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

19. GROUP VI. THE SULFUR FAMILY

Dem. 563-PbS + H D ,

Toshow: Therestoration of paintings blacked by PbS. Materials: lead acetate-aq, 3% hydrogen peroxide, cell C-2, stirrer, NazS-aq, H2S04-dil.

Procedure: To 50 ml water add 8 drops each of (CHa- COOj2Pb and NasS-aq; a slight black precipitate should form; if i t does not, add more of the two re- agents. Two-thirds fill each cell of C-2 with this (a) Stir. (b) Into one add one drop HaSOrdil. plus 5 ml of 3% HsOi Stir.

Observatzons: (a) Black PbS forms, and settles to the bottom of one cell. (6) In the other cell, the PbS dissolves to form white PbSOi (exhibit macro) which projects paler than (a).

Reactions: (a) (CHaCOOjiPb + NazS -* 2 CHZ- COONa + PbS 4 (black). (6) PbS + 4 Hz02 +

4 H 2 0 + PbS04 (white).

D. Sulfur Dioxide Dem. 564-Preparation of Sulfur Dioxide

To show: Preparation of sulfur dioxide. (See Den%. 559).

Materzals: NaHSO,, HCl-dil. cell G-1, Iatn04-dil. , plastic strip about 6 X 2-in.

Procedure: Project G-1 with 5 g solid NaHSOa in the generator chamber, HCI-dil in the dropper, and the receiving chamber empty. Coat the plastic strip with a pink layer of KMn04-aq, and lower it into the re- ceiving chamber Drop the acid upon the solid.

Obsewalzons: As SO2 is evolved, it decolorizes the per- manganate solution If KsCr&aq is used, green Cr+3 forms.

Dem. 565-SO, from SO,= or HSOc

To show: Preparation of sulfur dioxide.

Materials: NaHS03, Na2SOa, HCl-dil., NaCl, cell C-3, three thin plastic strips about 6 X 2-in , KMnO.- an.

Procedure: Place Na2S03, NaCl, and XaHSOg respec- tively in the three cells of C-3; do not tell the class which each contains, let them guess at the conclusion of the experiment Make each plastic strip pink with KMn04-aq. Project the cell and contents, add some drops of HCl-dil. to each chamber, lower into them the plastic strips. Observations: The bisulfite and sulfite chambers, but not the NaCI, generate SO2 which decolorizes the per- manganate. Reaction equations are given in Dem. 564.

Dem. 566-Liquefaction of Sulfur Dioxide

Experzment developed by Isjrzn Noerdin and Crosby U . Rogers.

To show: The preparation and liquefaction of SOa

Materials: Special device SD-566. See Figure Ace- tone, dry ice, HCl-dil , NaHSOa.

SD-566. Liquefaction Apparatus.

Construction of SD-566 A 4-02 wide mouth clear glass square bottle. Inside, stick with wax 2 flat-bottomed vials about 1 in. high and about V S and 314-in. in diameter. Insert a one-hole stopper earning a 13 X 100 ml test tube projecting inside the bottle, and file a slit along the side of the stopper to permit escape of excess SO%.

Procedure: Project SD-566 with 1 ml water in vial B, with 5 g NaHSOa + 5 ml HCl-dil in vial A, and with dry ice-acetone mush in tube C.

Volume 45, Number 12, December, 1968 / A977