R. J. FRIESEN, editor 1 , , University of Waterloo

Waterloo. Ontario, Conoda

A Lab to Motivate Weak Students

GlenLoueridge Silver Heights Collegiate 350 Lodge Avenue, St . James, Manitoba RM OM8

Teachers need help motivating weak science students, motivating them t o complete the course, a n d motivating them t o t ry a science course. I'd like to help by sharing my ideas.

One lah which I have found to he very good is described below. I can use i t with almost any type of class. If I have covered half reactions a n d the oxidation potential table, I can insist on balanced half reactions or equivalent weights. But better still, I can use it with any class to in- troduce electrolysis. Depending on the ability of the class, I may ask for observations alone.

Object

T o study a n electrolysis reaction.

Introduction

T h e electrolysis will he done in a jelly. T h e n if the apparatus is moved, the results of the electrolysis will not mix.

Method

Depending an your class:

reactions.

1) Put l.W g of compound into a 250-ml beaker. Add 20.0 ml of water and make a solution.

A) Give them the name potassium iodide, then insist on half

B) Give them no name, and let them try to determine what was present.

C) For some classes you may want to say it is a compound which liberates hydrogen ions and iodide ions.

2) Heat the solution until it boils, then add 0.2 g of agar. Con- tinue to heat and stir until the solution boils again. 3) Obtain two pieces of copper about 10 em long, bend into a semi-circle and have one end extending up. Place into a Petri dish, as shown, then pour in the hot mixture. Do not let the two pieces of copper touch. 4) Saturate a sponge with cold water. Put the Petri dish on the sponge and let cool until a jelly forms. This will take 5-10min. 5) once the mixture hasset completely into a jelly, attach the copper wires to a 6-V battery and subject the mixture to electml- ysis. Let electrolysis reactions continue for about 5 min. 6) Then disconnect the terminals and pull the capper wires out of the jelly. Have a good look at everything. Put your fingers into the jelly and try to determine what happened. Smell the jelly and your fingers. 7) Put the copper and jelly into the garbage. Clean up and put away your apparatus.

T h e s tudents can see the brown iodine formina, thev can smell it and some recognize i t . Some students kill nd- t i re bubhles forming on the other wire, and , depending on their abilits. will recomtze them as hubblesof hvdn,eetl. ~ ~

As a teacher, you will have to decide o n what t o a s k for in the lab reports. This will depend o n the ability of the class.

Brass

P. D. McCormick Thorold Secondary School Ormond Street North Thorold, Ontario

This experiment constitutes a rather spectacular illus- tration of a diffusion process in solid copper. Mr. A. T. Nathan, Central Technical School, Toronto, Ontario, first presented i t to a group of teachers who were just hegin- ning participation in a Solid S ta te Structure and Reac- tions Program sponsored by t h e American Society for Metals.

Experiment

A small spoonful of zinc dust is placed in an evaporating dish, and covered with 3 M to 10 M sodium hydroxide solution. This is heated to a steaming temperature, whereupon a clean copper token is immersed in the hot zinc-plating bath. When the plating bath is active, numerous bubbles of hydrogen will escape from the mixture and heating may he temporarily discontinued. A silvery coating of zinc will develop on the copper. When this plating pm- cessiscompleted, the token should be washed and dried.

The zinc may be caused to diffuse into the copper by holding the token, with tongs, in the outer cone of a Bunsen flame. The token will suddenly turn yellow as a brassy coating is formed. It is heated for two or three more seconds and immediately quenched in water to prevent oxidation. The copper will appear to have been transformed into a brass token.

Notes 1) A practice to be discouraged is the use of the copper tokens

which are available, for the price of one cent, from the Canadian 0rU.S. Mint.

2) c u t the copper token in hall and examine it for depth of penetration of the brassy coating. 3) If the brassy token is left undisturbed for one or two days,

the upper surface will revert to its original copper color while the lower surface remains brassy. Why?

4) The most frequent defect obtained by the student is oaida- tion of the brass by overheating.

5 ) Try reversing the brass-forming process by heating a piece of brass shim stock (0.005-in. or greater in thickness) in the flame of a Meker burner while the other end is in a beaker of cold water. You should be able to volstilize the zinc from the brass over the hottest part of the flame, and observe a return to a copper color. A bonus to this part of the experiment is obtained if you etch tbe brass with 30% HNOa-70% cone. H202 whereupon large crystals can he observed microscopically at the heated end of the brass strip. These become progressively smaller toward the colder end of the brass sample. 61 Brass is fun stuff to work with, and any old brass door knob

should yield its crystalline secrets when etched either hv cantinu- ous usebr by the etchant described above.

Editbr's Note: Chem 13 News is an informal publication of the Department of Chemistry of the University of Wa- terloo, addressed primarily to Ontario high school chemistry teachers. This column is the first of a bimonthly series of selections from Chem 13 News by R. J. Friesen, one of the editors. The other editors are J. L. Candida of Kitchener Waterloo Collegiate Institute and Vocational School and W. A. E. McBryde of the University of Waterloo.

102 / Journal of Chemical Education