Two free a cappella performances will take place this weekend at the Montauk Library. Tomorrow evening at 7:30, the Chickpeas, a quintet consisting of Liz Sarfati, Marcia Previti, Lisa Shaw, Deb Coen, and Jane Hastay, will perform a program of traditional and popular songs by composers ranging from Harold Arlen to Sammy Cahn and Jule Styne to Bob Dylan.