8) Sulphite-ion Determination in Wastewater by Iodometric Titration
As we go about our daily lives, it's easy to overlook the impact of industrial activities on our environment. But the truth is, that the wastewater generated by industries such as paper, textile, and food processing can have devastating effects on our ecosystems. One of the most common pollutants found in industrial wastewater.
The Hidden Dangers of Sulphur Compound in Industrial Wastewater
They are a type of chemical compound that can have serious consequences for our environment. When released into waterways, It can deplete oxygen levels, harming aquatic life and disrupting the delicate balance of our ecosystems. Moreover, it can also contribute to acid rain, further exacerbating the problem of environmental pollution.
We take the test material and add a special liquid called iodate-iodide. This solution is like a measuring stick that helps us figure out how much amount is present. As we add the reagent mixture, we also add a tiny bit of starch. The starch acts like an indicator, helping us see when the reaction is complete. When the sulfite ion (SO32-)in the test material reacts with the iodate-iodide, it changes the color of the starch. This color change tells us that the reaction is complete, and we can calculate how much SO32- was in the sample.
Reagents Required
1. Dilute Hydrochloric Acid (HCl)
- 200ml concentrated HCl- 100ml distilled water- Mix and dilute to desired concentration
Purpose: Dilute HCl is used to create an acidic environment for the reaction. It helps to stabilize the starch indicator liquid and ensures accurate results.
2. Starch Indicator suspension
- 5g starch- 0.01g mercuric iodide- 30ml distilled water- Mix and make up to 1L with boiling distilled water- Boil for 3min, cool, and decant supernatant clear liquid
Purpose: The starch indicator suspension is used to detect the presence of iodine in the reaction mixture. When iodine is present, the starch mixture turns blue-black, indicating the endpoint determination.
3. Standard Iodate-Iodide mix
- 0.713g potassium iodate- 150ml distilled water- 7g potassium iodide- 0.5g sodium bicarbonate- Mix and dilute to exactly 1L with distilled water
Purpose: The standard iodate-iodide diluent is used as a titrant to react with the sulphite ions in the specimen. The accurately known concentration of this solution allows for precise calculation of the SO32-concentration in the sample.
Sampling Precautions
Since sulfites are prone to oxidation when exposed to air, it's essential to exercise great care during sampling. Follow these steps:
1. Collect the specimen by allowing 8-10 times the volume of the 250ml bottle to run to waste before taking it.2. Run it to the bottom of the 250ml bottle.3. Handle the bottles carefully to avoid agitation, which can cause oxidation of sulphites.
Preparation of Sample
1. Measure 2ml of dilute hydrochloric acid (HCl) into a 350ml porcelain basin.2. Add 100ml of the test portion.3. Add 1ml of starch indicator.
Analysis Procedure
1. Titrate the Analyte immediately with standard iodate-iodide diluent.2. Stir the mixture continuously during equivalence point determination.3. Continue titration until a faint, permanent blue color is obtained.4. Handle the burette and titrant carefully to avoid errors in measurement.
Handling Skills for Better Accuracy
1. Use a clean and dry burette and titrant to avoid contamination.2. Handle the Analyte and reagents carefully to avoid spills and errors.3. Use a calibrated pipette to measure accurately.4. Stir the mixture continuously during titration to ensure uniform reaction.5. Use a stopwatch or timer to record the time of reaction completion accurately.
Potential Causes of Failure of Analysis
1. Contamination of the test portion or reagents.2. Inaccurate measurement.3. Failure to stir the mixture continuously during determination.4. Inadequate calibration of the burette or pipette.5. Presence of interfering substances
Calculation:
- Sulphite (SO32-), mg/l = 8 V
- V (ml)= Std iodate-iodide solution volume consumed.