Tested Overhead Projection Series Compiled by
HUBERT N. ALYEA Princeton University
20. GROUP VII. THE HALOGENS
A. General Reactions 2.
RELATIVE REACTIVITY OF THE HALOGENS (Continued)
Dem. 593-Concentrated
HSO,
+ NaX
Experiment developed by Raymond P. Garnaan. To show:
Interaction of conc. HzSOn on the halides.
Materials: NaC1, NaBr, NaI; conc. H2S06; H-3; Filmstrips SD-4 with the gelatin soaked in (a) litmus t o deep red and (b) P b ( o A ~ ) ~ - a q . Procedure: (a) Project 1 g of iYaC1, of NaBr, and of NaI, respectively, in 3 culture tuhes in H-3. Add 5 drops conc. HzSOI to each. (b) Lower litmus-colored filmstrips into tubes 1 and 2, and P b ( 0 A ~ ) ~ c o a t e d filmstrip into tube 5. Observations: HC1 gas forms in tube 1, and turns litmus pink. Both brownish Br2 and SO? form in tube 8; the latter turns the litmus pink and then bleaches it. Both violet I2and H B form in tube 5; the latter forms black PbS with the Pb(OAc)%filmstrip. Equations: H80n +++2H,SO4 5KSO1
NaCl 2NaBr 8NaI
---
+++
NrtHSO, HCI NdOl 2H20 Bh SO1 4NanS0, 4HzO 412 H,S
+ + + +
Dem. 594-Bmmide
versus Iodide
l b show: Analytical tests distinguishing between chloride, bromide, and iodide.
Materials: Clz-aq, CC14 or CS2, XI, KBr, NaCl, C-3, and 6 test tubes. Procedure: Project C-3 containing 6 test tuhes each '/2 full of water and immersed in water. Into each drop 1 ml of Clraq. Now drop a pinch of solid into each (do not tell the class which), hut use NaC1, NaBr, and K1. (a) Project; stir. (b) Now add 5 ml CS2to each and stir again. Observations: The class can identify which are hromides or iodides in the aqueous tests, but cannot distinguish Brz from 1%.Upon adding CSz, this layer turns violet with 1%. in the Presence of Br- and I-
Experiment developed by August J . Colo and W. H. Slabaugh. To show: Analytical test in special device using minute amounts of reagents.
-
Reactions: 2HC1 2H20 2HC1 Ag,Cr04.
+
3. Analytical
Dem. 595-Chlorides
SD-595.
-
Gas-Testing Apparotvr
+ CrOa Cr02C1+ HsO; Cr02C1 + H2Cr04; latter forms PhCr04 or
Materials: Special Device SD-595. See Figure; NaCl, KI, KBr, conc. HzSOI, Ii2Cr2O7,Pb(NO&aq, AgN03aq. Procedure: Project SD-595 with conc. HzS04 in the dropper. I n the culture tube place 0.5 g NaCl 0.5 g NaBr 0.5 g Ii%Cr2Oi. Tube must be dry. (a) Put 3 ml water in the bottle. Drop conc. HzSOa into the mixture in the culture tube. (b) Repeat, with 3 ml Ph(NO&aq in the bottle. (c) Repeat, with 3 ml AgNOa-aqin the bottle.
+
+
Observations: Yellow chromyl chloride gas (Cr0,Cl) is evolved and gives (a) with water, a yellow solution, (b) with Pb++, a yellow precipitate of PbCr04, and (c) with Ag+ a red precipitate of Ag2CrOa. Exhibit macro. Note. The precipitates form slowly (in 5 min). Avoid moisture in the culture tube.
Reference: HEATH,E. H., J. CHEM. EDUC.,25, 73 (1948). MCALPINE, R. K., and SOULE,B. A,, Qualit* tive Analysis, D. Van Nostrand Co., Princeton, N. J., 1933, page 530. Volume 46, Number 3, March 1969
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