<<< Return to Spanish versionGermans Max von Laue and James Frank received the Nobel Prize in Physics in 1914 and 1925, respectively. The first was a clear opponent of the Nazi regime and the second was Jew. When World War II began, these two physicists sent their commemorative medals awards to Niels Bohr’s Laboratory (Nobel Prize in Physics in 1922), in Copenhagen, so that he had a safe place until the end of the war. But medals are gold and gold export from Germany was a very serious offense at that time. Regrettably, Denmark was invaded and as the Bohr’s lab had become a refuge for Jewish physicists and would received a Nazi visit, so he had to hide medals but the name of the winner was recorded in them.
To avoid the
capture and the likely punishment to these researchers, the Hungarian George de
Hevesy (Nobel Prize in Chemistry in 1943) chose the chemistry way “to
hide" the medals. But gold, being a noble metal, does react with almost
nothing, adding more difficulty to the problem. Finally, de Hevesy chose to
dissolve the medals in aqua regia, a solution discovered in the ninth century
AD, composed of nitric acid (HNO3) and hydrochloric acid (HCl) in a rate
1:3.
The power to
dissolve of aqua regia comes from the combined properties of each acid. In the
first step, HNO3 acts as oxidizer and leads gold from the oxidation state 0 to
+3.
Au (s) + 3 NO3- (aq) + 6
H+ (aq) → Au3+ (aq) + 3 NO2 (g)
+ 3 H2O (l)
The chloride ions in the HCl react with Au3+ ions, generating complexed auric tetrachloride ions, stable and soluble compounds.
Au3+ (aq) + 4 Cl- (aq) → AuCl4- (aq)
The resulting
orange solution was poured into a dark bottle and gold of medals was unnoticed
for years in Bohr's laboratory.
When finished
World War II, de Hevesy decided to recover the dissolved gold by precipitating,
ie, returning back to its solid state. For that, he used sulfide dioxide from
sodium sulphite as a powerful reducing (Na2SO3 + 2H+
→ 2 Na+ + SO2 + H2O).
2 AuCl4-
(aq) + 3 SO2 + 6 H2O → 2 Au (s) + 3 SO42- + 8 Cl- + 12 H+
Finally, gold
was sent to the Swedish Academy, which produced new medals that were returned
to their rightful owners in 1950, on the 50th anniversary of the Nobel Prizes.
By @JGilMunoz
<<< Return to Spanish version
This post comes from my question proposed for scientific quiz “GoldenSquirrel” and also participates in the XLIX Spanish Carnival of Chemistry.
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