Todays lab, Recrystalization, is from the CK01A Instruction manual that goes along with the Honors Chemistry kit.   You can download the manual for free from the Home Scientist website by clicking on the link above.  In this lab the students mix some sodium bicarbonate (baking soda)  and sodium chloride (salt), then slowly add it to cold water until the solution is saturated. They then heat the water until it boils and add more mixture until its saturated again. IMG_4062 We then let the solution cool and watch crystals form on the surface and sides of the beaker.  IMG_4067Once the beaker has cooled we placed it in the freezer to further cool the supersaturated solution and let even more crystals form.  Some of the liquid  is then poured off into a test tube, while the crystals are rinsed with cold water and then laid out to dry on paper towels.  IMG_4068The students then put a few drops of HCl into the test tube to test for the presence of baking soda,  the HCl reacts with sodium bicarbonate and forms salt, water and carbon dioxide, the last of which is a gas and forms bubbles.  Everybody got lots of bubbles because even though some of the sodium bicarbonate crystallized out of solution, the solution still contains a lot of it.

The students measured the mass of the salt and baking soda mixture before they started adding it to the water, and measured it again each time the solution was saturated so they could calculate the mass of material dissolved in their solution.   We have two hours for class and ran out of time, it would have been nice to leave the solutions in the freezer longer but class was over so we had to rush a bit at the end.

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I recommended the students watch Crash Course Chemistry #21 lab techniques

and a video by Tyler DeWitt on scientific notation.

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