Sciencemadness Discussion Board

Wrong dichromate received!

Lion850 - 6-12-2019 at 01:43

Around the start of November I placed 2 orders for chemicals with a supplier. The first order included potassium dichromate, and the second order included both sodium and ammonium dichromates.

Yesterday my daughter wanted to see the 'volcano' demo for which ammonium dichromate is used. But I could not get the red powder received in a plastic jar with label "ammonium dichromate" to decompose when heated - instead it melted into an orange liquid that turned slightly black with strong heating and then solidified back into an orange solid. I immediately suspected that when was send is not ammonium dichromate. I compared the 3 dichromates I received but they more or less look the same. I then also heated up small amounts of the potassium and sodium dichromates in test tubes and they also melted and then solidified again, apparently without any chemical change. As is correct for potassium and sodium dichromates.
I contacted the supplier who did not seem all that surprised! Istead they asked if I found issues with any of the other 8 or so chemicals that were in the same order. They promised to investigate and ring back.
I was quite sure the "ammonium" dichromate was in fact also either potassium or sodium but which one? Flame color tests was not really conclusive so I decided to check the solubility in water.
I added 20ml water in a small beaker and dissolved the dichromate labelled as potassium 1gram at a time. 2g dissolved easily, the 3rd slower, and the 4th did not all dissolve. To me this was correct for potassium dichromate (ambient temp was around 30 deg C).
I then did the same with the sodium dichromate and stopped when I got to 12g (into 20ml water) and it still dissolved easily. This told me it was most likely sodium dichromate (much more soluble than the potassium).
I then did the same for the "ammonium" dichromate. It behaved the same as the potassium: 3g dissolved but not the 4th gram.
So at this stage I assume the "ammonium" dichromate is in fact potassium dichromate. Needless to say this is not good at all. In this case no harm resulted in the supplier supplying the wrong chemical but potentially such an error can have serious consequences.
I have not used any of the other chems I got from them yet but I will for sure be on the lookout for anything unexpected when I do.
I plan to get rid of the incorrectly labelled dichromate; must look for a way to convert it into a chromium salt.

B(a)P - 6-12-2019 at 03:22

Which supplier?

Ubya - 6-12-2019 at 03:43

always check your chemicals when they arrive, as you said a mistake could be dangerous. at least it was a dichromate, easy to identify, imagine ordering a chemical in the form of a white powder, but it is the wrong one, good luck figure it out. if your doughter didn't ask you for the demonstration, you could have had that labeled incorrectly for months or years, and once you would eventually find it out, the seller might not help you anymore

fusso - 6-12-2019 at 04:17

I remember there's at least 1 thread about receiving wrong chems. Should this be merged?

Boffis - 7-12-2019 at 04:32

@Lion850 sodium dichromate is a little more soluble than the potassium salt and is generally the dihydrate so when you heat sodium dichromate in a test tube, before it melts water condensation occurs high up in the test tube. If you have perchloric acid or sodium perchlorate, adding a strong solution to a solution of potassium dichromate will give a copious crystalline ppt of potassium perchlorate, it would normally be white but I suspect that some occluded dichromate will stain the ppt orange.

Lion850 - 8-12-2019 at 22:53

Quote: Originally posted by B(a)P  
Which supplier?


It was supplied by Vanbar. They called me today and told me they did some tests and they are now also suspicious about the "ammonium" dichromate they have and have pulled the stock in the meantime. And refunded my purchase cost.

j_sum1 - 8-12-2019 at 23:22

Quote: Originally posted by Lion850  
Quote: Originally posted by B(a)P  
Which supplier?


It was supplied by Vanbar. They called me today and told me they did some tests and they are now also suspicious about the "ammonium" dichromate they have and have pulled the stock in the meantime. And refunded my purchase cost.

Ok. I now know where I am getting my next round of potassium permanganate from. As well as sodium thiocyanate and... lots of other things.

Thanks for this. I did not know this supplier existed.
https://www.vanbar.com.au/catalogue/index.php?item1=CHEMISTR...