[findingneverland]

I've been dealing with this problem my entire day and i still can't find the mistake, so i would really appreciate if someone would help me with this

So if we mix 50mL, 0,4mmol/L of BaCl2 and 200mL, 1*10^(-5)mol/L of Na2SO4, what is the mass of the precipitate? (Ksp=1.08*10^(-10)).


this is how i calculated the problem

BaCl2 + Na2SO4 --> BaSo4 + 2NaCl

n(BaCl2)= 2*10^(-5) mol
n(Na2So4)= 2*10^(-6) mol

the limiting reagent is Na2So4, so n(Na2SO4)=n(BaSO4) and then i got that the mass of BaSO4 is 4.57*10^(-4).

i don't have the result for this problem, i tried to compare my result with others in class but they got 1.83*10^(-3) g or 3.37*10^(-4)g. I'm not sure where did i make a mistake :S

So again i would really be thankful if someone could help me, please.

[Arkcon]

This is going to be a hairy one, because your use of exponents isn't very clear.  I'm going to work on it, my way, from your first statements, and see what I get.  However, you should try to get everything into same units.  You start with millimoles BaCl₂, you should use that unit, and convert only at the end, to moles, then to grams.  You try it that way, and see if you get better results.  And more important, see where you may be screwing up.

*[EDIT]*

At first glance, I suspected your exponents.  A little work by me shows that I was correct, you are way off.  That is 50 ml, of 0.4 mmol isn't 2x10^-5 moles.  Consider: a 0.4 mmol solution would give 0.4 mol, if you had a liter.  But you have 1/20 of that volume. But 0.4/1000/20 is 2x10^-6*, an you're using 2x10^-5.  And you may have made other mistakes, too.

*Incorrect here, see below.

[findingneverland]

the way i was calculatin
50mL=0.05 L
0.4 mmol/L=0.0004 mol/L

0.05 L*0.0004 mol/L=0.00002 mol = 2*10^(-5)

even if i calculate it your way i get the same value :S

[DrCMS]

But 0.4/1000/20 is 2x10^-6

No it is 2x10^-5

[Arkcon]

But 0.4/1000/20 is 2x10^-6

No it is 2x10^-5

Gah.  I must have typed it wrong into Excel.  Srry folks.