Wage sample 0.1g (weigh to 0.0001g) in 300ml triangular conical flask, add 1:1 sulfuric acid 5ml, add a little steaming water, heat and dissolve, take off, add 3:1: 1 sulfur phosphate 15 ml, drops of 10% ammonium ferrous sulfate solution to a green, cool to room temperature in cold water with 3% potassium permanganate oxidation to solution is slightly red don’t disappear, then add about 1 gram of solid urea with 1% sodium nitrite is original to solution is bright yellow, and 1 ~ 3 drops, excessive violent oscillation after 30 money clock, add V indicator 3 drops static moment, with standard solution of ammonium ferrous sulfate titration to solution from purple to light green, is the end.
Calculate V2O5% = V.T/G×100
In the formula, V– the number of ml of standard solution of ammonium ferrous sulfate consumed
T– titration of V2O5 for ammonium ferrous sulfate standard solution
G– the weight of the sample
Required Reagents: 1. Sulfuric acid: 1:1
2. Sulfur and Phosphorus Mixed Acid: 3:1:1 (H2SO4: H3PO4: H2O)
3. Ammonium ferrous sulfate: 10% 10g ammonium ferrous sulfate dissolved in 100ml of 5%H2S04 solution
4. Potassium permanganate: 3% must be boiled for several minutes when dissolving, so as not to have KMn04 residues insoluble
5. Urea: Solid
6. Sodium Nitrite: 1% aqueous solution
7. Benzophosphorus Aminobenzoic Acid Indicator: 0.2%, 0.2g soluble in 100ml0.2% sodium carbonate solution.
8. Ammonium ferrous sulfate weighing standard solution — — about 0.03N: weighing ammonium ferrous sulfate [(NH4) 2.Fe(SO4)2.6H2O] 53 grams dissolved in 10 liters of 5% sulfuric acid solution, (this standard solution should be placed in pure aluminum wire can be stored for a long time) placed for several days before calibration.
Calibration steps:
50ml of 0.02N standard potassium dichromate solution was absorbed, 20ml of sulfur-phosphorus mixed acid (H2SO4: H3PO4: H2O = 150:150:700) was added into a 300ml triangle flask, 3 drops of benzoic acid indicator was added, and titrated with prepared ammonium ferrosulfate solution until the solution turned from purple to bright green was the end point. Where: T– titer V2O5 (g/mL) of standard ammonium ferrous sulfate solution
N– potassium dichromate is the equivalent concentration of the quasi-solution
V– mL of absorbed potassium dichromate standard solution
V1– mL of standard solution of ammonium ferrous sulfate consumed
0.09094– V2O5 milligram equivalent number
0.05094– is the milligram equivalent of V
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