Question

titration help

Answer 1

if you titrate 25.00 ml of 0.03080 M Na2CO3 with 0.02560 M Ba(NO3)2, net ion equation is Ba2+(aq) + CO32-(aq) -> BaCO3(s). Find the pBa2+ after 10.80 ml of Ba(N03)2 are added when Ksp=5.0x10 ^-9

Answer 2

this question has me stuck and my exam is coming in 3 days :(

Answer 3

What do you mean by pBa2+? Concentration of Ba2+?

Answer 4

p is the negative log, i think he means -log(Ba2)

Answer 5

Ok

Answer 6

for Ba2+ i got 0.000276 mol
for CO23- i got 0.00077 mol

do i subtract and then divide by total volume to get [CO32-]?
I think i did this
\[Ksp = \frac{1}{[Ba^{2+}][CO_3^{2-}]} \rightarrow [Ba^{2+}]=\frac{1}{Ksp[CO_3^{2-}]}\] is that correct??
but my value is -10.16, and i dont know if that is correct answer.

Answer 7

Oh ok let me just work through it and I'll let you know. I got the same values as you for moles.

Answer 8

Yes I think that is correct. Hopefully there's someone else around who can verify the answer as it's been some time since I've done these problems...

Answer 9

well, I used only moles to find pBa2+ and i got 3.30 which is more reasonable but i dont know if that is correct. i did not take volume into account since i form a solid?

Answer 10

No for pBa2+ you need to use concentration. Just because it's negative doesn't mean it's unreasonable. Theoretically you could have negative pH (which is maybe why you think your negative answer doesn't make sense).

Answer 11

yes but -pH for solution i was given does not make sense i dont think Ba2+ makes sense for negative pH, yes?

Answer 12

I don't quite understand your question - in practice you can't really get a negative pH due to limitations of measuring equipment, but in theory it's possible to calculate it if your solution is extremely concentrated. I don't see why the same wouldn't be true for Ba2+

Answer 13

i think i understand you. so is what i found ok for pBa2+?

Answer 14

I would say so. Like I said though, it might not be a bad idea to run it by someone else.

Answer 15

ok, thank you :)