Make solution of Pb2+ , suspend in broad testtubes or 100 ml flask( since precipitate ekll be easier to see) and vary their pH over a wide pH range. Say 2-10 with a difference of 1 pH unit. At some point u will see precipitates in the test tube or flask. Repeat with pH tube/flask of 1 lower, same and higher pH. To confirm precipitation pH.
Carry out the experiment of adsorption following this.
Alternatively you can search literature.
** precipitate will be easier to observe in broad testtube or 100 mL flask.
You must calculate the precipitation ph from ks of pbOH2 and concentration of pb2 +
Thanks Fatima but how do I calculate precipitation pH from Ks of Pb(OH)2 and concentration of Pb2+?
John Godwin Solubility of lead in water is dependent on the compounds used its valency and other anions present. Oxides and sulfides of Lead, chlorides, Nitrates, and Hydroxides of Lead have different solubilities at different pH.
You can use an indirect method.
Estimate total metal content as the lead oxide by gravimetric method. ( You can also use AAS to estimate Lead)
1. Prepare the biosorption solution containing Lead. Filter through 0.22-micron filter. Estimate total lead as Total fixed solids (TFS) (as the lead oxide by volatilizing the solution at 550 deg centigrade in muffle furnace).
Claculate= Total Lead added by Weighing - Actual Present in TFS/AAS
Reason: Soluble lead and insoluble (precipitated) in the sample solution prior to the biosorption experiment can be known.
If needed quantitatively estimate by AAS ( Solubilize the minerals in Sulfuric acid and Estimate by AAS)
2. Perform the biosorption experiment with the desired agent. Decant solution from adsorbing matrix.
Perform TFS/ AAS of Filtered and Unfiltered solutions.
The difference between the two is that precipitated lead in the solution is which is not accessible for biosorption.
3. Also Perform TFS of Biosorbant and Estimate lead to confirm actual biosorption.
If you want to dertermine the pH-dependent precipitation you can do a pH-titration. If the Hydroxide is fromed the pH reaches a plateau, where the OH is consumed by the metal for the formation of the metallhydroxides.
An other possilibity is the solubility product. For lead you can calculated a pH of 8.7 for the precipitation. But the precipitation will start earlier. Lead as a precipitation pH-range of 7.2-8.7, this you can also see in the pH-titration curve.