#1 Science Forum For Lab Technicians

This prac from Chemical syllubus p59 alaways yeilds poor results is there a way to improve this?

If it is the one I am thinking of, we use epsom salts. What do you use? The silver nitrate has to be fairly diluted (i think .001M), but that might be for a different prac done about the same time...

Hi there,
Are you doing the experiment where you add BaCl2 to precipitate out the BaSO4? The problem we have is hoping the particles are large enough to filter out. We use sintered glass crucibles on flasks attached to venturi pumps. Last year we had good results, but I noticed the word HOT written next to 5% BaCl2. I know the whole thing has to stew for a while before filtering.
Hope this helps.
Cheers, Ellice.

Ellice, do you use epsom salts for the fertilizer?
Lada

I'm not sure, but didn't someone post a titration prac as an alternative to achieve the same results?
Regards,

We used to do titration prac, but the HSC question always refer to gravimetric, so we switched and use BaCl2 to precipitate the SO4 as BaSO4
We use hand operated vacuum pumps to filter as the ppte is very fine.
Lada

Gotcha! Now I understand why the teachers here didn't like to use that option! Boy! I tell you, if it wasn't for this site, I'd still be using a white cane!
Thanks,

Hi Lada,
We use a fertiliser from Bunning's. I just had a look, and it's 'Sulfate of Ammonia'. It has the %SO4 on it. Never tried Epsom salts.
Cheers, Ellice.

We have just had an absolute debarkle trying to get this experiment to work.

I made about 6 trips to the store cupboard as the teacher decided to try different things,
I got buchner funnels in2 different sizes, gooch crucibles in 2 sizes, side arm flasks and water powered venturi pumps, centrifuge and desicators !!!!!!!!!!!!!!!!!!!!!!!!!!!!!( the silica gel is finally blue again)

We have 2 year 12 Chem classes, yesterday the teacher used rather small amounts and the centrifuge, today the teacher had about 250 mls he wanted to filter the precipitate out of.

Has anyone had any sucess in working out the best volumes to use ( we were using bariium nitrate 0.2M and a made up fertiliser of ammonium sulphate and suger) and the best method of filtration. I have special filter paper (grade 333 glass microfibre filter paper but it is only 47mm diameter bought initially to fit the goocg crucibles but wat too small for the buchner funnels)

Also does it work better with barium chloride 5%. My thought was it wouldnt make much difference as the problem is in separating the barium sulfate so it can be weighed.

Any suggestions?

Wendy

Hi Fibreweb
We have 2 classes yr 12 who do it every year. I got the proper filter paper for filtering Barium sulfate for the Bruchner funnels and etc, etc.........and it still doesn't work properly!
Our teachers have become philosophical about it - they do it as an exercise to show how it should be done and what goes wrong......
Sorry can't help more.
Regards
Sue G

In a former life when determing sulfate concentrations, we did it turbimetrically. (i.e. form the barium sulfate ppt and then measure the turbidity against a range of std solutions). This way we didn't have to worry about filtering.

definition ....."Turbidity is cloudiness or opacity in the appearance of a liquid caused by solids, particles and other polutants. "

BaSO4 is more a suspension than a ppt. does it specifically state you need to filter and determine gravimetrically??

We had a turbidity meter that didn't seem very fancy so don't know how much it cost, but basic turbidity readings can be taken with a glass/plastic tube - we do turbidity measurements for waterwatch.

I'm at a 7-10 school so i haven't come across this prac. sorry I'm not more help.
Shas