Processing kodak motion picture films, module 3 analytical procedures

Procedure for Electroplating a Silver-Silver Iodide Electrode
900
INTRODUCTION
Current development work for the determination of
potassium iodide in developers showed a problem when the
silver electrodes were cleaned to brightness. Subsequent
titrations after cleaning yielded low answers due to aerial
oxidation of the electrode when used for a silver nitrate
titration of potassium iodide. The problem is more
pronounced at low levels of iodide (0.25-2.00 mg/L KI). The
electroplating procedure should be used whenever an
electrode is first used for a silver nitrate titration of iodide,
regardless of the iodide level. The electrode should not be
recleaned and replated between titrations but simply rinsed
with distilled water and wiped dry. It can be stored dry or in
distilled or deionized water
APPARATUS
Silver Bar or Silver Billet Electrode
Dry Cell, 3-6 volts (e.g. Burgess No. 5156, 22 1 ⁄ 2 volt)
REAGENTS
For instructions on the preparation of the required analytical
reagents see Module 4, Reagent Preparation Procedures.
50 mg/L Potassium Iodide
Aluminum Wire, 20 gauge, Reagent Grade.
PROCEDURE
1. Thoroughly clean a silver electrode with an abrasive
cloth or household cleanser. Rinse well with distilled
water and wipe dry.
Note: If powdered cleanser has been used, make sure
any adhering cleanser is removed from the electrode.
If it is allowed to remain, it will prevent even plating.
2. Prepare a 50 mg/L potassium iodide solution by
dissolving 50 mg of reagent grade potassium iodide in
distilled water and diluting to one litre.
3. Add about 300 mL of the 50 mg/L potassium iodide
solution to a 400-mL beaker. Enough solution should
be added to completely cover the silver metal section
of the electrode, while it is being held about one inch
from the bottom of the beaker. Do not immerse the
electrode yet.
4. Connect a 6-inch piece of reagent grade aluminum
wire to the –3 volt terminal of a dry cell. Immerse
about 2 inches of the wire into the solution in the
400-mL beaker.
5. Connect the electrode lead to the positive terminal of
the dry cell.
6. While stirring gently, immerse the electrode in the
potassium iodide solution for approximately three
minutes. After three minutes, remove the electrode
from the solution and rub dry with a tissue.
7. Repeat step 6 six times.
Note: There should now be a smooth even coating of
silver iodide on the electrode. If bare spots are
apparent, the electrode should be recleaned and
replated according to this procedure.
8. When satisfactorily plated, the electrode needs only to
be rinsed well with distilled water and wiped dry
between titrations. It can be stored dry or in distilled or
deionized water.
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 1