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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: plasticfood on October 08, 2011, 03:36:56 PM

Title: What is the initial iodide concentration?
Post by: plasticfood on October 08, 2011, 03:36:56 PM

i know this seems like a simple question, but i can't figure it out.

i have a .04M of KI that's 15mL. the total solution is 100 mL. now i have to find initial iodide concentration. so i have the setup:

(100mL)(M) = (.04M KI)(15mL)

when i solve for M, would i get the concentration of KI and not iodide by itself? how do i solve for iodide exclusively?

Title: Re: What is the initial iodide concentration?
Post by: Schrödinger on October 08, 2011, 04:54:11 PM

Okay, i didn't get the question... Is it like you have 100 mL of the solution and you are separating a 15mL sample from it? If so, the concentration of the 100mL solution should be the same as that of the 15mL sample.

And if you assume KI to be completely dissociated, then the concentration of KI will be the same as that of iodide ions.

KI  :rarrow: K⁺ + I^-

Title: Re: What is the initial iodide concentration?
Post by: plasticfood on October 08, 2011, 05:28:03 PM

yeah i believe that's it. thanks.

Title: Re: What is the initial iodide concentration?
Post by: plasticfood on October 09, 2011, 03:12:31 PM

ok i don't know if i'm doing this right, but i have to find the k constant from this formula:
Rate = k [Fe3+]^a [I-]^b

i found that Fe is 0th order, and I is 2nd order, and i know what the initial rates are. for the lab, i used .04 M of KI, so do i plug that into [I-]? 

Title: Re: What is the initial iodide concentration?
Post by: Schrödinger on October 09, 2011, 04:16:55 PM

Once again, if you assume complete dissociation of KI into K+ and I-,then yes, you should plug in 0.04M

Title: Re: What is the initial iodide concentration?
Post by: plasticfood on October 09, 2011, 04:32:53 PM

ok cool thanks.