Analysis of Zinc in Pickling Acid  using the Dropper Bottle Method              

1.0   Purpose

1.1   To provide quick, reliable in house test results.

2.0   Reagents

2.1    ZINC TITRANT:  E.D.T.A. ( C₁₀H₁₄O₈N₂Na₂ * 2H₂O ) F.W. 372.24 

2.2   ZINC BUFFER :  Ammonium Hydroxide ( NH₄OH) 26 degree baume.  Ammonium Chloride   ( NH₄Cl)  M.W.  53.49.  Read MSDS before using.

2.3   ZINC INDICATOR :  Erichrome Black T, absolute ethanol and triethanolamine.

3.0   Procedure

3.1   Use 0.1 ml sample of acid and transfer into 60 ml shaker bottle.

3.2   Add 40 ml of distilled water to bottle

3.3   Add 5 ml of zinc buffer to bottle.  Shake well until green liquid turns to orange/brown.

3.4   Using medium filter paper, filter the orange/brown solution. Then use the clear solution for the zinc titration.  Small amounts of distilled water can be used to was down the filter paper.

3.5   Add 1-2 drops of  zinc indicator to the titrating  beaker. Solution should be wine-red in color.

3.6   Titrate sample using titrant (E.D.T.A.) in the calibrated dropper bottle from wine -red to blue endpoint.   Keep track of the number of drops to determine amount of zinc.

4.0   Calulations  ( Specific gravity of acid assumed 1.3 g/ml)

4.1   For a 0.1 ml sample multiply  the drops used to change the color from wine-red to blue by   0.5 % wt.