Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Kosan8095 on February 17, 2021, 12:13:26 AM
-
Hello,
I am writing this forum post because I am dealing with a great deal of confusion concerning a research project I have to do for CEGEP(after high-school but pre-university in Québec, therefore I am posting this in the undergraduate section as I think I am technically studying an undergraduate biology course). I have to measure the effect of Water hyacinth (rhizofiltration) in the removal of heavy metals or contaminants in an aqueous solution. Wether or not it actually works doesn't really matter. I chose Lead as the metal that I have to measure. However, to my great dismay, my school lab does not have any of the fancy spectrophotometry equipment to measure the concentration of lead (mg/L) in an aqueous solution. I want to ask the chemistry forum for alternatives methods that will work on determining the concentration lead in a solution (<1g/L) that doesn't require spectrophotometry analysis. I just have to prove that concentration before the aquatic plants are introduced (I will let them sit on a lead solution for 72h) is less than (or unchanged) the concentration at the start. I can also do the expriment with many other heavy metals such as copper(Cu), chromium(Cr), nickel(Ni) or zinc (Zn) if there are ways to determine concentration in a solution for these metals rather than lead.
I'd like to express my most sincere gratitude towards the people who offered their precious time to read this lengthy and stubborn post of mine.
Sincerely,
Kosan8095(my pseudonym)
-
Do you have any thoughts after reading WIKI
https://en.wikipedia.org/wiki/Quantitative_analysis_(chemistry) (https://en.wikipedia.org/wiki/Quantitative_analysis_(chemistry))
-
An idea (not sure if it's feasible in practice): Find a reaction that causes the lead to precipitate, filter off the aqueous layer and dry the precipitate, then weigh it and calculate the mass of lead in the precipitate. I'm not a chemist (yet), so there might be easier ways to do it.
-
An idea (not sure if it's feasible in practice): Find a reaction that causes the lead to precipitate, filter off the aqueous layer and dry the precipitate, then weigh it and calculate the mass of lead in the precipitate. I'm not a chemist (yet), so there might be easier ways to do it.
Won't work for ppm levels.
Electrochemistry and spectrometry are the best methods here, but they require proper hardware.
-
Could they measure current flow or voltage on a sample water spiked with lead or copper against standards they have made? I could see a device like this being home made with a voltmeter or ammeter. The OP says the accuracy does not have to be perfect for the class project.
-
... Wether or not it actually works doesn't really matter. I
...
I just have to prove that concentration before the aquatic plants are introduced (I will let them sit on a lead solution for 72h) is less than (or unchanged) the concentration at the start. ...
...
Won't work for ppm levels.
...
Since, according to OP, accuracy is not as important as direction of measurement for this HS school project, could weighing be enough.
-
Since, according to OP, accuracy is not as important as direction of measurement for this HS school project, could weighing be enough.
No, most likely OP would get zero for all samples.
-
Depends on sensitivity of the balance, amount of lead in solution, and the volume of solution assayed. As a back of the envelope calculation, let's say you have 1 gram (1 mL) of solution. A concentration of lead at 1 ppm (1 g lead/1 million g water), would have a mass of lead of 1 ug. Granted, it'd be coordinated with something else that will have mass, so let's be generous and call it 2 ug of precipitate. If your sample volume were 100 mL, and assuming 100% recovery, now we're talking 200 ug mass of precipitate. Do you have a balance that can discriminate 200 ug from background? If not, method isn't feasible for 1 ppm level detection. Moreover if you know the sensitivity of your balance, you can back-calculate the expected approximate detection limit for a gravimetric detection of lead using your balance. 10-100 ug pushes the sensitivity of even high quality analytical balances, so, the method isn't ideal for trace analysis, and this doesn't even get into possible interferences by other metals that can precipitate. But if your concentrations are in the 100s or ppm so that your precipitate mass is a few mg, then maybe you could get a semi-reliable value.
-
As an aside for more info
I did some GOOGLE on how lead can pollute water
Lead Solubility
https://www.sciencedirect.com/topics/engineering/lead-solubility (https://www.sciencedirect.com/topics/engineering/lead-solubility)
Toxicological Profile for Lead
https://www.ncbi.nlm.nih.gov/books/NBK158769/table/T15/ (https://www.ncbi.nlm.nih.gov/books/NBK158769/table/T15/)
Assessing the Lead Solubility Potential of Untreated Groundwater of the United States
https://pubs.acs.org/doi/10.1021/acs.est.8b04475 (https://pubs.acs.org/doi/10.1021/acs.est.8b04475)
Compounds of lead
https://en.wikipedia.org/wiki/Compounds_of_lead (https://en.wikipedia.org/wiki/Compounds_of_lead)
Lead Compounds - US EPA
https://www.epa.gov/sites/production/files/2016-09/documents/lead-compounds.pdf (https://www.epa.gov/sites/production/files/2016-09/documents/lead-compounds.pdf)