配平下列反应方程式 (3) K 2 Cr 2 O 7 + KI + H 2 SO 4 → K 2 SO 4 + Cr 2 (SO 4 ) 3 + I 2 + H 2 O (7) P + NaOH + H 2 O → NaH 2 PO 2 + PH 3 ( 12 ) KMnO 4 +NaNO 2 +KOH →K 2 MnO 4 +NaNO 3 +H 2 O (16) As 2 S 3 + HNO 3 ( 浓 ) → H 3 AsO 4 +NO + H 2 SO 4 (18) H 2 O 2 + Cr 2 SO 4 + KOH → K 2 CrO 4 + K 2 SO 4 + H 2 O (23) KIO 3 + KI + H 2 SO 4 → I 2 + K 2 SO 4 + H 2 O ( 28 ) FeS 2 +O 2 = Fe 3 O 4 +SO 2