Reaction between barium and sulphate?

ASidd

We did an experiment in class today with Barium and sulfate.
To one of the experiments we added a couple of drops of HNO3 to make it acidic and to the other one NaOH to make it alkaline.
the barium and then sulfate
The only one where they both reacted to make a precipitate were the acidic solutions

So I want to know that is this a known fact that Barium will only react with Sulfate under acidic conditions? Why?

aroc91

When you have a metal in the presence of an acid, you'll see that a gas is produced. This is hydrogen gas from the H+ reacting with the metal, stripping it of electrons, forming H2, and producing soluble oxidized metal ions.

Oxidizing barium metal results in soluble Ba2+, which then reacts with the sulfate. Under basic or neutral conditions, there is nothing to strip electrons from the barium so it will remain undissolved and no Ba2+ will be present in solution.

ASidd

yes but we had barium in the form of barium nitrate solution and copper as copper sulphate solution.Wouldn't both already be present as ions in solutions?

Borek

Barium is so reactive it will react with water on its own.

I can't think of any reason why barium sulfate would not precipitate in alkaline solutions.

ASidd

yes but we proved that it doesn't.
Is there a reason for the reaction occurring at a low PH

Borek

What salts were used in the experiment? Do you know concentrations of reagents used?

In high pH barium can be slightly complexed by OH^- anions, but the stability constant is so low (around 0.6) it should not change anything. Ba(OH)₂ itself is weakly soluble (Ksp values - 3.6 for hydroxide and 10 for sulfate) but you say you have not observed any precipitate at all, so it doesn't matter as well.

Strange result.

ASidd

We used barium nitrate solution and copper sulphate solution. About 10drop each. Then 5 drops of the acid or alkali.

It was a simple precipitation reaction.

ASidd

The concentration would be about 0.1 mol

aroc91

Oh, duh. I was thinking it was a transition metal for some reason. Disregard me.

Borek

And you have not seen a copper hydroxide precipitation in the alkaline solution?

lightarrow

Maybe it has to do with the electrical charge of the solid BaSO₄ particles initially formed. I know that in some cases, particles that will form a precipitate, have initially an electrical charge which depends on which one between cation or anion is more absorbed by the particles. Maybe, but I'm just speculating, BaSO₄ particles absorb SO₄^2- in eccess, becoming negatively charged, so adding H⁺ could reduce this charge and favour their coalescing into a solid precipitate, while OH^- ions could prevent this coalescence.