Tested Overhead Projection Series Compiled by HUBERT N. ALYEA Princeton University

E. Metals and Alloys 2. ALLOYS (Continued)

Dem. 426-Low-melting Alloys

Experiment developed by Crosby U. Rogers and Charles Owens.

To show: Alloys melting below the hoiling point of water.

Materials: H-3, 0-100°C thermometer, low-melting alloy such as Woods' Metal or "trick" spoons available a t trick supply houses.

Preparation of rod: Melt about 10 ml of metal by plac- ing it in a test tuhe immersed in boiling water. Insert a 7-mm tubing 8 in. long to which is attached 2 f t of rubber tubing and suck i n (CARE: have glass tuhe to bottom on molten alloy) 6 in. of molten metal. Cool to solidify. When cool, break the tubing to give a 5 X 150-mm rod of alloy.

Procedure: Suspend the rod in a culture tube full of water. (a) Place in H-3 over a burner; project; heat. (b) Allow to cool; place a thermometer in the water and record the temperature a t which the alloy solidifies.

Observations: The rod melts and drips into the hot water long before the hoiling point of water is reached.

12. GROUP I. THE ALKALI METALS. THE COPPER GROUP

A. General Contrasts 1. PHYSICAL PROPERTIES

Dem. 427-Density of Copper versus Sodium

Experiment developed by Carl J . Mancuso.

To show: The relative densities of copper and sodium; and the rapid reaction of sodium with oxygeil and moisture in the air.

Materials: Five pennies, copper coins, lump of sodium; balance SD-20-K, knife. J. Chem. Educ., 40, A886 (1963).

Procedure: (a) Freshly cut a piece of sodium about the same diameter as a penny but 2 em high. Counter- balance it with pennies (about 3), with the balance tipped slightly in favor of the coins. (b) Project for 15 min.

Observations: (a) The chunk of Na is trine times larger than the Cu (densities 0.97 vs. 8.94). The difference in volume is striking. (b) In about 5 min the balance tips in favor of the Na as it picks up oxygen (forming Kaz02 and NazO) and moisture (forming NaOH) from the air.

Dem. 428-Melting Point of Cu versus No

Experiment developed by Carl J . Maneuso.

To show: The low melting-point of sodium contrasted with that for Cu. (Na = 97.5OC; Cu = 1083'C).

Materials: Sodium lumps, toluene, H-3, Cu wire.

Procedure: (a) Drop three 0..5 mma chunks of Na into a culture tube half full of toluene. Dry outside of tuhe (CARE: toluene is a fire hazard; do not use CCll which explodes with Na). Insert in H-3 and project. Heat gently. (h) Hold Cu wire in flame.

Observations: The pieces of Na melt into a smooth ball at the bottom of the toluene. The Cu wire melts with difficulty.

Dem. 429-Conductivity of Sodium

Experiment developed by Carl J. Mancuso.

To show: Conductivity of sodium

Materials: ?&-amps with wire terminals fastened to 2411. lengths of Ko. 18 Cu wire; a 2-cm3 hlock of Na (if available, Na wire).

Procedure: (a) Project Me-amp, with 1.5 volt dc source attached, turn on switch, push the stiff Cu wires into the block of sodium. (b) Exhibit Na wire; also show it conducts.

Observations: At 1.6 volts approximately 1 milliamp flows.

2. CHEMICAL REACTIONS

Dem. 430--Reactivity with Water: IA vs 18

To show: The relative rates of reaction with wat,er of members of the alkali metal and copper groups (Groups I-A and I-B).

2Na + 2H.O - 2NaOH + H. 1 ; Cn + H20 - n:] react,inn

Materials: Copper coin, silver coin, 2 mm lumps of Na and I<, 4 X 4 X 1 in. plastic, wood, or carboard, and marked with wax pencil "Cu, Ag, Ka, and Ii" respec- tively. Phenolphthalein indicator, solid detergent, ,5 X F, X in. plastic cover-plate, forceps, horizontal pro- jector.

Volume 44, Number 10, October 1967 / A91 9