NaSR/Na2S

Question 1

Preparing Sample

Answer 1

• Place 300 mL plastic beaker on balance and rare
• Pipette between ~1-5 grams of caustic into beaker and record weight
• Add 125 mL of Sulfide Solution to weighed beaker
• Use NaSR electrode, examining it to verify silver coating intact. Analyze a sample containing Na2S or NaSR with sulfide solvent. Rinse w/DI water and blot dry with clean, soft tissue
• Titrate w/ 0.01N Alcoholic Silver Nitrate

Question 2

Program Instrument

Answer 2

• Load Tiamo software (if closed type in LAB for user)
• Click Workplace icon in left side of screen
• Select Single Determination tab
• Enter information in for Mass, AgNO3 normality, and Sample name
• Hit Green start button
• When analysis is complete, rinse electrode w/ DI water, blot, and replace plug and out electrode in storage solution

Question 3

Purpose of Test Na2S/NaSR

Answer 3

Method is for analysis of used refinery caustics for concentration of sulfur present as sodium sulfide and sodium Mercaptide. Sample dissolved in alcoholic sodium hydroxide with 1% ammonium hydroxide, then potentiometrically titration with alcoholic silver nitrate solution. Amount of Na2S or NaSR in caustic determines degree of spent or regeneration of caustic.

Question 4

Data Analysis

Answer 4

• After analysis, click Database icon
• Right click desired sample analysis and select Reprocess
• The Curve Evaluation tab is very important and is only PLACE THAT SHOWS THE DERIVATIVES of the curve (edit if necessary)
• Endpoint for NaSR is typically in -250 to -350 mV range. Endpoint for Na2S is typically in +100 to +300 mV range

Note** To determine Na2S is present, dip lead acetate paper into caustic. If it turns silver-black, test is positive and sulfide ions present. Some mercaptides will turn acetate paper tan or yellow. This is not positive for sulfide test.

Question 5

Calculations

Answer 5

For one Endpoint
•NaSR = (3.2 x Norm of AgNO3 x Endpoint 1)/(Sample Weight)

For two endpoint
•NaSR = (1.6 x 2 x Norm of AgNO3 x (Endpoint 2 - Endpoint 1)/ (Sample Weight)
•Na2S = (1.6 x Norm of AgNO3 x (Endpoint for Na2S) / (Sample Weight)

Question 6

Troubleshoot/Maintenance

Answer 6

Titrate:
•Verify correct tires to in use, and enough Titrant is available for analysis
•Verify no air in line and no cracks or leaks in line

Question 7

Sulfide Solution

Answer 7

Add 4.5 L of NaOH, 4.5 L of 2-propanol, and 180 mL of NH4OH to container and purge w/ nitrogen for 1 hour