Testing the "freshness" of acidified Potassium Dichromate

[Ocean Breeze]

My prac calls for "freshly made " acidified potassium dichromate.
I have some soln here thats several mths old, and really would prefer to use that up if I can, and it would save me time.
Anyone know a quick freshness test for this soln?

[Labbie]

Potassium Dichromate acidified becomes Chromic Acid, which is banned in all DET schools. Best to put in the collection waste storage area to be picked up, at some time.

Sorry its a NO NO

[Ocean Breeze]

Hi Sue.

This "acidified Potassium Dichromate" is called for in one of the yr 12 pracs. Its a test reagent. We've used it every year for quite a few yrs.
I am trying to save time if I can find out if its "fresh". It has a yellow dot, and is ok for snrs to use.

[Labbie]

This is taken from Chemical Safety in schools Vol2. It explains why, in greater depth.

Due to the fact that you are producing CHROMIC ACID, by aciditying Potassium Dichromate. This acid at higher concentrations is Toxic and is known as a Carcinogenic compound, very Corrosive and very poisonous.

So banned in DET schools.

Potassium Dichromate is a Orange dot safety for 11 & 12

Regards

[fibreweb]

The recipe I have for acidified Potassium chromate calls for 1ml of 1M sulphuric acid into 20 ml of 0.02M potassium dichromate. Surely at that dilution it wouldn't create the Chromic Acid that is the nasty.

Under Potassium Dichromate (page 201 in my book) CSIS says that Chromic acid is prepared by mixing a Chromate salt with a concentrated acid. It goes on to say that if you are using acidified solution of Potassium dichromate as an oxidising agent for alcohols in organic chemistry to ensure that all solid material has disolved and the mixture is homogenouos before using.

My thought would be if it was not to be used for that purpose the manual would have said so rather then giving safety guidelines.

As to telling if it is fresh enough I would try it and if it didn't work asume it wasn't fresh enough and make up some more. The stuff I have was prepared in 2002 and I wasn't told that it didn't work when they did that prac several weeks ago.

[Ocean Breeze]

Thanks.. I just really dont have a lot of time to fiddle making unneccessary solutions!

[lada]

Not sure what you need it for, but it is an oxidizing agent, so if you want to avoid it, you could use acidified potassium permanganate.
Tell me the prac, I might be able to give you a sustitute for the future.
Lada

[Robb]

HI All,

The dilute concentration of the Sulfuric Acid will not be a problem when it comes to acidifying the Potassium Dichromate. It works very affectively.

As mentioned above by our collegues, Chromic Acid is only formed when Conc. Sulfuric Acid is combined with either Sodium Chromate, Sodium Dichromate or Potassium Dichromate. But we are all up to speed with the banned substance.

The thing to look out for is the Insoluble mass made when making Chromic Acid via the above reagents. (As this is extremely carcinogenic). "The reason why it is banned."

When it comes to determining the "freshness" of the solution, the simplest determination is to observe the colour of the solution. If the solution is not clear orange in appearance, then the solution has oxidesed into more complex Dichromatic Complexes.

This should help in your determination:

Cheers,

Robb.....

[Ocean Breeze]

We use the H+ Pot Dichr with the yr 12 Chemistry-Industrial Chemistry option.
Its an expt called "Why is Sulfuric Acid so useful?". It investigates the importance of H2SO4 as in industrial applications .

[Labbie]

Once again, well done robb. Thank you again for all that great information. What would we do with out you.

[KimFenley]

Further to Robbs comments if the colour is greenish it is old and useless.

Kim

[Ocker]

Hey Barb / Hippy
It's only good for about a week1
Just take Dropper bottles off shelf add 1 drop Sulphuric then after everyone's finished Ditch
( tech term ) and make new

[Ocean Breeze]

hey Ocker boy. Havent seen you around on the forum for a while. Thanks for the tip.

I also used your previous physics tip today. Maltese cross with induction coil. amazing how I can get it functioning with a screwdriver and wooden broom handle.

[Dee]

I know this is an old thread, but how much dilute acid do I add to a 0.1M solution of potassium dichromate to acidify it. (100mls) Is a few drops of 1M sulfuric acid enough?

I am making indicator paper for the sulfuric acid pracs in y12 Industrial chem. We didn't have success last year and I am trying again....

[Robb]

Hi All,

To re-iterate Ockers post. it is advisable to use it when there is the need for it. I wouldn't/Don't use it after at least 2 days. It is too hazardous to leave around as well.

Green solution has a larger moisture content, this means it has been oxidised to its Cr3+ state rather then the stable Cr2+. Hence why when its green the best method is disposal.

Cheers,

Robb.....

[sunray18]

I know I know ....but I really miss Chromic Acid!!! My glassware just doesn't look as clean these days....sigh....