added ap chem things to memorize

notes/chem/chem_memo.txt

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+== POLYATOMIC IONS ==
++1: NH4 (Ammonium), H3O (Hydronium)
+-1: C2H3O2, BrO3, ClO3, ClO2, CN, HCO3, OH, ClO, IO3, NO3, NO2, ClO4, MnO4, SCN
+-2: CO3, CrO4, Cr2O7, C2O4, SO4, SO3, S2O3
+-3: AsO4, BO3, PO4
+
+== VARIABLE CATIONS ==
+Cu, Hg: 1, 2
+Fe, Cr, Co, Ni, Mn: 2, 3
+Pb, Sn: 2, 4
+Sb, Bi: 3, 5
+
+== FIXED CATIONS ==
+Zn: 2, Ag: 1, Cd: 2
+
+== STRONG ACIDS ==
+HCl, HBr, HI, HNO3, HClO4, HClO3, H2SO4
+
+== SOLUBILITY ==
+SOLUBLE: Gp1, NH4, NO3, Acetate, ClO3, ClO4
+HALIDES: Soluble EXC: Ag, Pb, Hg2(2+)
+SULFATES: Soluble EXC: Ba, Sr, Ca, Hg2(2+), Pb
+SULFIDES: Insol EXC: Ba, Ca, Sr
+OH: Insol EXC: Gp1, Ba, Sr, Ca