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## Chemistry Help (note somewhat advanced)

[COLOR=Wheat]OK, well I'm in gen chem 2 in college, but since I placed out of the class, I only have to take the lab. It has been a good year and a half since I have done any inorganic chem, so I'm kinda rusty.

I have done the work, now all I am looking for is someone who is somewhat more advanced than myself to tell me if I am thinking along the right lines. If I am not, then I would appreciate a nudge in the right direction. :innocent:

k, here are the two questions.

1) We performed a complexometric titration, involving EDTA. The unknown solution contained H+, and so before we titrated the unknown solution with the EDTA (to find out the concentration of other ions in the solution [magnesuim and zinc]), we neutralized the H+ by adding a perdetermined amount of NaOH. Also, the solution was buffered to pH10, so that the Mg and Zn would form the complex more easily.
The question is, why was the acid neutralized?

Answer: if the acid were not neutralized, then the pH would have been significantly lower, which means that the complex may not have been able to form.

2) The capacity of an ion exchange resin is usually expressed on the basis of the number of 'milliequivalents' of charge that can be exchanged per mL of the resin bed. If a packed column with a capacity of 3.5 milliequivalents/mL of resin has a total resin volume of 15.5mL, what is the maximum number of millimoles of Ca2+ that could be exchanged before the resin is saturated?

(3.5 * 15.5) / 2 = 27.125 millimoles of Ca2+.

The
(3.5*15.5)

gives you the total amount of charge that can be stored, and then you divide by 2, because each millimole of Ca2+ has a charge of 2.

Does this sound right?
Thanks for your help if you can indeed help. peace :teeth:

EDIT: ok, ill just go finish my differential equations homework, read the italian play, and then come back and see whats going on... what i would give for it to be friday, there to be a bottle of captain morgans rum by my side, and a party with hot girls to go to... ahhhhhhhhhhhh[/COLOR].

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[color=#0080ff]say hello to my little friend...[/color]

[color=#0080ff].... mixedvariety, he's your man :cool:[/color]

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When tintrail's question gets answered, I'm going to need some help with my linear control systems engineering. Or perhaps my aerodynamics classes...

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im scared. i think high school chemistry is hard.

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Originally Posted by Jigga-Scrooge
im scared. i think high school chemistry is hard.
AP or CP? CP is cake. AP is hell.

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Originally Posted by AeroJonesy
When tintrail's question gets answered, I'm going to need some help with my linear control systems engineering. Or perhaps my aerodynamics classes...
You doing aerospace? I am. Why is my low speed aerodynamics book completely written in calculus? The cover looked so cool, but when I open it up, its just lines and lines and lines ...... *gets dizzy and falls asleep*

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Originally Posted by Wuhan_Clan
You doing aerospace? I am. Why is my low speed aerodynamics book completely written in calculus? The cover looked so cool, but when I open it up, its just lines and lines and lines ...... *gets dizzy and falls asleep*
k people.. i appreciate your enthusiasm, but when i come back and see that there are replies i get somewhat happy, only to find out it is people remarking on the difficulty of the subject material etc.. doesnt help, so plz try not to spam the thread

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Sorry tintrail, I was more making the comment that you probably know more chemistry than 99.99% of the people here so you might not be able to find much help. Unless Mixed shows up. Besides, the more we talk, the higher up the thread stays and the better chance you have of someone who can actually help you seeing it.

Wuhan, yeah, I'm in my third year of aerospace, and more than halfway through! Are you talking about the Anderson book that's called "Introduction to Aerodynamics" or something like that?

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Originally Posted by AeroJonesy
Sorry tintrail, I was more making the comment that you probably know more chemistry than 99.99% of the people here so you might not be able to find much help. Unless Mixed shows up. Besides, the more we talk, the higher up the thread stays and the better chance you have of someone who can actually help you seeing it.
[COLOR=Wheat]yeah i thought of this.. thanks man.. sorry i seemed pissy.. =).. just dissapointed that noone can help, and mixed isnt around...

anywho, i emailed my prof, so i guess i should be alright...[/COLOR]

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1) Okay, here's what Google tells me, from this pdf. It seems that the maximal binding of Mg (and Zn, but that's from another article) is at a pH of 10. The Mg would probably dissociate from the EDTA at a pH lower than that, meaning that your titration would probably take longer and be less accurate. Interestingly, you use a pH of 8.0 in most biological systems involving EDTA.

2) You're missing a step, I think.
You've gone from milliequivalents/mL to just milliequivalents. You need to deal with "per mole" somewhere in there.

Edit: I disagree about dividing by 2. I think you should be multiplying, since each Ca ion can hold 2 charges. I need to examine the problem more.

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