Ammonia has Kb=1.8×10−5. For a 0.0010 M aqueous solution of NH3, a student assumes the equilibrium concentration of NH3 equals 0.0010 M when calculating pH. Which choice best describes both the validity of the assumption and the direction of the resulting pH error?
a) Assumption valid; calculated pH will be too low
b) Assumption valid; calculated pH will be too high
c) Assumption invalid; calculated pH will be too high
d) Assumption invalid; calculated pH will be too low