High Sulfide Concentration In Water

Question 1

Intro to equipment

Answer 1

• water sample added to mixture of iodine and hydrochloride acid.
• Acid used to free up sulfide.
• Portion of iodine used in oxidation of sulfides
• Using starch as indicator, mixture is titrated w/sodium thiosulfate and excess iodine concentration is determined.
• quantity of sulfides is proportional to quantity of iodine

Question 2

Procedure for samples

Answer 2

• in 250mL Erlenmeyer flask, add 25 mL of 0.1 N iodine
• Pipette 5 mL of 1:1 or 50% Hydrochloric Acid below surface of Iodine and swirl to mix
• Add appropriate amount of water sample below surface of liquid and swirl (appropriate amount found in hood)
• if iodine color disappears when sample added, add more iodine so color remains. Record total volume of iodine used
• while swirling mixture Titrate w/0.1 N sodium thiosulfate until sample is faint yellow in color (almost to endpoint)
• add starch indicator and gently mic until solution black in color(~0.5mL)
• continue to Titrate w/0.1 N sodium thiosulfate until color changes from black to clear or milky white
• record total volume of 0.1 N sodium thiosulfate

Question 3

Procedure for Blanks

Answer 3

• in 250mL Erlenmeyer flask, add 25mL of 0.1 N iodine
• Pipette 5mL of 1:1 or 50% Hydrochloric acid below surface of iodine and swirl to mix
• add 4-5 drops starch indicator and mix
• Titrate with 0.1 N sodium thiosulfate while swirling
• record amount of sodium thiosulfate used (should be close to 25mLs)

Question 4

Troubleshoot

Answer 4

• cap dispensers when not in use to minimize air in line
• dispense small amount of iodine, Hydrochloric acid before starting to verify air not in line
• verify correct reagents used
• recheck all calculations

Question 5

Purpose

Answer 5

Determine concentration of H2S in refinery process waters. Presence of sulfide in waste waters comes, in part, from bacterial decomposition of organic matter and from industrial wastes, but largely from bacterial reduction of sulfate. H2S escaping into air from waste waters containing sulfide is highly toxic. Also very corrosive to metals and concrete when it becomes oxidized biologically to sulfuric acid.