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Author: Subject: Gravimetric Analysis of Pyrotechnic Delay Comp
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cool.gif posted on 27-5-2021 at 11:59
Gravimetric Analysis of Pyrotechnic Delay Comp


I've been thinking for a long time on what my first actual lab write-up on here would be until a few weeks ago when I was tasked with conducting a series of gravimetric analyses written for a standard from the 1950s. I thought the topic was interesting and decided I'd share it here. There's some cool color chemistry going on that I wanted to share as well! I was looking for four particular analytes here: KClO4, BaCrO4, Nickel, and Zirconium, so this write-up will be broken up as such.

Take note that the BaCrO4 and Nickel analyses both rely on aliquots generated from the sample used in the KClO4 analysis, whereas Zirconium is conducted on fresh sample. Also feel free to snicker, roll your eyes, etc., at how dated this method is and how much more easily modern methods could give us results :D It will be an important lesson for young, professional chemists to learn now: the governments of the world are terrible at staying modern with analytical chemistry methods. I do hope some of you old heads enjoy the throwback chemistry!

Potassium Perchlorate

I didn't take many pictures here because I didn't think this part of the analysis was too interesting. I can provide some in later posts if people REALLY want them. Essentially, 1 gram of delay composition (weighed out accurately) was leached 4x with 10mL portions of boiling water through a filter. The sample + filter paper was then transferred to my oven where it dried overnight at 100C. I weighed it back and got a recovery of 94% KClO4. This part of the method was annoying to me as it seems a horribly inefficient way to get the KClO4 out of the material, and if the material was using a binder such as Ethocel or Phenolic Resin, I imagine recovery values would have been abysmal.

Nickel, Pt 1

The dried sample + filter paper from the KClO4 analysis was placed into a beaker and to it I added 40mL of 6N HCl. I boiled this for around 4 hours then allowed to sit overnight. In the morning, I vacuum filtered the contents and chucked the filter. This gave me a beautiful green filtrate:



This filtrate will be used to conduct the rest of the Nickel as well as the BaCrO4 determinations. More to follow tomorrow on the rest of the determinations (with a LOT more pictures and colors :) )

EDIT: To change photo link to hyperlink
EDIT2: I used my new imgur acct to properly embed the picture

[Edited on 27-5-2021 by ShotBored]

[Edited on 28-5-2021 by ShotBored]
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[*] posted on 27-5-2021 at 12:54


Nickel, Pt 2

I pipetted 25mL of my aliquot into a beaker and diluted to 250mL with DI water. I then added 5 grams of tartaric acid and 10 mL of 10% NH4Cl in water and stirred with a stir rod. I then checked the pH with litmus paper (definitely acidic) and added 6mL of conc. NH4OH until slightly basic with subsequent litmus paper. The solution has now become a clear, tan color



I bought this solution to a boil, then added 10mL of 1% dimethylglyoxime in EtOH while stirring. Immediately a magenta-colored precipitate formed. This precipitate is Nickel bis(dimethylglyoximate).



Next is where one of those beautiful, classic 1950s chemistry procedure steps comes into play :D:D Literally "add conc. NH4OH until the mixture has a distinct ammoniacal odor". After doing so, and noticing the odor, I have a beautiful chemistry lava lamp.



The mixture was allowed to sit on a steam bath for another 30 minutes before filtering. I poured the filtrate through, then followed with 3x 20mL washes of 50% ethanol.



Filter was dried overnight at 110C and weighed back for 98.3% recovery of Total Nickel. I scraped a bit of the Nickel bis(dimethylglyoximate) out to show




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[*] posted on 28-5-2021 at 05:54


Barium Chromate

I pipetted 100mL of the aliquot generated in Nickel, Pt 1 to a 500mL flask and diluted with DI water to 250 mL. I brought the solution to boiling, and then slowly pipetted 50mL of 3N H2SO4 into the mixture. Immediately, barium sulfate begins to precipitate out. Allowed to continue boiling gently for an hour and cool overnight.



I then filtered the barium sulfate precipitate out into a Gooch and washed first with 50 mL of 0.12N H2SO4, then 250mL of boiling water. I stuck the gooch crucible into muffler for 30 minutes and weighed back. 93.7% recovery of barium chromate. This method tends to give much lower recoveries if binder is present or if potassium perchlorate is not fully removed during the KClO4 analysis.

Zirconium

This is my favorite part of the analysis, as it involves some of the most interesting color chemistry. I start by weighing 0.5 grams of fresh sample into a flask. I then add 50 mL of conc. HCl, 25 mL of conc. HNO3, and 50 mL of conc. H2SO4.



Within a few seconds the solution turns murky brown



Within a few minutes the solution begins to turn olive green while releasing orange gas (Nitrosyl chloride?). I begin boiling the solution.



Within 30 minutes, the solution becomes more of a blue-green:



Within 45 minutes, the orange nitrosyl chloride gas is no longer present and instead white sulfur trioxide fumes appear. After seeing the white fumes, I then boil for 2 more hours, then remove the solution from heat and allow it to sit overnight. In the morning, a blue-green solution is what is left. I dilute what is left in the flask to 250 mL with DI water. White Barium Sulfate precipitate can be seen.



I filter the barium sulfate out via vacuum filtration. This leaves a cool sky-blue solution.



The beaker then goes to an ice bath to cool to 10 +/- 2C. Once the beaker reaches temperature, I add 32 mL of cold 6% Kupferron in DI water (ammonium N-nitrosophenylhydroxylamine) to the beaker. Immediately white Zirconium Oxide begins to precipitate out. I filter this out as well and wash with 100 mL of cold 1N HCl. The filter paper is put into a crucible and moved to the furnace at 350C for 15 minutes, then 900C for 30 more minutes. Weigh back yields 103% recovery of total Zirconium, I imagine the high recovery could be due to not having high quality DI water.

Anyways, I hope you all enjoy. I haven't done some good ol' fashioned acid digestions in quite some time and I thought the color chemistry was really cool, particularly the nickel bis(dimethylglyoximate) complex. I know from my undergrad research that nickel can have some really cool color complexes, but I never really saw many that gave such a vibrant red.

Offhand, I am not 100% sure what is causing the light blue coloration of the solution we see during the zirconium analysis. I do remember that nickel tetrahedral complexes tend to be bright blue...any answers there would be appreciated!
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