Question

Which of the following is/are false?

• A. Na2Cr2O7 is used as a primary standard in volumetric analysis.
• B. Potassium permanganate in excess on treatment with conc. H2SO4 forms manganese heptoxide
• C. Phosphine, arsine and stibine all precipitates silver from silver nitrate
• D. From kipp's apparatus waste ferric sulphate and ferrous sulphate mixture is obtained when air or oxygen is passed for longer time.

Answer 1

Answer: (A)

Na2Cr2O7 is used as a primary standard in volumetric analysis.

Answer 2

(1) Na2 Cr2O7 is not used as primary standard because it is hygroscopic in nature.

(2) 2KMnO4 + 3H2SO4 $\longrightarrow$ 2KHSO4 + (MnO3)2SO4 + 2H2O

(MnO3)2SO4 + H2O $\longrightarrow$Mn2O7 + H2SO4

(3) PH3 + 6AgNO3 + 3H2O $\longrightarrow$ 6Ag + 6HNO3 + H3PO3

AsH3 + 6AgNO3 + 3H2O $\longrightarrow$ 6Ag + 6HNO3 + H3AsO3

(4) 3FeS2 + 2H2O + 11O2 $\longrightarrow$2FeSO4 + Fe2(SO4)3 + 2H2SO4