If the conjugation adds an 'e' to the stem, then the 'c' is replaced by 'qu'

platicar - to chat
mascar - to chew
amplificar - to amplify
disecar - to dissect
electrificar - to electrify
clarificar - to clarify
abroncar - to tell off
apalancar - to open with lever
calcificarse - to calcify
aparcar - to park, to shelf
amoscarse - to get in a huff
suplicar - to plead
justificar - to justify
plastificar - to plasticize
abanicarse - to fan oneself
achacar - to attribute
blocar - to block
complicar - to complicate
achicar - to make smaller, to bail out, to drain
cualificar - to qualify
adjudicar - to award
certificar - to confirm
ahorcarse - to hang oneself (judas)
ahuecar - to cub, to hollow out
conculcar - to infringe, to break
contraatacar (yes there are two a's together)- to counterattack
derrocar - to bring down, to overthrow
desatascar - to unblock
desatrancar - to unbolt, to unblock
edificar - to build
engrescar - to incite, to "egg on"
fabricar - to manufacture, to build, to make
enroscar - to screw in
entresacar - to pick out
explicar - to explain
falsificar - to forge
intensificar - to intensify
lacar - to lacquer
marcar - to mark
mascar - to chew
picar - to bite
placar - to tackle
plastificar - to plasticize
provocar - to incite
refrescar - to refresh, to chill
sacar - to take out
tocar - to touch, to play (instrument)
unificar- to unite