[n2ro]

Hi There,

I have a bit of a problem I'm stumped with regards to the Gravimetric Determination of Sulfate. So here's the process & problem

Start by precipitating out the sulfate with a barium chloride solution, over heat. The precipitate is then filtered out into an ashless filter paper, put into a crucible, and the paper is burnt off. The mass of the barium sulfate is then taken (minus crucible).

The lab is very similar to this one http://www.csudh.edu/oliver/che230/labmanual/gravsulf.htm and is pretty standard first year stuff.

Over three lab sections, the amount of sulfate determined was on average 15-20% below what we know is in the sample.

I've checked all the stock solutions, Na2S04, BaCl2, HCL - and ensured they are at the right concentrations.

What could be causing such a loss of sulfate? Any suggestions would be appreciated!

Thanks!

[Borek]

First thing I can think of - reduction of sulfate to sulfide by the carbon from the filter paper?

I know it can be a problem, but it would be rather surprising if you will get reproducible result.