SolderOn Tin (SnII) Analysis

Equipment Required:

• Titration flask (125 ml)
• 10 ml Automatic pipette
• Digital titrator
• 0.5 gram measuring spoon

Reagents Required:

• Iodide-iodate standard titration cartridge
• Hydrochloric acid, conc., ACS
• Sodium bicarbonate, ACS
• Starch indicator solution

Procedure:

1. Measure 30 ml of deionized water into the 125 ml titration flask. (Quantity is not critical)
2. Add 1.0 ml of the plating bath using the automatic pipettor.
3. Add 10 ml of CONCENTRATED Hydrochloric acid or 20 ml of 1:1 hydrochloric acid. Swirl to mix.
   
   
   GLOVES, APRON AND FACE SHIELD SHOULD BE WORN
   WHEN HANDLING THE FLASK AND THE CONCENTRATED ACIDS.
4. Heat the flask until it is hot to the touch. This can be accomplished by putting the flask in the curing oven for 5 minutes with the oven set at 100^oC.
5. Add one dropper-full of Starch indicator solution and slowly add one 0.50 g measuring scoop of Sodium bicarbonate. Swirl to mix.
6. Titrate immediately with the Iodate-iodide standard to the appearance of a blue end point. Swirl the flask continuously to assure proper mixing during titration. Record the number of digits (denoted NUMTIN) required to reach the end point.
7. To determine the concentration of Stannous tin ion (SnII) present in the sample, calculate using:
   
   

   Sn(II) = NUMTIN x 0.0297 g/l

   
   or
   
   

   Sn(II) = NUMTIN x 0.0040oz/gal

   
   
8. Assuming that you are using LeaRonal SolderOn Tin Concentrate (STC) with 120 g/l of tin metal, the amount needed to replenish the 38 liter (10 gallon) bath to the optimum point of 16 g/l, is calculated by:
   
   

   STC needed = (540-NUMTIN) x 0.0025 liters

   
   or
   

   STC needed = (540-NUMTIN) x 0.00064 gal

   
   The acceptable range of digital titrator readings is:
   
   

   Acceptable Range Sn(II):	13.0 to 20.0 g/l
   NUMTIN:	438 to 675

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