Given the two reactions
H2S(aq)⇌HS−(aq)+H+(aq),
K1
= 9.39×10−8, and
HS−(aq)⇌S2−(aq)+H+(aq),
K2
= 1.39×10−19,
what is the equilibrium constant Kfinal
for the following reaction?
S2−(aq)+2H+(aq)⇌H2S(aq)


Enter your answer numerically.