NSC 101 Laboratory for 4/14/97

This lab will provide an introduction to physical states and to chemical reactions. The first experiment will involve mixing water and cornstarch. You can do this at home if you just can't wait! The second experiment will involve heating the metal magnesium until reacts with the air.

Equipment: Cornstarch, 200 ml beakers and water, crucibles with lids, gas burners and ring stands, magnesium ribbon.

Procedure:

1. First, we will make what Dr. Zeuss calls oobleck. Put about a quarter cup of water into a beaker and stir in a bit (~ 1 tsp) of cornstarch. Let it set a few moments and observe. What happens? Now add more cornstarch, in very small amounts, and note what happens as the mixture stiffens. Over the sink, pour the thick mixture into your hand squeeze. Discuss what is peculiar about this mixture and its behavior under stress.

2. Each group will get about 10 cm of magnesium ribbon. Clean the oxide off with steel wool or scrape with a knife. Heat a crucible for a few minutes to drive off any moisture and weigh it when cool. Place the ribbon in the crucible and weigh it again. Now heat the ribbon in the crucible with the lid on, but with just a crack to allow observation. When the ribbon is completely white, turn off the burner and let the crucible cool. Weigh it again and compare the weight of the contents before and after.

   Using the periodic chart, calculate the formula for magnesium oxide and predict the additional weight of oxygen in the crucible. Is the value you calculated the same as the actual increase? What other elements are in the air? What other compound might be in the crucible?