Reactivity of Halide Ions

 

Objectives

 

Introduction

The following salts used in this experiment are found in your body.  Although sodium fluoride is poisonous, trace amounts seen to be beneficial to humans in the prevention of tooth decay.  Sodium chloride is added to most of our food to increase flavor while masking sourness and bitterness. Sodium chloride is essential for many life processes, but excessive intake appears to b e linked to high blood pressure.  Sodium bromide is distributed throughout body tissues, and in the past it has been used as a sedative.  Sodium iodide is necessary for the proper operation of the thyroid gland, which controls cell growth.  The concentration of sodium iodide is almost 20 times greater in the thyroid than in blood.  The need for this halide salt is the reason that about 10 ppm of NaI is added to packages of table salt labeled “iodized”.

The principal oxidation state of the halogens is -1.  However, all halogens except fluoride may exist in other oxidation states.  The specific tests you will develop in this experiment involve the production of recognizable precipitates and complex ions.  You will use your observations to determine the halide ion present in an unknown solution.

 

Text Box: SAFETY

For this experiment, wear safety goggles, gloves, and a lab apron to protect your eyes, hands and clothing.  If you get a chemical in your eyes, immediately flush the chemical out at the eyewash station while calling to your teacher.  Know the location of emergency lab shower and eyewash station and the procedure for using them.  NO HORSE PLAY in the laboratory.

Text Box:

Do not touch any chemicals.  If you get a chemical on your skin or clothing, wash the chemical off at the sink while calling to your teacher.  Make sure you carefully read the labels and follow the label, as your teacher what precautions you should follow.  Do not taste any chemical or items used in the laboratory.  Never return leftovers to their original containers; take only small amounts to avoid wasting supplies.  ]

Text Box:

Call your teacher in the event of a spill.  Spills should be cleaned up promptly, according to your teacher’s directions.

 

Never put broken glass into a regular waste container. Broke0n glass should be disposed of properly in the broken-glass waste container.

 

 

pipets
 
Go to fullsize imageMaterials and Chemicals needed:

 

0.1  M AgNO3

0.1 M NaCl

0.1 M NaF

0.2 M NaBr

24- Well MICROPLATE

6 rows of four wells
 
0.2  M NaI

0.2 M Na2S2O3

0.5 M Ca(NO3)2

3% starch solution

4 M NH3

5% NaOCl (commercial bleach)

24-well microplate

Thin-stemmed pipets, 12

 

Procedure:

 

Part 1 - Getting Ready:

 

  1. Put 5 drops of 0.1 M NaF into each of the four wells in row A. 
  2. Put 5 drops of 0.1 M NaCl in each of the wells in row B.
  3. Put 5 drops of 0.2 M NaBr into each of the wells in row C.
  4. Put 5 drops of 0.2 M NaI into each of the wells in Row D. 
  5. Reserve rows E and F for unknown solutions.

 

PART 2 - Performing the Reactions of the known halide solutions

 

1.      Add 5 drops of 0.5 M Ca(NO3)2  solution to each of the four halide solutions in Column 1.  Record your observations in a data table.

 

2.      Add 2 drops of 0.1 M AgNO3 solution to each of the halides in column 2 and 3.  Record your data table colors of the precipitates formed.

 

3.      Add 5 drops of 4 M NH3(aq)   solution to the precipitates in column 2.  Record your observations.

 

4.      Add 5 drops of 0.2 M Na2S2O3 solution to the precipitates in column 3.  Record your observations.

 

5.      To the halides in column 4, add 5 drops of starch solution and 1 drop of 5% bleach solution.  Record your observations.  Save the results of testing the four halide solutions for comparison with tests of the unknown solutions.

 

PART 3 - Unknown Solution for testing

 

  1. Obtain an unknown solution containing a mixture of two halide ions. 
  2. Place 5 drops of the unknown mixture in each of the four wells in row F.
  3. Add the reagents to each well as you did in Part 2.
  4. Compare the results with those of the known halides in rows A-D.
  5. Record your findings in the data table., and identify the unknowns in your sample.

 

PART 4 - Clean up and Disposal

 

 

  1. Rinse the microplace in to the dishpan on the back sink counter.
  2. Clean all apparatus and your lab station.
  3. Return all equipment to its proper place.
  4. Lock you drawer.
  5. Dispose of chemicals and solutions in the containers designated by your teacher. 
  6. Do not pour any chemicals down the drain or in the trash unless your teacher directs you to do so.
  7. Wash your hands thoroughly before you leave the lab and after all work is finished.

 

 

Data Table

 

Halide Salts

 

Ca(NO3)2

AgNO3

AgNO3 + Na2S2O3

NaOCl + starch

NaF

 

 

 

 

 

 

 

NaCl

 

 

 

 

 

 

 

NaBr

 

 

 

 

 

 

 

NaI

 

 

 

 

 

 

 

Single unknown

 

 

 

 

 

 

 

Double unknown

 

 

 

 

 

 

 

 

Questions, General Conclusions and Summary Statement (see your copy for this)