I've read that group 1 elements and group 2 elements with exception of Be form blue-colored solutions in liquid ammonia (Mg requires an electrolytic process). What are the conditions for a metal to form a solution in liquid ammonia, and which metals (other than what I have mentioned) form blue-colored solution in liquid ammonia? Can aluminium also form such solution?
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1$\begingroup$ Blue is the color of the solvated electron. Only the most active metals do that. $\endgroup$– Ivan NeretinCommented Aug 15, 2020 at 8:55
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$\begingroup$ Can Aluminium do that? $\endgroup$– AdithyaCommented Aug 15, 2020 at 8:58
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$\begingroup$ I'd say it is unlikely, but I don't know for sure. $\endgroup$– Ivan NeretinCommented Aug 15, 2020 at 9:00
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1$\begingroup$ The textbook blue solvated e- is already difficult to achieve with alkali metals... The answer might practically be yes or no. Written after seeing that is possible according to an answer below and its citation. $\endgroup$– AlchimistaCommented Aug 15, 2020 at 21:58
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1$\begingroup$ Consistency between question and accepted answer: If we are allowing an electrolytic process for aluminum, then one should be allowed for magnesium and that works too. Question edited accordingly. $\endgroup$– Oscar LanziCommented Aug 16, 2020 at 14:46
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2 Answers
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The SE answers quoted in the comments provide a good broad answer but with respect to the question of aluminium – aluminium will form a blue solution in liquid ammonia following electrolytic reduction of $\ce{AlI3}$ in liquid ammonia according to J. Am. Chem. Soc. 1950, 72 (11), 5178–5180.
Europium and ytterbium have also been reported to dissolve in liquid ammonia in J. Phys. Chem. 1956, 60 (11), 1590–1591.
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Yes, aluminium forms a blue colored solution in liquid ammonia. Liquid ammonia will dissolve group 1 (alkali) metals and other electropositive metals such as calcium, strontium, barium, magnesium, aluminum, europium, and ytterbium. At low concentrations (ca. $\pu{0.06 mol/L}$), deep blue solutions are formed: these contain metal cations and solvated electrons. The solvated electrons are stable in liquid ammonia and form a complex: $\ce{[e^-(NH3)6]}$. For further details see Chemistry of the main group elements by Andrew R. Barron on openstax cnx.org.