Sciencemadness Discussion Board - Starch-Iodide Test Papers

Starch-Iodide Test Papers

aga - 28-8-2016 at 07:51

One of the remaining items needed to follow magpie's Congo Red synth is some starch-iodide test paper.

Apparently it is a good test for strong oxidisers, such as H₂O₂, Cl₂ etc.

Incredibly simple to make from starch, KI and some filter paper :
https://www.youtube.com/watch?v=ztXFWo0DyWk

Add about 150ml water to a beaker, 1g starch, 1 spatula of KI, heat up with stirring, dunk in some filter paper, hang it up to dry, then cut into strips. Done !

Works too. Slightly damp, this strip instantly changed colour when exposed to the slightest whiff of chlorine :

Velzee - 28-8-2016 at 10:42

(Yay! One of my favorite dudes is back!!)

Yep! I've heard of this before, but I don't think I've seen it done. Thank you, aga, for the video and post!

aga - 28-8-2016 at 11:12

Thanks for the thanks !

It is always good to know how to make all the stuff you need, so this seemed like a good (and easy) thing to make.

Basically ScienceMadness is the Best chemistry forum ever.

It's also very much like a drug : once hooked, there is no way out.

Whilst wandering in the Wilderness for the past few weeks, i encountered a few other SM exiles.

Likely some will return one day, hopefully soon.

Magpie - 29-8-2016 at 08:17

You can also make lead acetate paper for the detection of H2S.

aga - 29-8-2016 at 08:25

Wha !

I think my nose will pick it up sooner !

aga - 3-9-2016 at 12:21

Normal Saturday afternoon, neutralising some conc sulphuric acid that is laden with dissolved Cl₂ as usual, and the gas pours out of the beaker, so i thought i'd try out those test papers versus universal pH papers.

The home-made one at least shows something (clearly unevenly coated) and amazingly the gas just bleaches the bejeesus out of the pH paper !

A shiny new nut-n-bolt was put in a beaker and had a little gas poured over it, then was left covered for 20 mins.

Definitely not nice stuff that chlorine !

NEMO-Chemistry - 4-9-2016 at 01:37

No thread would be complete without a stupid question, so i feel its my duty to ask it.

I take it starch is starch? What i mean is you can get corn starch, tapioca starch, potato starch and so on. So does it matter what starch?

I think making them is a much better idea, saves buying in booklets that degrade in the back of the cupboard.

As for chlorine, it makes you wonder what that last sniff you had did to the lungs! I think generally the population as a whole dont think chlorine thats bad, we are so used to it in bleach and swimming pools etc.

I dont think too many people (general population not people messing with chemicals) take chlorine that seriously, shocking when you see what it can do.

Cool experiment BTW, i have some KI so i will give this a go.

j_sum1 - 4-9-2016 at 02:45

Chlorine is colloquial for any chemical containing chlorine atoms. I have come across many people who think that chlorine is a solid white substance -- after all, pool chlorine is a white powder.

So we (again) get a chemical term that has entered common parlance with people having no idea of its properties.

aga - 4-9-2016 at 03:49

I used potato starch.

https://www.youtube.com/watch?v=PgKR6EsKl5I

Metacelsus - 4-9-2016 at 05:35

Anything with amylose will work, so corn, potato, and tapioca starch will all be good.

NEMO-Chemistry - 4-9-2016 at 07:19

At last i have something i can do with 2kg of tapioca starch!

You have me thinking what other test strips can be made at home?

I really like the idea of these ones.

Aga you sure thats sulphuric acid with chlorine? Looks alot like recycled beer in a cup TBH

aga - 4-9-2016 at 11:28

100% certain.

I've made Both and know that recycled beer is a <b>much</b> lighter yellow, and tends not to smell of chlorine, depending on where you take a pee.

NEMO-Chemistry - 4-9-2016 at 16:24

I tried this today and failed (kind of). Would bleached paper make a difference? I soaked mine and before it had dried properly it had gone dark.

I used tapioca starch and cheapo filter paper, i also tried some on acid free butchers paper, its too thin to use but it didnt change colour.

So i am wondering if maybe the filter paper is bleached?? Then again surely if it affects this then its not going to any good for filtering anything.

Maybe i just fucked it up, i will give it another go tomorrow.

S.C. Wack - 5-9-2016 at 15:21

What filter paper isn't bleached, maybe some coffee filter...unbleached paper will not help one see the iodine complex...doubled-up coffee filters will work and so will Chinese filter paper even, when prepared according to the directions of Norris...using corn starch and at least nearly approx. around 50 mgs KI: Grind about 1 g of starch with a few ml of water and pour the mixture into 200 ml of boiling water. Cool the solution and dissolve in it a crystal of potassium iodide. Insert pieces of filter-paper into the solution, and hang them up to dry in a place free from acid vapors.

aga - 12-9-2016 at 13:13

Yep S.C. , that's the secret formula.

I skipped the cooling part, reasoning that they'd dry quicker.

I just used some of the round filter papers i have, undoubtedly bleached.

Magpie - 12-9-2016 at 14:19

I think any kind of paper will work, obviously white will be better for seeing the color change to blue/purple. Cooking the starch is the secret IMO.

aga - 12-9-2016 at 14:44

Please explain.

All i got left is to make benzene in order to copy your Congo Red synth from napthalene mothballs, which are nowhere near as easy to acquire (here) as Klein found, wherever he was.

If my Starch papers are crap, Please state Why, and how they should be prepared, as following your synth is not uncomplicated.

It would be a real PITA if it all went tits up at the last step.

Edit:

Lab ambient has now reduced to 34 C, so Summer (48+ C) has passed.

In a week or two i can stop venting the acetone/ethanol/HNO₃/etc bottles and maybe Do some actual chemsitry again.

[Edited on 12-9-2016 by aga]

Magpie - 12-9-2016 at 15:33

Quote: Originally posted by aga

Please explain.

All i got left is to make benzene in order to copy your Congo Red synth from napthalene mothballs....

Do you mean benzidine?

Quote: Originally posted by aga

If my Starch papers are crap, Please state Why, and how they should be prepared, as following your synth is not uncomplicated.

I make my starch papers for iodine testing using the procedure in Brewster, p.124 (forum library). I cut up strips of lab grade filter paper and soak them in the solution, then air dry.

Quote: Originally posted by aga

It would be a real PITA if it all went tits up at the last step.

yes!

NEMO-Chemistry - 12-9-2016 at 16:34

Quote: Originally posted by aga

Please explain.

All i got left is to make benzene in order to copy your Congo Red synth from napthalene mothballs, which are nowhere near as easy to acquire (here) as Klein found, wherever he was.

If my Starch papers are crap, Please state Why, and how they should be prepared, as following your synth is not uncomplicated.

It would be a real PITA if it all went tits up at the last step.

Edit:

Lab ambient has now reduced to 34 C, so Summer (48+ C) has passed.

In a week or two i can stop venting the acetone/ethanol/HNO₃/etc bottles and maybe Do some actual chemsitry again.

[Edited on 12-9-2016 by aga]

Got the other problem here! normal temp in garage ~7C, so everything needs heating lol

Magpie - 12-9-2016 at 17:09

Quote: Originally posted by aga

If my Starch papers are crap, Please state Why, and how they should be prepared, as following your synth is not uncomplicated.

What we may have here is "a failure to communicate." I never said your starch papers are crap: the picture you show looks good to me.

Edit: I recommend that you test your paper on a nitrite solution. That's what you need it for.

[Edited on 13-9-2016 by Magpie]

aga - 13-9-2016 at 00:42

Sorry, text is such a narrow bandwidth media.

All i meant to convey was concern that i'd missed something, and that my Congo Red attempt would go all fubar (right at the end) due to a botched bit of test paper.

Thanks - i'll try out the papers with some nitrite solution.

aga - 15-9-2016 at 12:33

Well, glad i tested the papers with the sodium nitrite as suggested.

They react rapidly to NO_x and 3% H₂O₂ yet not to a solution of what i imagined was sodium nitrite.

The papers are fine, but the nitrite is shitrite.

I guess i chickened out too quick when the lead/sodium nitrate reaction went all vesuvius.

Magpie - 15-9-2016 at 18:43

Before you throw out your nitrite make a dilute aqueous solution, then add a few drops of HCl or H2SO4, then test it with your starch-iodide paper. I just did this: no color change until the HCl was added, then an intense blue. My paper was made in 2007.

You should also see a lot of bubbles formed when the HCl is added. This would be NO which I think is the actual oxidant.

6NO2- + 4H+ ---> 4NO(g) + 2H2O + 2NO3-

aga - 16-9-2016 at 00:47

Life saver ! Thanks.

The nitrite certainly makes loads of NO_x when HCl is added, and the papers react instantly to that.

Wasn't looking forward to re-doing the molten lead thing again.

Magpie - 16-9-2016 at 09:55

You're welcome aga. I also did another interesting test for nitrite:

Prepare a small ice bath using, say, a 250mL beaker. Add a gram or so of table salt on top of the ice to get things really cold. Fill a small test tube half full of DI water and place a 1/4" chunk of your nitrite in it and dissolve. Place the test tube in the ice bath and wait until the solution is cooled. Then add 5-10 drops of HCl or H2SO4. You should see the beautiful blue color of nitrous acid, HNO2.

NO2- + H+ --> HNO2 (unstable)

I'm using lab grade NaNO2 so your results may vary, depending on the quality of your nitrite salt.

Sulaiman - 16-9-2016 at 13:58

I noticed on the nitrite Wikipedia page

"Sodium nitrite is made industrially by passing "nitrous fumes" into aqueous sodium hydroxide or sodium carbonate solution"

so next time I need to get rid of NOx fumes i know what to do

aga - 17-9-2016 at 08:28

Hmm. Tried cold NaNO₂ solution with both HCl and H₂SO₄ and just got some more brown gas.

There *may* have been a faint 1mm deep ring of blue floating on top of the liquid for a second, but that could have been a trick of the light.

aga - 26-11-2016 at 02:44

After all the messing about, i discovered today that i simply did not know how to use starch-iodide papers properly.

Turns out that they need to be wetted with a 1% HCl solution first.

http://chestofbooks.com/science/chemistry/Processes-Dye-Chem...

Doing that with one of the remaining papers (wasted most of them) it went dark blue with 1 drop of a very dilute NaNO₂ solution.

The nitrite and the papers were both actually OK from the beginning !

Edit:

If i'd understood what Magpie said earlier, i'd have known sooner.

[Edited on 26-11-2016 by aga]

S.C. Wack - 26-11-2016 at 06:30

In the usual usage the solution to be tested is already acidic and may even need to be diluted with water before dropping it on the paper.

aga - 26-11-2016 at 11:06

Quote: Originally posted by S.C. Wack

In the usual usage the solution to be tested is already acidic

Thank you for that info.

So obvious now i think about it, yet i've been hung up on this for months !

In retrospect, i think i went wrong by thinking of an 'indicator' as something magical, and not just another a chemical reaction.

Sodium Iodide?

Acuyo - 6-3-2017 at 20:19

Can this preparation be done with naoh instead of koh, or is potassium necessary?