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Salt Solution Experiments with Mrs. Wizard

July 18, 2009
Comparing salinity

Comparing salinity

We are doing a unit study on salt, because salt rocks. It brings together history, economics, biology, chemistry, art, cooking … you name it, salt probably  has something to do with it.

We are reading aloud The Story of Salt, doing projects and chemistry experiments with salt, and making a salt lapbook. We’re tying this into our study of Ancient Egypt by mummifying grocery store chickens in lots of salt. We made ice cream in Ziploc bags and learned that salt lowers the melting point of ice (which happens to tie in neatly with our study of changes of state). On the spur of the moment, we mixed up two heavily saturated salt solutions and made salt crystals. And this past Thursday, our friend and once-a-week  homeschooling partner, Mrs. Wizard, led our little group through a couple of great experiments with salt solution.

Like water, salt solution bends light … but it bends it more than plain water. If you want to spring for a refractometer, you can use it to measure salinity. We didn’t particularly feel that our third-grade chemistry lab needed a refractometer, and a pencil in salt water doesn’t look materially different from a pencil in plain water. However, Mrs. Wizard nevertheless showed the kids how to compare the salinity of four cups of liquid based on how much the liquid bent light. In clear plastic cups, she made three salt solutions with different concentrations of salt, and she put plain water in a fourth cup. Then she held a strip of white foam board (anything white will do) behind the cups and had the kids shine a laser pointer through the cups. When you shine it through the plain water, you get a rather neat red dot on the white board. However, when you shine it through salt solution, you get a fuzzy dot. Moreover, the more salt is in the solution, the fuzzier the dot gets. The kids could easily arrange the cups in order from no salt to most salt based on their observations.

Completing a circuit through salt water

Completing a circuit through salt water

The science did not stop there. Salt solution conducts electricity. Mrs. Wizard rigged up some batteries and wires and a lightbulb and stuck the ends of two wires in the plain water to see if that completed the circuit and lit up the light bulb … nope. But as you can see, sticking the wires in the salt water did complete the circuit to light the bulb. Moreover, the more salt in the solution, the brighter the bulb glowed. (This was a little hard to see; however, she had The Bean pour one of the salt solutions into the plain water while the wires were in it until we could see the lightbulb start to dimly glow in the weak solution.)

Completing a circuit through a pickle

Completing a circuit through a pickle

Now, salt also preserves food, including cucumbers in the form of pickles. You know what’s fun? Completing a circuit through a pickle. My flash sort of ruined the effect for the photo, but the lightbulb definitely glowed when a pickle was inserted between the wires, proving that electricity can flow through pickles. I’m not sure how often that particular bit of trivia might come in handy in our students’ lives, but I doubt they will forget it any time soon!

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