称取含磷样品0.2000g,溶解后把磷沉淀为MgNH4PO4,此沉淀过滤洗涤再溶解,

最后用0.02000mol/L的EDTA标准溶液滴定,消耗30.00ml,样品中P2O5的百分含(正确答案)

量为(C)。已知M(MgNH4PO4)=137.32g/mol,M(P2O5)=141.95g/mol.

A.42.59%

B.41.20%

C.21.29%

D.20.60%

62在pH=13时,用铬黑T作指示剂,用0.010mol/L的EDTA滴定同浓度的钙离子,终点时pCa=4.7,则终点误差为(D)。

A.-0.1%

B.-0.2%

C.-0.3%

D.一0.4%