Oct 13, 2011

How to Separate Salt and Sand

     I’m sure you’re a little curious about the title because it sounds a little odd, bear with me for a bit it will all make sense here soon. I have really wanted to do more science with the kids but we still don’t seem to have enough hours in the day, my goal is now one experiment each week or one “unit” each month. Last week I presented the kids (meaning mainly Boo) with a challenge to see if they could think about a problem and try to solve it rather than reciting facts back to me. We do memorize but I think kids need to learn to solve and think also, so last week that was the goal.

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     I’m sure you are asking yourself why I have a picture of mud in a measuring cup, well that’s part of our experiment, we basically made mud, not just any mud though, it was salty mud. Here was what I presented to Boo, a bag of sand and salt mixed together. The next step was for him to figure out how to separate the two, leaving sand in one pile and salt in another.

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    I mixed 1/3 cup salt and some sand in the bag, and handed it to Boo to separate, and stood back to see what he did. First he found our strainer and tried that way, no luck, so I suggested trying to add water. He then added water and thought the salt disappeared, until they stuck there finger in and tasted it.

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     Then he wanted to run the muck through a cloth, his point was that the cloth had smaller holes, so he used cheese cloth to “strain” the salt out.

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     The kids again tasted the water, still salty. They had how ever managed to separate the sand and the salt with very little help from me. Next they had to figure out how to get the salt out of the water. Boo’s solution to the problem was if the cloth caught the sand then we just needed something with smaller holes to catch the salt. Now for his “filter”.

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     He used a pair of Sis’s holy tights, a scrap of terry cloth, and lots of cotton balls. I pretty much let the kids figure out what they wanted to use as the filter (within reason). The filter got the remaining dirt out of the water and it almost looked just like it did to start with. The kids at this point thought they had solved the problem and got really excited, until I asked where the salt was. Boo took the filter apart and could only find dirt. Then he tasted the water, salty. They where stumped for a little while until I suggested they put the salty water in a pan on the stove and see what happens.

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     Once we got the water boiling I took the opportunity to talk about evaporation and condensation and put a lid on the pan. Once the condensation started to build on the lid I took the lid off and let the water drip into a clean container so the kids could taste the clean water.

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     I think at that point it created more questions because the water in the pan was still salty but the water that was evaporating wasn’t salty. I ended up turning the burner on high to speed things up because the kids where starting to get distracted.

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     Once almost all the water was evaporated we just let it sit out to finish drying. When it was fully dry (a couple of days latter) we decided to measure it and got almost 1/3 cup back, I was impressed, I thought we would loose more than we did.

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     The kids now know how to get clean water, what evaporation and condensation are, and how to separate salt and sand. It was defiantly a successful experiment.

Thanks,

Len

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