①Ni2+:

Cold 10 ml in a 250 ml conical flask supplemented with 100 ml distilled water, 15 ml concentrated ammonia and a tip spoon indicator (ground into powder with ammonium URONATE:NaCl=1:100) was added dropwise to a light brown purple colour (a brownish red to purple colour) with calibrated 0.05 M EDTA (V)

ＣNi2+=5.87MV_ (g/l)

M-molarity of the standard EDTA solution

V-milliliter of standard EDTA solution used

② Reducing agent:NaH2PO2.H2O

Take 5 ml of cold solution in 250 ml capped conical flask, add 1:1 HCl 25 ml and 25 ml 0.1 M demarcated iodine solution, cap place in dark for 0.5 hours (> 25 ℃), open the cap of bottle add 1 ml 1% starch solution, drop with 0.1 M sodium thiosulfate to disappearance of blue color (V2)

ＣNaH2PO2.H2O=10.6(2M1V1-M2V2)_ (g/l)

M1-molarity of the standard iodine solution

V1-milliliters of standard iodine solution used

M2-molarity of the standard sodium thiosulfate solution

V2-number of milliliters of standard sodium thiosulfate solution used

③NaH2PO3:

Remove 5 ml of cold liquor in 250 ml capped conical flask, add 40 ml of distilled water, 5% sodium bicarbonate and 0.1 M demarcated iodine liquor 40 ml, in the dark for 1 h (> 25 ℃), add 98% HAC to pH <4, shake, use 0.1 M sodium thiosulfate to pale yellow, add 1 ml of 1% starch liquor, continue with 0.1 M drip to blue disappearance for 1 min as endpoint V2

ＣNaH2PO3=12.6(2M1V1-M2V2)_ (g/l)

M1-molarity of the standard iodine solution

V1-milliliters of standard iodine solution used

M2-molarity of the standard sodium thiosulfate solution

V2-number of milliliters of standard sodium thiosulfate solution used

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