GRAPE JUICE AS AN INDICATOR Submztted by: Joseph F. Castka, C. W. Post College of Long IslandUniversity, Brookville, New York Checked by: George Ferris, Michigan State University, East Lansing
PREPARATION
Dilute 20 ml of Welch's Grape Juice (no sugar added) to 200 ml. Provide test tubes, droppers, red and blue litmus paper, a dilute acid solution (vinegar will serve), a dilute base solution (ammonia will serve), sodium bisulfite (NaHSOg),and 3% hydrogen peroxide solution. DEMONSTRATION
Set up three test tubes containing 10-ml samples of the diluted grape juice. To one add a few drops of the acid solution, leave the second one for comparison, and to the third add a few drops of the base solution Observe and record the color. Compare with the action of these solutions on litmus papei. The neutralization process may he followed by adding a base to the first
test tube until the color changes and by adding an acid to the third test tube until the color changes. Again compare the action of these solutions on litmus paper. Arrange three additional test tubes each containing 10-ml samples of the diluted grape juice. Add a few drops of hydrogen peroxide to the first test tube and a small amount of solid sodium bisulfite to the third test tube, stir, and compare the colors of the three solutions. Add hydrogen peroxide to the third test tube until the original color reappears. REMARKS
The above may be used as an "open-ended" experiment by suggesting that students try other acid-base and other oxidizing reducing reagent combinations.
GASEOUS DIFFUSION Submitted by: H. Bradford Thompson, Gustavus Adolphus College, St. Peter, Minnesota Checked by: Dale Drcishach, Hiram College, Hiram, Ohio
PREPARATION manometer hquid Fold a 12 X 12-in cloth square and secure in the bottom of an 800-ml beaker using a snap made from a test-tube clamp (see fig ). Provide another 800-ml beaker and carbon tetrachloride.
DEMONSTRATION Invert a beaker over the cup and introduce burner gas into the beaker: Diffusion of the light When pressures equalize, remove beaker: Net outward diffusion is shown by decreased pressure. Wet the folded cloth with carbon tetrachloride and place this beaker over the cup: Pressure decreases. When pressures equalize, remove heaker: Pressure increases.
gaa inward is shown by increased pressure within the cup.
NOTES I . This exnwirnent., a modification of t,hoos of A .h a ("Tested Demonstrations in General , l i " Tin-. Ji.rh.\.\i., M,ircti, 1955 mu1 .5utton ,~l),~rnonsirati~,n l:xprriii.i-ms in. l'l.,si ' Mc',ir:i~~-lIill. 1938 p. 166 . I n 3 thr ,iilv:iiil~goofJf-miin;.rr:irin)3; r h e s . t ~ . fpoint i i f u r lilnes, ,ttA of ~ 5 1 r ~x ~ ~ ~ . l ~ l ~ - v: .~L vI ~:
