night. One teen is now measuring just how much is in the beverages we drink.
By Bethany Brookshire 7:00am, October 19, 2015
jet stream
You might hear about the jet stream on a weather report, but what is it? We explain.
By Bethany Brookshire 7:00am, October 16, 2015
milk and cookie
One teen was dismayed to learn milk might host harmful pollutants. This prompted him to use his science fair project as a way to find out just what was in his favorite drink.
By Bethany Brookshire 7:00am, October 14, 2015
cookie butter
I teamed up with the ACS Reactions team to make a video about cookie science. Here are the details of our experiment.
Subscribe to RSS - Eureka! Lab

From the SSP Newsroom

Science News


Science News for Students


Eureka! Lab