On the 9th of November of 2018, the newly refurbished Chemistry Teaching Lab was officially opened by the Principal Colin Bailey. Prof Marina Resmini, Head of the Chemistry Department had the honour of cutting the ribbon.
First day in the labs with our 1st year students. Today we will be doing acid-base titrations to determine the amount of citric acid in a sample of a powdered fruit drink. Students will use a standard solution of NaOH as a titrating agent and Phenolphthalein as indicator.
It is September again and as usual, we start the semester with the advanced practicals in chemistry with our Master students. It seems that after the summer break our students are in a very good mood and organic synthesis under nitrogen atmosphere becomes a balloon party!!!
It is again this time of the year, the semester has been very long. One more week of practicals and we are all ready for the Christmas break!!!
This year to honour the tradition we have our ChemisTree in the teaching labs. In this post I’m unveiling the secrets behind the colours of our 2016 ChemisTree.
Blue: A pinch of Copper (II) sulfate pentahydrate in water
Red: a few drops of Ferroin indicator in water
Green: A pinch of Nickel(II) nitrate hexahydrate in water
Deep purple: A pinch of potassium Permanganate in water
Violet: Literally 1 mg of Crystal Violet per Liter of water. Crystal Violet is a very strong dye.
Pink: A few drops of Phenolphthalein in a slightly basidified solution of NaOH in water. The colour fades away after a few minutes, long enough for a nice picture.
Many thanks to Indigo and Fosca for their help and creativity.
In one of our practicals at the chemistry teaching labs of Queen Mary University of London our students are provided with a mixture of 2 unknown organic compounds that they have to separate and identify with the use of spectroscopic methods and analytical qualitative tests. One of the most common tests during the practical is the Brady’s test for the identification of aldehydes and ketones. In this test a solution of 2,4-Dinitrophenylhydrazine (2,4-DNP) is reacted with the unknown mixture and if there is an aldehyde or a ketone, a yellow to deep red precipitate is observed as a consequence of the formation of the corresponding 2,4-dinitrophenylhydrazone.
Here is a nice video from FranklyChemistry showing examples of how a positive Brady’s test looks like:
For the practical this year I realised we had run out of 2,4-DNP and we needed to buy some more. I tried to buy 2,4-DNP from usual providers such as Sigma Aldrich, Alfa Aesar and VWR among others just to find that the chemical has been discontinued because is explosive.
I thought of alternative tests like Tollen’s and Fehling’s but unfortunately they are not general for carbonyl compounds and they only work for aldehydes easy to oxidise. My next move was to consult with colleagues in the department and in the internet community. Networks like researchgate and projects like #realtimechem on twitter are incredibly useful to connect and exchange knowledge with chemists around the world.
-4-Hydrazino-7-nitro-benzofurazan has been used to make fluorescent derivatives of aliphatic aldehydes including reducing sugars.
-4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole (also known as purpald): Used for the determination of formaldehyde, gives a purple colour with aldehydes and also reacts with ketones but the product is not coloured.
-2,4-dichlorophenylhydrazine as a non-explosive alternative.
I still have to test this alternatives and if successful I hope I can write a post explaining the experience.
Ironically, I have recently found that a suitable alternative to 2,4-DNP is actually 2,4-DNP but as a solution in phosphoric acid. The 2,4-DNP solution in phosphoric acid can be purchased from Sigma Aldrich and it is advertised as an alternative to the explosive 2,4-DNP.