Preparation Experiment of Ferrous Ammonium Sulfate

Preparation Experiment of Ferrous Ammonium Sulfate

Iron filings are easily soluble in dilute sulfuric acid to form ferrous sulfate:
Fe + H2SO4 = FeSO4 + H2 ↑
Ferrous sulfate interacts with the same amount of ammonium sulfate in an aqueous solution, that is, a light blue ferrous ammonium sulfate FeSO4·(NH4)2SO4·6H2O composite crystal with less solubility is formed.
FeSO4 + (NH4)2SO4 + 6H2O = FeSO4·(NH4)2SO4·6H2O
Generally, ferrous salts are easily oxidized in the air, but they are relatively stable after forming double salts and are not easy to be oxidized.
Materials and Instruments
Iron filings (NH4)2SO4 H2SO4 HCl Na2CO3 KSCN
Suction filter bottle, Buchner funnel, conical flask, evaporating dish, watch dish, graduated cylinder, scale, water bath, pipette, colorimetric tube
1. Purification of iron filings
Weigh 6g of iron filings, put them in a conical flask, add 40 mL of 10% Na2CO3 solution, heat on a water bath for 10 minutes, remove the lye by decantation, and rinse the lye on the iron filings with water to prevent the formation of H2SO4. Na2SO4 crystals are mixed into FeSO4.
Second, the preparation of ferrous sulfate
Add 40mL of 3mol·L-1 H2SO4

① to the conical flask containing iron filings, heat on a water bath to make the iron filings react with sulfuric acid completely (about 50min), and add water and H2SO4 solution to the conical flask from time to time

② (required Always keep the pH value of the reaction solution below 2) to supplement the evaporated water, filter

③ while hot under reduced pressure, and retain the filtrate. The theoretical yield of 6g iron filings to form ferrous sulfate is calculated in advance.
3. Preparation of ferrous ammonium sulfate
According to the theoretical yield of ferrous ammonium sulfate calculated above, approximately according to the mass ratio of FeSO4 and (NH4)2SO4 is 1: 0.75, weigh several grams of solid ammonium sulfate, dissolve in an evaporating dish containing 20 mL of slightly hot distilled water , and then pour the above hot filtrate into it and mix. Then, it is heated and evaporated on a water bath, concentrated until a crystal film appears on the surface, and it is left to cool slowly to obtain ferrous ammonium sulfate crystals. The mother liquor was removed by filtration under reduced pressure, the crystals were blotted dry on absorbent paper, the color and shape of the crystals were observed, finally weighed and the yield was calculated.
4. Product inspection
1. Analysis of Trace Iron(Ⅲ)
Weigh 1.0 g of sample into a 25 mL colorimetric tube, add 15 mL of oxygen-free distilled water to dissolve, then add 2 mL of 3 mol L-1HCl and 1 mL of saturated KSCN solution, and continue to add oxygen-free distilled water to the 25 mL mark line, shake well, and perform visual colorimetry with the standard solution to determine the product grade.
2. Prepare standard solutions
Take Fe3+ solution containing the following mass: 0.05 mg of grade I reagent, 0.10 mg of grade II reagent, 0.20 mg of grade III reagent, treated in the same way as the sample, and finally diluted to 25.00 mL.
(1) The iron filings should be crushed first, and all of them should be immersed in 20mL of 3mol·L-1 H2SO4 solution. At the same time, do not shake the conical flask vigorously to prevent the iron from being oxidized when exposed to the air.
(2) In the second step, add water while heating, but do not add too much water and keep the pH below 2. If the pH is too high, Fe2+ is easily oxidized to Fe3+.
(3) For the filtration while hot under reduced pressure in step 2, two layers of filter paper can be used at the same time to prevent diafiltration, and the filtrate is quickly poured into the pre-dissolved (NH4)2SO4 solution to prevent the oxidation of FeSO4.

Preparation Experiment of Ferrous Ammonium Sulfate

Post time: Apr-26-2022

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