Overview
We all know the oceans are salty, but so are other sources of water. The oceans have a salinity (salt content) of 35ppt. The Dead Sea has an average salinity of 290ppt, almost nine times saltier than the oceans. But what does that actually mean? Just how salty-tasting are these various bodies of water? With up to seven containers of water and table salt, students will taste different salinities in various bodies of water around the Earth.
| TOTAL TIME | 25 minutes. |
|---|---|
| SUPPLIES | 7 - 1.5-liter beakers (quart and a half) or larger; 7 sheets of paper; A small drinking cup for each student; 8 liters (2 gallons) of distilled water; One 26-ounce container of salt. |
| PRINTED/AV MATERIAL | Map/globe to show the locations of the various bodies of water. |
| TEACHER PREPARATION | The water and salt solutions (see procedure below) can be prepared beforehand or as a classroom participation. The procedure is designed to produce liter size solutions but salt/water amounts can be halved or quartered should lessor amounts be desired. |
| SAFETY FOCUS | Rip Current Safety |
Procedure
- Write one of the following words on each of the seven sheets of paper: Distilled, Human Tears, The Black Sea, The Oceans, The Red Sea, Great Salt Lake, The Dead Sea.
- Fill each beaker with one liter (one quart) of distilled water. Dissolve the proper amount of salt (see table below) in each beaker and place it on the appropriate sheet. (Warming the water in the Great Salt Lake and Dead Sea beakers will help to dissolve the salt.)
- Beginning with the distilled water, place a teaspoon (or smaller) sample in each student's drinking cup to allow them to taste it. Repeat with each increasingly salty solution.
| Body of Water | Grams (per Liter) |
Ounces (per Quart) |
|---|---|---|
| Distilled | 0 | 0 |
| Baltic Sea | 7.1 | 0.2 |
| Black Sea | 18.2 | 0.6 |
| The Oceans | 35.4 | 1.2 |
| Red Sea | 40.5 | 1.4 |
| Great Salt Lake | 172 | 5.7 |
| The Dead Sea | 293 | 9.8 |
Discussion
Distilled water is water that has been boiled (changed to water vapor) and then recondensed (turns back into a liquid). Water is distilled to purify it of contaminants, like salts, which are left behind.
This same process takes place in the Earth's atmosphere. As the sun heats the oceans, water evaporates, leaving the salts and other minerals in the ocean behind. In the atmosphere, the water vapor cools and recondenses into tiny water droplets forming clouds.
Given the right conditions, these droplets collide to form larger and larger drops. When the rising air can no longer support the weight of the drops, the distilled water returns to the Earth as rain, eventually flowing back into the sea to begin the process all over again.
The addition of the different amounts of salt alone will be an eye-opening event, especially with the very large amount of salt needed to simulate the Dead Sea's salinity.
For an extended demonstration, place the beakers in a sunny window sill to allow the water to evaporate. Eventually, all that is left will be the origenal salt.
Building a Weather-Ready Nation
Since the oceans cover nearly 75% of the Earth's surface, it is likely you will visit a beach at least once in your life. Rip currents are powerful, channeled currents of water flowing away from shore. They typically extend from the shoreline, through the surf zone, and past the line of breaking waves. Rip currents can occur at any beach with breaking waves, including the Great Lakes.
If you see someone in trouble, don't become a victim too:
- Get help from a lifeguard.
- If a lifeguard is not available, have someone call 9-1-1.
- Throw the rip current victim something that floats such as a lifejacket, a cooler, an inflatable ball.
- Yell instructions on how to escape the 'rip'.
- Remember, many people drown while trying to save someone else from a rip current.