Just a technical question
I need to make up 500ml of 0.0125M Iodine,I solution. I've been told I need to disolve the iodine in Potassium Iodide, but I don't know the strength of the KI solution I need. Can anyone tell me how to work that out?
Making Iodine
-
rae
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Making Iodine
The word according to " The Laboratory"page 75 says:
0.1M Iodine Solution (Iodine in Potassium Iodide)( I'm sure you can do the maths to make the molarity you require)
12.7g Iodine
16.6g Potassium Iodide
1Litre Water
Dissolve potassium iodide in n600ml distilled water
Add iodine and allow to dissolve
Make up to 1Litre
Note: Make 24 hours before required as iodine is slow to dissolve
Store in a tightly closed nbrown glass bottle. iodine solutions deteriorate with light and age.
Hope this helps.
Lorrae
0.1M Iodine Solution (Iodine in Potassium Iodide)( I'm sure you can do the maths to make the molarity you require)
12.7g Iodine
16.6g Potassium Iodide
1Litre Water
Dissolve potassium iodide in n600ml distilled water
Add iodine and allow to dissolve
Make up to 1Litre
Note: Make 24 hours before required as iodine is slow to dissolve
Store in a tightly closed nbrown glass bottle. iodine solutions deteriorate with light and age.
Hope this helps.
Lorrae
Calculating 0.0125M Iodine Solution.
Hi Justin,
Just to let you know that the above preparation step for Iodine is perfect for the 0.1M solution. If you are specifically looking at an accurate solution of 0.0125M Iodine, Potassium Iodide with Iodine cannot be used. The Potassium Iodide contains iodine with potassium. Meaning that you have to compensate via compensating for Potassium in the calculation, hence the the final concentration will be considerably inaccurate.
To prepare Iodine solution the solvent you will be using is Ethanol with a little water to reduce the amount of Ethanol evaporation to a minimum.
Using the two formula’s
No of moles = mass/Formula Weight
AND
Molarity = no of moles/Volume (expressed in litres)
Therefore we can work from there:
Iodine Atomic Mass = 253.81 (I[sub]2[/sub])
Therefore
Number of moles = Molarity X Volume (L)
= 0.0125 X 0.500 (the 500mL must be expressed in litres)
= 0.00625
Therefore:
number of moles = mass/ Formula weight
Mass = 0.00625 X 126.904 (divide 253.81 by 2 due to I[sub]2[/sub])
= 0.79315
= 0.79315g
Therefore: you will weigh 0.793g of Iodine in a 500mL volumetric Flask and dissolve this in 400mL of Ethanol and approx 100mL of Water. ( I say Approximately 100mL of water because it will take a little more, as the water molecules are smaller compared to Ethanol molecules).
Dissolve the iodine crystals in the Ethanol first then finally add the water, this allows for dissolution to occur more efficiently.
I hope this has been informative for you.
Robb….
Just to let you know that the above preparation step for Iodine is perfect for the 0.1M solution. If you are specifically looking at an accurate solution of 0.0125M Iodine, Potassium Iodide with Iodine cannot be used. The Potassium Iodide contains iodine with potassium. Meaning that you have to compensate via compensating for Potassium in the calculation, hence the the final concentration will be considerably inaccurate.
To prepare Iodine solution the solvent you will be using is Ethanol with a little water to reduce the amount of Ethanol evaporation to a minimum.
Using the two formula’s
No of moles = mass/Formula Weight
AND
Molarity = no of moles/Volume (expressed in litres)
Therefore we can work from there:
Iodine Atomic Mass = 253.81 (I[sub]2[/sub])
Therefore
Number of moles = Molarity X Volume (L)
= 0.0125 X 0.500 (the 500mL must be expressed in litres)
= 0.00625
Therefore:
number of moles = mass/ Formula weight
Mass = 0.00625 X 126.904 (divide 253.81 by 2 due to I[sub]2[/sub])
= 0.79315
= 0.79315g
Therefore: you will weigh 0.793g of Iodine in a 500mL volumetric Flask and dissolve this in 400mL of Ethanol and approx 100mL of Water. ( I say Approximately 100mL of water because it will take a little more, as the water molecules are smaller compared to Ethanol molecules).
Dissolve the iodine crystals in the Ethanol first then finally add the water, this allows for dissolution to occur more efficiently.
I hope this has been informative for you.
Robb….
Last edited by Robb on 21 Aug 2006, 15:42, edited 1 time in total.
Dr Robert Crosdale. MRACI. NSS. NSSA. NASA.
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The conventional way of making iodine solution is to use potassium iodide to dissolve iodine as described by Lorrae. It forms KI3, permitting far greater concentrations of iodine to be solubilised. The KI3 is readily dissociated releasing the iodine. The iodide ion does not affect the available iodine concentration in the sense suggested by Robb.
Wombat
Wombat
Making of Iodine
When the Tri-Iodide molecule is identified within specific reactions whether in dissolution or specific reactions one must not forget that the Central Iodine Atom shares 5 Lone Pairs of electrons. This means that the set of 5 pairs requires a tri-agonal bi-pyramid arrangement, which in turn requires a set of dsp3 orbitals.
The outer iodine atoms have four pairs of electrons, which calls for a tetrahedral arrangement and sp3 hybridisation.
What I am trying to say is that since the inner iodine atom within the tri-iodide structure requires the fifth pair of electrons to separate from the outer two sharing iodine atoms, and it is with this that the iodine availability is somewhat reduced due to this factor of what we call hybridisation.
Having said that, this occurs very slowly and this is what causes the added Iodine to dissolve slowly. Usually within the 24 hour period.
But due to this process being quite slow, I intend to make up Iodine Solutions via direct dissolution within the alcoholic environment. By all means there is no pun intended, but to make minute concentrations by all means this works well otherwise Hybridisation will cause nothing to dissolve.
Don't get me wrong, the above methods are fine and are perfect for mid to high range concentrated solutions.
Thanks for bringing this to my attention Wombat.
I hope this has not added to any confusion..
Robb.....
The outer iodine atoms have four pairs of electrons, which calls for a tetrahedral arrangement and sp3 hybridisation.
What I am trying to say is that since the inner iodine atom within the tri-iodide structure requires the fifth pair of electrons to separate from the outer two sharing iodine atoms, and it is with this that the iodine availability is somewhat reduced due to this factor of what we call hybridisation.
Having said that, this occurs very slowly and this is what causes the added Iodine to dissolve slowly. Usually within the 24 hour period.
But due to this process being quite slow, I intend to make up Iodine Solutions via direct dissolution within the alcoholic environment. By all means there is no pun intended, but to make minute concentrations by all means this works well otherwise Hybridisation will cause nothing to dissolve.
Don't get me wrong, the above methods are fine and are perfect for mid to high range concentrated solutions.
Thanks for bringing this to my attention Wombat.
I hope this has not added to any confusion..
Robb.....
Dr Robert Crosdale. MRACI. NSS. NSSA. NASA.
Ph.D (Chem), Post Grad Ph.D (Physics), M.Ed, B.Sc (Hons), Dip. Appl. Sc. (Chem)
Lake Munmorah High School.
University of New England.
University of New South Wales.
University of Newcastle.
To understand the Universe from our perspective, we need to look towards our own backyard first for answers.
** AD ASTRA PER ASPERA - SEMPER EXPLORO **
Ph.D (Chem), Post Grad Ph.D (Physics), M.Ed, B.Sc (Hons), Dip. Appl. Sc. (Chem)
Lake Munmorah High School.
University of New England.
University of New South Wales.
University of Newcastle.
To understand the Universe from our perspective, we need to look towards our own backyard first for answers.
** AD ASTRA PER ASPERA - SEMPER EXPLORO **
Hi Justin,
My Iodine solution is as follows:
3g iodine
15g potassium iodide
1 litre distilled water
Dissolve potassium iodide in approx. 800ml of the distilled water and then add the iodine. Make up to 1 litre with distilled water.
NOTE Make 24 hours before required, as iodine is slow to dissolve.
Hope this helps
Kath
My Iodine solution is as follows:
3g iodine
15g potassium iodide
1 litre distilled water
Dissolve potassium iodide in approx. 800ml of the distilled water and then add the iodine. Make up to 1 litre with distilled water.
NOTE Make 24 hours before required, as iodine is slow to dissolve.
Hope this helps
Kath
Rob quoted above
"But due to this process being quite slow, I intend to make up Iodine Solutions via direct dissolution within the alcoholic environment. To make minute concentrations by all means this works well otherwise Hybridisation will cause nothing to dissolve.
Don't get me wrong, the above methods are fine and are perfect for mid to high range concentrated solutions."
Not quite following you in this area Rob can you elaborated more please.
"But due to this process being quite slow, I intend to make up Iodine Solutions via direct dissolution within the alcoholic environment. To make minute concentrations by all means this works well otherwise Hybridisation will cause nothing to dissolve.
Don't get me wrong, the above methods are fine and are perfect for mid to high range concentrated solutions."
Not quite following you in this area Rob can you elaborated more please.
Making of Iodine
Hi Kevin,
What I mean by making the Iodine solution up, is that I use pure Iodine and add this to 95% Ethanol. For your information: Some bottles of Ethanol quote 98% but Pure Ethanol is Hydroscopic, where it absorbs some water from the atmosphere. So if the bottle says 98% it really is 95%.
Hope this helps in the explanation.
Cheers,
Robb.....
What I mean by making the Iodine solution up, is that I use pure Iodine and add this to 95% Ethanol. For your information: Some bottles of Ethanol quote 98% but Pure Ethanol is Hydroscopic, where it absorbs some water from the atmosphere. So if the bottle says 98% it really is 95%.
Hope this helps in the explanation.
Cheers,
Robb.....
Dr Robert Crosdale. MRACI. NSS. NSSA. NASA.
Ph.D (Chem), Post Grad Ph.D (Physics), M.Ed, B.Sc (Hons), Dip. Appl. Sc. (Chem)
Lake Munmorah High School.
University of New England.
University of New South Wales.
University of Newcastle.
To understand the Universe from our perspective, we need to look towards our own backyard first for answers.
** AD ASTRA PER ASPERA - SEMPER EXPLORO **
Ph.D (Chem), Post Grad Ph.D (Physics), M.Ed, B.Sc (Hons), Dip. Appl. Sc. (Chem)
Lake Munmorah High School.
University of New England.
University of New South Wales.
University of Newcastle.
To understand the Universe from our perspective, we need to look towards our own backyard first for answers.
** AD ASTRA PER ASPERA - SEMPER EXPLORO **
Re: Making Iodine
Hi Rob,
I used iodine crystals and they dissolved fine, though it was running out so we ordered some more this type didn't dissolve very well , it was tiny beads (not crystals) so for the remainder I finished off the iodine crystals. Do you have any pointers Rob as to why it didn't dissolve in the ethanol??
thanks
I used iodine crystals and they dissolved fine, though it was running out so we ordered some more this type didn't dissolve very well , it was tiny beads (not crystals) so for the remainder I finished off the iodine crystals. Do you have any pointers Rob as to why it didn't dissolve in the ethanol??
thanks
Making Iodine
Hi Kevin,
The manufacturing process of this type of Iodine (pellets or Beads) have just compacted the Crystal to an almost perfect round shape. This is to aid in the Iodine to not stick upon storage.
It is this compaction that makes the Iodine harder to dissolve, than the crystalline type.
If you have a magnetic stirrer, this would help and also heating the Ethanol up a little would also speed the dissolution up as well.
If you were to heat the Ethanol up, use just over half of the volume needed to have warmed and use this to dissolve the Iodine and allow to cool. Then simply add the rest of the volume to make up the final volume of interest. This will certainly help in your problem.
Cheers,
Robb.....
The manufacturing process of this type of Iodine (pellets or Beads) have just compacted the Crystal to an almost perfect round shape. This is to aid in the Iodine to not stick upon storage.
It is this compaction that makes the Iodine harder to dissolve, than the crystalline type.
If you have a magnetic stirrer, this would help and also heating the Ethanol up a little would also speed the dissolution up as well.
If you were to heat the Ethanol up, use just over half of the volume needed to have warmed and use this to dissolve the Iodine and allow to cool. Then simply add the rest of the volume to make up the final volume of interest. This will certainly help in your problem.
Cheers,
Robb.....
Dr Robert Crosdale. MRACI. NSS. NSSA. NASA.
Ph.D (Chem), Post Grad Ph.D (Physics), M.Ed, B.Sc (Hons), Dip. Appl. Sc. (Chem)
Lake Munmorah High School.
University of New England.
University of New South Wales.
University of Newcastle.
To understand the Universe from our perspective, we need to look towards our own backyard first for answers.
** AD ASTRA PER ASPERA - SEMPER EXPLORO **
Ph.D (Chem), Post Grad Ph.D (Physics), M.Ed, B.Sc (Hons), Dip. Appl. Sc. (Chem)
Lake Munmorah High School.
University of New England.
University of New South Wales.
University of Newcastle.
To understand the Universe from our perspective, we need to look towards our own backyard first for answers.
** AD ASTRA PER ASPERA - SEMPER EXPLORO **
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Ian
- Posts: 575
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- School: Macarthur Anglican School
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Re: Making Iodine
Wow! I have just got back after a couple of weeks off, and this is the first thread that I have looked at! I think I might have to go and find an "alcoholic environment". 
I often just throw "a bit" of KI in a beaker, and throw in "a bit" of I and top it up with water. If it is not dark enough, I throw in some more!. The teachers seem happy. I never knew it was so complicated.
regards
Ian
I often just throw "a bit" of KI in a beaker, and throw in "a bit" of I and top it up with water. If it is not dark enough, I throw in some more!. The teachers seem happy. I never knew it was so complicated.
regards
Ian
Re: Making Iodine
Hi everyone,
I also have to confess I usually just chuck in some I into some metho and if it is dark enough everyone is happy. It indicates the presence of starch which is the common reason for using i
Cheers,
Robbie
I also have to confess I usually just chuck in some I into some metho and if it is dark enough everyone is happy. It indicates the presence of starch which is the common reason for using i
Cheers,
Robbie
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kimmy
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Re: Making Iodine
Well some of us are as they say "bucket Chemistry" lovers yep I just add a few crystals into some Ethonal and add more if it is not very dark. Seems to work and no one around here has complained yet. And it shows up the presence of starch - so I suppose that is the main thing.
