thunderfvck - 1-10-2004 at 08:22
Hello!
I just finished a lab. I was wondering about something.
We had to titrate two solutions with two different indicators.
One of them gave the concentration of Mg(II) and Ca(II) ions, the total of them. The other gave the concentration of only the Ca(II) ion.
Now, it was simple. I found the total, and subtracted the Ca(II) ion to get the Mg(II) ion. And so I had both concentrations.
I found the moles of Mg(II) and Ca(II), we'll call it x. And the molarity of Ca(II) was y. So, x-y = moles of Mg(II). Then I divided them by
their volumes and found the concentration of each. Sounds good, right?
Well on the handout that was given, it had asked me to find the concentration of both. So I added the concentrations of each individual ion I found,
is this the proper way to do it? I think it is.
But it had asked me to find the total concentration after having found the molairty of both ions. Are you able to do this, when it has to be in g/L
rather than mol/L? Can you add the two molar masses of the ions and use this as your molar mass, and then divide it by the volume to find the total
concentration? This doesn't seem right to me but this, apparently, is how the procedure had instructed me to do so. But I neglected this and went
ahead with finding each molar quantity and finding the concentration of each independently, and then added the two.
So which is it?
Thanks duders!
Magpie - 1-10-2004 at 17:42
I think you are correct in adding the molarities.
If you are 3 molar in Ca++ and 1 molar in Mg++, then I think you are correct in saying that you are 4 molar in Calcium+Magnesium.