Sciencemadness Discussion Board

Concentration of BaCl2 by Common ion efect

RU_KLO - 21-3-2024 at 15:30

Im converting PbSO4 into H2SO4 by HCl as an experiment.

As I have the PbSO4 and HCl mixing and heating, a question in my head was how to confirm if H2SO4 was made and if possible how much, because it wll be mixed with HCl. (plus PbCl2 and PbSO4)

So I made some side experiments,
1) To add some random amount of PbSO4 in a test tube, add some water, shake, decant and filter.
To the filtrate add BaCl2 solution (of unknown strenght) and see how much precipitate I got (which it was not much - because of low solubility of PbSO4, but there is some turbidity.

2) Add some BaCl2 to the HCl (aprox 6M), and when Idid it, noted (did not expected) some precipitate was formed. After checking, it was because of the Common ion efect. (BaCl2 precipates on adding HCl to a BaCl2 solution)

So the question is: If I know the strenght of the acid (10ml 5,8M HCl), the ammount added of BaCl2 sol. (2ml) and the weight of the precitate (after filtering, drying) , lets say 0,01 mg.
Can I get the concentration of the original BaCl2 solution? How?


As side note: I "know" that better is to use H2SO4 to transform to BaSO4 and then weight it. and then calculate it.
How should I proceed?
For example:
take 10ml of unknown BaCl2 sol.
add dropwise H2SO4 (1 Mol for example - does concentration of H2SO4 matter?) until nothing more precipitates.
filter, dry, (maybe ignite) the precipitate. Weight.

Now from the weight of BaSO4 how I get to BaCl2 concentration?


Thanks



bnull - 22-3-2024 at 06:15

I came across a work done by an Indian (from India) chemist, B. P. Choudhari, about the exact same experiment you're doing. He wrote two papers, of which I have the second (it may interest you, see attachment). The first was co-written with A. N Kappanna and is nowhere to be seen. It seems that sulfuric acid is produced only if the concentration of hydrochloric acid is above 7%. The details are probably in the co-written paper that, again, is nowhere to be seen. (If you can find it, please send me a copy. I feel like reading a novel missing the first half.)

Attachment: 947-948.pdf (152kB)
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Quote: Originally posted by RU_KLO  
So the question is: If I know the strenght of the acid (10ml 5,8M HCl), the ammount added of BaCl2 sol. (2ml) and the weight of the precitate (after filtering, drying) , lets say 0,01 mg.
Can I get the concentration of the original BaCl2 solution? How?

Try this: Solubility Product Constants. Don't forget to adjust the HCl concentration (it goes from 5.8 M in the original solution (10 mL) to 4.83 in the mixed solution (12 mL)).
Quote: Originally posted by RU_KLO  
As side note: I "know" that better is to use H2SO4 to transform to BaSO4 and then weight it. and then calculate it.
How should I proceed?
For example:
take 10ml of unknown BaCl2 sol.
add dropwise H2SO4 (1 Mol for example - does concentration of H2SO4 matter?) until nothing more precipitates.
filter, dry, (maybe ignite) the precipitate. Weight.

Now from the weight of BaSO4 how I get to BaCl2 concentration?

Let's say the precipitate weighs 233,39 mg (233.39*10-3 g). Divide the mass of the precipitate by the molar mass of BaSO4 (233.39 g/mol, according to the CRC Handbook 97th). It gives the number of moles of barium sulfate in the precipitate, which is conveniently equal to 10-3 mol in our example. It is the same quantity in moles of barium or Ba2+ in the precipitate (because there is only one Ba2+ in each BaSO4). Divide this by the volume of the solution (10 mL, or 10-2) and you'll have the concentration of BaCl2in moles per liter. In our example, it gives 0.1 mol/L.

A tip: you may add ethanol or isopropanol (this one's better) to the solution after you stopped adding sulfuric acid. Alcohol helps precipitate BaSO4 from the solution if you want an even more precise measurement of the concentration.

[Edited on 22-3-2024 by bnull]