anions tests

Topics: Ion, Ammonia, Sodium chloride Pages: 8 (2536 words) Published: April 26, 2014
EXPERIMENT TWENTY

Qualitative Analysis
of Anions

Analysis of Solutions Containing the Ions
Cl-, Br-, l-, SO42-, CO32-, and NO3-

This experiment continues the qualitative analysis begun in Experiment 19. Here we will be analyzing solutions to determine the presence of anions. The same techniques that were used for the cation analysis must be used for the anions. If you have not carried out Experiment 19, read the introductory section before starting this experiment. The major difference between cation and anion analysis is that in anion analysis, a series of separations of the ions from one another is usually not the most efficient way to determine their presence. Instead, only some separations will be made, and the initial test solution will be used to test many of the ions. Refer to the flow chart at the end of the experimental directions as you proceed.

First you will prepare and analyze a “known” solution which contains all six of the anions. Then you will analyze an “unknown” solution using the same techniques, to determine the presence or absence of each anion.

As in Experiment 19, a description of the physical properties and the chemistry of the substances appears in boxed frames.

Chemicals

Solutions of Anions:

Sodium chloride, NaCl, 0.2 MSodium bromide, NaBr, 0.2 M

Potassium iodide, KI, 0.2 MSodium sulfate, Na2SO4, 0.2 M

Sodium carbonate, Na2CO3, 0.2 M Sodium nitrate, NaNO3, 0.2 M

Test Reagents:

Silver nitrate, AgNO3, 0.1 MAmmonia, NH3, 6 M

Nitric acid, HNO3, 6 MPotassium permanganate, KMnO4, 0.1 M

Mineral oilSodium hydroxide, NaOH, 6 M

Barium hydroxide, Ba(OH)2, saturatedBarium chloride, BaCl2, 0.1 M

Acetic acid, HC2H3O2, 6 MAluminum(s), granules

Iron(III) nitrate, Fe(NO3)3 0.1 M in nitric acid,
HNO3, 0.6 M

To neutralize spills:

Baking soda, NaHCO3(s)Vinegar, HC2H3O2

Equipment

Test tubes, 6, 13- x 100-mmTest tube rack

Wire test tube holderBeaker, 250-mL for hot water bath

Beaker, 400-mL for rinsing stirring rodsStirring rods

Ring stand, ring, wire gauze, burnerCorks to fit test tubes

Beral pipet, graduated (optional)pH paper or litmus paper

Centrifuge

Procedure

Safety Alert

Most of the acids and bases used are very concentrated and can cause chemical burns if spilled. Handle
them with care. Wash acid or base spills off of yourself with lots of water. Small spills (a few drops)
can be cleaned up with paper towels. Larger acid spills can be neutralized with baking soda, NaHCO3,
and then safely cleaned up. Neutralize base spills with a vinegar solution (dilute acetic acid). Some of
the compounds are poisonous. Wash your hands when finished.

Solutions containing silver ions and potassium permanganate solutions cause stains which do not appear
immediately. If you suspect that you spilled any of these solutions on yourself, wash off with soap and
water.

Wear Chemical Splash Goggles and a Chemical-Resistant Apron.

Preparation of a Solution for Analysis.

Prepare a known solution containing 1 mL of each of the anions to be tested. This solution will be
referred to as the original test solution.

Your teacher will provide you with an “unknown” solution to be analyzed.

Note that the following directions are written for a “known” solution that contains all of the anions. An
“unknown” solution will probably not form all of the products described in this procedure. You should
make note of any differences as you analyze your “unknown” solution.

Aqueous solutions of all of the anions to be tested are colorless. The positive ion associated with each
of the anions will be either sodium or potassium ion.

1. Separation of the Halides (Cl-, Br-, I-); Confirmation of Chloride.

The halides all form insoluble silver compounds. Silver chloride is a white solid, silver bromide is...
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