Concentration Effect of MgO/K2O Catalyst on Transesterification of Castor Seed (Ricinus communis) Oil: Pengaruh Konsentrasi Katalis MgO/K2O pada Transesterifikasi Minyak Biji Jarak (Ricinus communis). Stannum. 2024;6(2):96-103. doi:10.33019/jstk.v6i2.4692