Mixtures - a mix of two substances that are mixed together but not combined chemically. The ingredients can be removed from the mixture afterwards.
Bonding - when the atom in separate things mixed together form chemical compounds, where the electrons are shared, and they become something different than the initial ingredients added.
We did an exercise in class where we did two different kinds of experiments. To examine mixing, we combined cornstarch and water. While the cornstarch and water mixed together and became thicker and harder, it was still just a mixture, and nothing chemically happened. To examine bonding, we mixed Elmer's glue with hot water, shook it for a while, and then mixed in a powdered borax soap. It became this flubbery glue - obviously a chemical change happened.
We realize that once the water has evaporated from the cornstarch solution, we can see the cornstarch in the glass. This is part of the mixture, you can separate the ingredients. We will never be able to pull the Elmer's glue back out of the goop that we made, therefore, a bond happened.
Great posting. Ok, we also did a crystal garden, right? "Table salt (NaCl) can be dissolved in water. The amount of salt in a particular quantity of water depends on its temperature - more being soluble in warmer water.
ReplyDeletePeople who live near the ocean often transfer sea water to open pools where evaporation can take place. This is still done in the Hawaiian Islands where there is an extended dry season.
As water evaporates, some of the salt cannot be retained and crystals of salt form along the edges of the pools and finally when all the water is gone there will be crystals on the bottom of the dried pool. These need only purification to be used as table salt." Stewert's web site. http://www.mrsstewart.com/pages/explanation.htm