Equivalent weight = molar mass / n-factor. For acids: n-factor = number of H+ ions donated per molecule (basicity). HCl: 1, H2SO4: 2, H3PO4: 3 (full) or 2 or 1 (partial). For bases: n-factor = number of OH- ions per formula unit. NaOH: 1, Ca(OH)2: 2, Al(OH)3: 3. For oxidising agents: n-factor = total decrease in oxidation state per formula unit. KMnO4 in acid: Mn goes from +7 to +2, n = 5. K2Cr2O7: each Cr goes +6 to +3 (change of 3), 2 Cr atoms, n = 6. For reducing agents: n-factor = total increase in oxidation state. For salts in precipitation/double decomposition: n-factor = total positive (or negative) charge per formula unit.