This method is valid for 20-100mg/l
Principle: sulfate ion is precipitated and weighed as BaSO4. The solution is first acidified with HCL to prevent the precipitation of BaCO3 and Ba(OH)2 and it also aids the larger precipitate crystals.
Take 200ml sample solution, add 2ml conc. HCL in it, heat the solution on hot plate to near boiling, add 100ml of 0.05M BaCl2 to the hot sample while stirring vigorously. Now filter the ppt. to ash less filter paper like wattman 42 or 44. Wash the filter paper with a little amount of deionized water. Weigh the crucible and note down its weight. Put moist filter paper in it and place in the furnace. (check the crucible till the filter paper completely burns). Cool the crucible in the desiccators. Now reweigh the content.
Weight of crucible + filter paper = 34 + 1.1 = 35.1g
Weight of crucible + residue after ignition + filter paper = 35.117g
Weight of BaSO4 ppt. = 35.117g – 35.1g = 0.017g
Weight of BaSO4 ppt. in mg = 0.017 x 1000 = 17mg
Molecular Weight of BaSO4 = 233.4g
Molecular Weight of SO4 = 96.06g
SO4 in mg/l = mg of BaSO4 x 96.06 x 1000
ml of sample x 233.4
= 17 x 96.06 x 1000 = 34.98mg/l
200 x 233.4
Given sample solution contain 34.98ppm of SO4 by using gravimetric analysis.
Impacts of Sulfate Ions
- Environmental impacts: Sulfates increase the acidity of the atmosphere and hence results in acid rain. It causes the scattering of light and effectively increasing the Earth’s albedo (BUSECK & SFAI, 1999).
- Impacts on Human: if someone drinks water that has above 500 ppm of sulfates then after a short time following symptoms will start appearing:
- Diarrhea and intestinal pain (especially in babies)
- Dehydration due to diarrhea
- A slight decrease in normal stomach acidity
- Catharsis in young males
When sulfates are taken in by breathing then it may cause lung irritation but there are no long-term human health effects are expected (WHO, 1996).
Standards of Sulfates:
|Category||Max. limit||Standardizing Agency|
|Drinking Water||500 mg/l||WHO (1993)|
|Drinking Water||250 mg/l||EU (1998)|
|Drinking Water||250 mg/l||USEPA (1994)|
|Waste Water||1000 mg/l||EU (March 2009)|
|Waste Water||250 mg/l||WHO|
|Waste Water||500 mg/l||NEQ’s (1999)|
- Buseck, P. R., & Sfai, M. (1999). Airborne minerals and related aerosol particles: Effects on climate and the environment. Natl. Acad. Sci. USA, pp. 3372–3379, .
- (1996). Guidelines for drinking-water quality. Geneva.
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