[justinh8]

I need some help with this question, What is the concentration of all ions after 600.0mL of 2.00 mol/L Barium nitrate is added to 100.0 mL of 2.50 mol/L sodium phosphate.
What I did was i first found the mols of both substances and from there i have no idea what to do.
Please explain, Thanks!

[Arkcon]

OK, you've made a good first step.  Now, you've figured out moles of substances, but the question asks for ions.  If you've mixed both substances in water, how many ions do you get.  Careful now, mixing might change things, this is chemistry, not doing sums.

[justinh8]

Can you show me what to do, i found the LR now and i found the mols leftover, What do i do now???

[Sophia7X]

Did you write the balanced equation for this? You should get a precipitate.

Use the LR to determine how many moles of precipitate is formed.
Then figure out the moles of the individual ions (make sure you look at subscripts! For example Na3PO4. You have 0.25 moles of that but since you have 3 sodiums, you have 0.75 moles of Na+).

Then you take the moles of Ba+2 (from Ba(NO3)2) and subtract by the amount of Ba+2 in the precipitate (to find how much excess ions you have).

PO₄^-3 completely reacts because it is part of the LR (Na3PO4). So the concentration of that ion is 0.

Na and NO₃^- are spectators so their concentrations are unchanged.

Once you find the mole amounts of each ion, don't forget to divide them by the total volume because the question asks for the concentration (molarity).

Total volume is just 600 mL + 100 mL = 700 mL