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Determine How the Concentration of a Salt Solution Affects the Rate of Osmosis

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Author: Janice VanCleave

What You Need to Know

A solution is a liquid containing dissolved substances. The liquid part is called a solvent and the dissolved part is called the solute. The concentration of a solution is the amount of dissolved solute in a solvent. Dissolving is the process of the solute breaking apart and thoroughly mixing with the solvent. Osmosis is the movement of water through a membrane (a thin bendable sheet of material) from an area of low solute concentration to an area of high solute concentration.

How Does Osmosis Work?

To understand how osmosis works, it helps to think of the individual particles in a solution, such as a mixture of water (the solvent) and salt (the solute). A solution that contains very few dissolved salt particles has a low salt (solute) concentration. This means that most of the solution is water. The opposite is true if the solution contains many dissolved salt particles.

How Does Osmosis Work?

If vegetables, such as slices of celery, are placed in a bowl of plain water, they become plumper and crisper. This is because water moves into the celery cells due to osmosis. The water moves through the membrane surrounding the celery cells from the side with the lowest salt concentration (plain water) to the side with the higher salt concentration (the solution inside the celery cells). With an increased amount of water in the celery's cells, the celery pieces become crisper, meaning they are firmer. This firmness of the cell resulting from pressure of its contents on the cell membrane is called turgor.

What Does This Have to Do with the Rate of Osmosis?

The rate of osmosis is a measure of the amount of water that moves through a membrane in a certain amount of time.

Real-Life Science Challenge

Reverse osmosis is the opposite of osmosis. This means that water is forced to move from a solution of high solute concentration through a membrane to a solution of low solute concentration. This separates water from the solute, which is left behind. Reverse osmosis is used to remove water during the process of changing maple sap (a watery solution in plants with dissolved nutrients) to maple syrup. Another use of reverse osmosis is to remove water from dissolved impurities.

Fun Fact

Slugs are pests for any gardener. They eat a wide variety of plants, causing anything from slight damage to the death of the plant. The cells of slugs, like all living cells, are surrounded by a membrane. If salt touches a slug, the salt dissolves in the water that lies on the animal's skin. This results in a higher salt concentration outside the slug than inside. Water quickly leaves the cells, resulting in the slug appearing to melt. If enough water is lost, the slug will die. While salt will kill slugs, it can also kill plants. Other methods of controlling slugs include placing barriers around plants that slugs do not like to cross, such as eggshells and sawdust.

Experiment

Now, start experimenting with osmosis.

Hints

  • Make solutions with different salt concentrations.
  • Determine a method of testing turgor pressure.
  • Observe the amount of turgor pressure in a plant, such as celery, at different times, to determine the rate of osmosis.
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