This experiment is from the official website of Southern Medical University
Operation method
Experiments on the preparation of ammonium ferrous sulfate
Principle
Iron filings are easily soluble in dilute sulfuric acid, generating ferrous sulfate: Fe + H2SO4= FeSO4+ H2↑ ferrous sulfate and the equivalent mass of ammonium sulfate in aqueous solution, that is, the generation of a smaller solubility of light blue ammonium ferrous sulfate FeSO4-(NH4)2SO4-6H2O complex crystals. FeSO4+ (NH4)2SO4+ 6H2O = FeSO4-(NH4 )2SO4-6H2O Generally ferrous salts are easily oxidized in air, but the formation of complex salts is more stable and not easily oxidized.
Materials and Instruments
Iron filings (NH4)2SO4 H2SO4 HCl Na2CO3 KSCN Move I. Purification of iron filings Caveat (1) Iron shavings should be crushed first and all submerged in 20mL of 3mol-L-1 H2SO4 solution while not shaking the conical flask violently to prevent iron from oxidizing when exposed to air.(2) Replenish water while heating in step 2, but do not add too much water to keep the pH below 2. If the pH is too high, Fe2+ is easily oxidized to Fe3+.(3) Filtration under reduced pressure while hot in step 2, two layers of filter paper can be used at the same time in order to prevent permeation, and the filtrate can be quickly poured into the pre-dissolved (NH4)2SO4 solution to prevent the oxidation of FeSO4. For more product details, please visit Aladdin Scientific website.
Filter flasks Brinell's funnel conical flasks evaporating dishes surface dishes measuring cylinders platform scales water baths suction tubes cuvettes colorimetric tubes
Weigh 6g of iron filings, put in a conical flask, add 40mL 10% Na2CO3 solution, heating on a water bath for 10min, decantation method to remove the lye, water to rinse the lye on the iron filings to prevent Na2SO4 crystals from mixing into the FeSO4 after adding H2SO4.
Second, the preparation of ferrous sulfate
Add 40mL of 3mol-L-1 H2SO4 ① to the conical flask with iron filings, heat it on a water bath, so that the iron filings and sulfuric acid react completely (about 50min), water and H2SO4 solution ② should be added to the conical flask from time to time (always keep the pH of the reaction solution below 2), in order to replenish the water that has been evaporated, and then filter it under reduced pressure while it is still hot ③, and retain the filtrate. Pre-calculate the theoretical yield of ferrous sulfate produced from 6 g of iron filings.
Third, the preparation of ammonium ferrous sulfate
According to the theoretical yield of ammonium ferrous sulfate calculated above, approximately in accordance with the mass ratio of FeSO4 to (NH4)2SO4 of 1:0.75, several grams of solid ammonium sulfate were weighed and dissolved in an evaporating dish containing 20 mL of slightly heated distilled water, and then the hot filtrate mentioned above was poured into it and mixed. Then it was heated and evaporated on a water bath, concentrated until a crystal film appeared on the surface, placed to let it cool slowly, that is, ammonium ferrous sulfate crystals. The mother liquor was removed by filtration under reduced pressure, the crystals were placed on absorbent paper and drained, the color and shape of the crystals were observed, and finally weighed and the yield was calculated.
Inspection of products
1. Analysis of trace iron (Ⅲ)
Weigh 1.0 g of sample in 25 mL colorimetric tube, add 15 mL of distilled water without oxygen to dissolve, then add 2 mL of 3 mol-L-1HCl and 1 mL of saturated KSCN solution, continue to add distilled water without oxygen to the 25 mL scale, shake well, and the standard solution for visual colorimetry, to determine the grade of the product.
2. Preparation of standard solution
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, and the same treatment as the sample, and finally diluted to 25.00 mL.