Australia's Science Forum

Hi all
I have been asked to make Fehling's for a glucose experiment for Yr.12 chemistry.I haven't been asked for this before so am wondering if it may be banned or if it is difficult to make up.
I have always given Benedict for this prac.but the teacher wants both!!!Go figure!!!
I know someone will be able to help me.
Thanks
Mother

From "The Laboratory":

Preparation:
Solution A 34.6g Copper (II) Sulfate
500ml distilled water
concentrated sulfuric acid
Dissolve the copper sulfate in the distilled water. If the solution is cloudy, add 1 or 2 drops of
concentrated sulfuric acid.

Solution B 77g sodium hydroxide
175g sodium potassium tartrate
500ml distilled water
Dissolve the sodium hydroxide and sodium potassium tartrate in the distilled water.

Fehling's Reagent
When required mix equal volumes of solutions A and B
Procedure: Mix equal volumes of Fehling's reagent and solution to be tested. Boil.

For storage, keep solutions separate.

Haven't done this personally but I have every faith in "The Laboratory"

I only know it was always used with caution because of the caustic nature of solution B. It tends to be more for indicating how much glucose is in a solution, rather than a yes/no test.

Cheers, K

Thanks
Have made the solutions up but found that the cloudy solution was B and not A as indicated in the instructions.
Many thanks
Cheers
Mother

Does any one know what goes on the labels ( Any safety warnings) for Dropper bottles.
This is the first time I have made this indicator. As it is not on the chemical labeling program.
Thanks Vicki

Hi, can you please tell us what your Ferroxyl Indicator has in it????????? This way we may be able to help you label it.

Welcome to chemtalk, Did you mean to label Ferroxyl Indicator or Fehlings Reagent, as you question was under Fehlings Reagent.

Regards Sue

Hi Vicki, If it is Potassium Hexacyanoferrate III it is now called Potassium Ferricyanide it is a red substance. It is safe for years 7-12. You should find it on chemwatch, if you are having trouble. Do get back to us.

Hi
I made these labels in Word, you can make changes, warnings are from the ChemWatch and dot according to CSIS book

Hi Pommey ...... Yes this was the first time I've asked a question. Don't know how I got to ask my question in the Fehlings reagent question.!!!
Ferroxyl Indcator is made by
* mixing up a 2% Solution of Potassium Ferricyanide ( 100ml )
* mixing up a 2% Solution of Sodium Chloride ( 100ml )
* Take 3ml of the Potassium Ferricyanide solution and add to the salt solution
* Add 2ml of Phenolphthalein solution and mix

I would presume that Toxic should be a safety warning / Green Dot
On my Labeling System Ferroxyl Indicator is not mentioned
Cheers Vicki

This should be fine, with perhpas a class 3 sticker.

Do hope it helps

Hey thanks Jazz and Sue!!!!

Cheers
Mother

Made some Ferroxyl Gel up today, 500ml Distilled water, 7.5g agar, 10ml 0.1m Phenolphthalein, 75ml of 0.1M Potassium Ferricyanide. & 5ml Sodium Chloride Saturated. All went well, used a few drops of KOH Potassium Hydroxide 2m it turns pink. Then add a few drops of HCL 0.5M and it goes back to clear or amber colour. Ok so far. I kept it on warm on a hot plate in our new fume cupboard. Ready for the students the get their nails etc ready.

It turned Green, middle green, not pale. Can any one please tell me WHY???????????????? By the way it still worked fine. It was just green

As you can see this was from Last year. I made some up only yesterday. And the same thing happened. It still worked fine, but why has it gone GREEN. Dr Rob are you out their????????????????????????????

Hi Labbie,

I can answer this quite easily for you the ferricyanide has oxidesed to ferrouscyanide changing the Iron (II) to Iron (III) (GREEN), this was probably done as the salt solution was used. There is another ingredient which makes the Potassium Ferricyanate stable it doesnt come to mind but I will find out for you and go from there. That is what your problem will be..... Simple Electrochemisty. This will work fine because don't forget all other ingredients are working correctly to achieve the desired outcome, just in a different colour.

Appologise for my absence, but Uni has finished for me for the year so i will be able to Moderate without interuption.... See you all on chemtalk...

Cheers,

Robb.....

Thank you so much Rob, Have a great break.