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### Topic: DEtermine Iodide content of salt by standard addition  (Read 5192 times)

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#### Crazy_girl

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##### DEtermine Iodide content of salt by standard addition
« on: April 14, 2011, 09:43:10 AM »
How would you determine the iodide content of table salt from this data.

the mass of table salt weighed was 1.567 grams this was placed in a 25 ml volumetric flask and diluted with water. This was then placed in a beaker and the potential was measured using electrodes.

a standard solution containing 0.1972 grams of NaI and 3.007 g of NaCl (made up in a 1000ml flask). I worked out the concentration for this and it was 1.63 x 10-3M. Since this molarity was 5 times the concentration we really wanted.  10 ml of this solution was added to a 50 ml flask and diluted to the mark with water. Using C1V1=C2V2 i got that the concentration in the 10mL was 2.63 x10-4M. 1mL aliquots of this solution was added to the solution in the beaker and the potential was taken. This was repeated until 6 ml in total were added.

What i dont know is what graph to plot would it be a emf vs {I-} and how would you determine the [I-] concetrations.

The results were:
0mL -0.6mV
1mL -28.3mV
2 ml -42.0mV
3mL -58.3mV
4ml -65.4mv
5ml - 72mv
6ml - 75mV
I just want to know the basics

#### Borek

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##### Re: DEtermine Iodide content of salt by standard addition
« Reply #1 on: April 14, 2011, 10:25:17 AM »
Nerns't equation.
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#### Christas28

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##### Re: DEtermine Iodide content of salt by standard addition
« Reply #2 on: March 15, 2012, 06:40:09 PM »
I've been doing a similar lab this week, and although this topic is long past I still think it will be useful to post this link.
http://www.chem.uic.edu/fetzer/chem222/Exp_K51.pdf
This explains what you equation you should use to determine the  I- ion concentration.

Also if you have "Quantitative Chemical Analysis" by Daniel Harris, you can see chapter 15 on Electrodes and Potentiometry.
The equation for a standard addition plot for the ion-selective electrode:
(V0 + VS)10E/S= 10k/S V0 cx + 10k/S VS cS

where the equation follows: y= b +m. x

when y= 0
x-intercept= -b/m ==> = -10k/S V0 cx/ 10k/S cS
= -V0 cx/ cS