[fobbz]

An impure barium chloride sample weighing about 0.40 g was dissolved in water and then treated with excess sulfuric acid. Calculate the volume of 4.0 M H2SO4 needed to completely precipitate the barium ions as barium sulfate, BaSO4. (Give your answer to 2 significant figures.)

So to start off this problem I found the moles for Ba²⁺ in BaCl₂ Ba²⁺ + 2Cl^-

to be 0.001921.

I then took the molar concentration of SO₄^2- to be 4.0M, and solved for the volume in mL by going like this

x L = (0.001921mol Ba²⁺)/(4.0M)

The answer in mLs I get is 0.48, rounded to 0.5mLs.

What am I doing wrong here? Please help.

[Borek]

0.5 has one significant figure.

[fobbz]

It might, but it 0.48ml which was the number not rounded is still not the answer.

[Borek]

I got 0.48 mL as well.

Technically speaking you should use some excess to be sure barium was completely precipitated. But I doubt question requires you to use solubility product and evaluation of solubility.