Description
Calcium arsenide has the molecular formula of
Ca3As2 and the molecular weight of 270.0772 g/mol. It may be prepared by reacting the elements together.
Since As sublimes at 614°C and Ca melts at 839°C,
the latter is melted at about 875°C in an inert atmosphere
like argon (not N2 which would form nitrides)
and arsenic vapors are carried into the reaction zone
by a stream of Ar gas:
3Ca + 2As + heat Ca3As2
Its CAS number is 12255-53-7. The standard Gibbs
energies of formation of Ca3As2 was determined by
a chemical equilibration technique yielding the
following results:
3Ca + 2As Ca3As2 (solid)
△G°= -723,800 + 172.8T (J/mol)
(T = 1273 to 1573 K)
Calcium arsenide has the zinc-blende (cubic) structure
with a = 6.751 . It can also be prepared by the
reduction of calcium arsenate by carbon:
2Ca3AsO4 + 5C + heat Ca3As2 + 2CaO + 3CO2
