Halogen Chemistry

Introduction

This experiment provides an opportunity to investigate the reactivity of some of the halogens ("salt-formers") in water solutions. The lab will be accomplished using microscale techniques and equipment.

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1. Obtain one clean, dry, plastic, 12-well, cell culture plate and an audio cassette container marked Halogen Chemistry.
2. Add 6 drops of oil from the pipet to wells # 1-2-3, 5-6-7, and 9-10-11 leaving wells 4, 8, and 12 empty.
3. Read the rest of the procedures (but do NOT "do" them at this time!), then design a data table in which you will organize data. This table should allow you to recall what was put in each well as well as whether or not observations were made which led you to believe that a chemical reaction had occurred.
4. Add 6 drops of chlorine water to wells # 1-2-3; then 6 drops of bromine water to wells # 5-6-7; and 6 drops of iodine water to wells # 9-10-11. Record any observations in your data table.
5. Add 6 drops of distilled water to each of wells # 3, 7, and 11. Add 6 drops of KBr solution to wells # 1 and 10; then 6 drops of KI solution to # 2 and 6. Also add 6 drops of KCl solution to wells # 5 and 9. Observe and record observations. Dispose of the contents of your 12-well plate in the lab sink. Rinse with soapy water and a cotton swab. Turn in plate and chemicals. Be sure to wash your hands with soap and water!
6. Based on your observations, complete and balance equations below for those reactants which you believe reacted. Write N/R to the right of the arrow if you observed no reaction.

   KBr + Cl₂ -->

   KI + Cl₂ -->

   KCl + Br₂ -->

   KI + Br₂ -->

   KCl + I₂ -->

   KBr + I₂ -->

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1. Which of these three halogens (Cl₂, Br₂, I₂) is the most reactive?
2. Which is the least reactive?
3. Why do you suppose fluorine was not included?
4. Where do you predict fluorine would have ranked and why?
5. Are there any other halogens left out of the lab? Why?

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Wear eye protection and an apron. Halogens are toxic. Do not inhale vapors of halogens. Do not ingest halogens. Use liquid bleach with caution. It is corrosive, causes blindness, and damages clothing. Wash spills immediately.

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1. Chlorine is the most reactive.
2. Iodine is the least reactive.
3. Fluorine is so reactive that it cannot be included since it reacts with those materials that would be used to manufacture the container.
4. Because fluorine is so reactive, it would have ranked at the top of the reactivity list.
5. Astatine and fluorine are left out. Fluorine is too reactive. Astatine is a radioactive and mostly man made element.
   

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The first, second, and fourth reactions will display color changes in procedure six, as expected (single replacement reaction). You may wish to leave wells # 4-8-12 empty and suggest that the student provide a second control combination.

2 KBr + Cl₂ --> 2 KCl + Br₂

2 KI + Cl₂ --> 2 KCl + I₂

2 KI + Br₂ --> 2 KBr + I₂

Fluorine is too reactive to use is routine experiments.

Astatine is a radioactive element all of whose isotopes have relatively short half lives (the longest-lived isotope has a half-life of 8.3 hours); it was not included for those reasons. It behaves like iodine.

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• aterials
• chlorine water (acidify 100 mL Clorox^® with 6 drops concentrated HCl)
• bromine water (dissolve 4 grams KBr in 50 mL Clorox¨)
• iodine solution (dissolve 1 gram KI in distilled water, adding 0.5 g I₂ , and diluting to 50 mL
• mineral oil
• 1 M KCl (dissolve 4 grams KCl in 50 mL water)
• 1 M KBr (dissolve 6 grams KBr in 50 mL water)
• 1 M KI (dissolve 8 grams KI in 50 mL water)
• 12-well plastic cell culture plates
• 20 Beral pipets
• 300 toothpicks

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The microscale adaptation of this lesson was developed by:

John McNeilly
Nebraska City HS
Steinhart Park Road
Nebraska City, NE 68410

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