First, the experimental purpose
1. Master the basic principle and operation technology of synthesizing K3Fe [(C2O4) 3] 3H2O;
2. Deepen the understanding of the properties of iron (Ⅲ) and iron (Ⅱ) compounds;
3. Master basic operations such as ability analysis.
Second, the experimental principle
In this experiment, ammonium ferrous sulfate was used as raw material to react with oxalic acid in acidic solution to prepare ferrous oxalate precipitate, and then ferrous oxalate was used in the presence of potassium oxalate and oxalic acid, and hydrogen peroxide was used as oxidant to obtain iron (ⅲ) oxalate complex. The main reactions are as follows:
Green monoclinic pure potassium ferric oxalate (Ⅲ) can be precipitated by changing the polarity of solvent and adding a small amount of salting-out agent, and the composition of coordination ions can be determined by chemical analysis. The content of oxalate can be determined by titration with potassium permanganate standard solution in acidic medium. Fe3+ content can be reduced to Fe2+ with excessive zinc powder, and then titrated with KMNO _ 4 standard solution. The reaction formula is as follows:
5c2o 42-+2mno 4-+ 16H+= = = 10co 2 ↑+ 2mn 2 ++ 8H2O
5fe 2 ++ MnO 4-+8H+= = = 5fe 3 ++ Mn2 ++ 4H2O
(NH4)2Fe(SO4)2+h2c2o 4+2H2O = = = fec2o 4·2H2O↓+(NH4)2so 4+h2so 4
2 fec2o 4·2H2O+H2O 2+3k 2c2o 4+h2c2o 4 = = = 2k 3[Fe(c2o 4)3]3H2O
Third, experimental instruments and reagents
Tray balance, analytical balance, suction filter, beaker (100mL), electric stove, pipette (25mL), volumetric flask (50mL, 100mL) and conical flask (250mL).
(NH4) 2Fe (SO4) 2 6H2O, H2SO4 (1mol L-1), H2C2O4 (saturated), K2C2O4 (saturated), KCl (a.r), Kno3 (300g L-65433.
Fourth, the experimental steps
Preparation of 1. potassium ferric oxalate
① preparation of ferrous oxalate: weigh 5g ammonium ferrous sulfate solid in a beaker of 100mL, then add 15mL distilled water and 5-6 drops of 1 mol L- 1 H2SO4, heat and dissolve, then add 25mL saturated oxalic acid solution, heat and stir until boiling, and then quickly stir for a while to prevent it. Stop heating. Let it stand. After the yellow crystal FeC2O4 2H2O is precipitated, it is decanted, the supernatant is discarded, 20mL distilled water is added to wash the crystal, the temperature is raised by stirring, and the supernatant is discarded to obtain yellow crystal ferrous oxalate.
② Preparation of potassium iron (Ⅲ) oxalate: Add 10mL saturated K2C2O4 solution to ferrous oxalate precipitate, heat it to 3 13K in water bath, and slowly drop 20mL 3% H2O2 solution at constant temperature, and the precipitate turns dark brown. Stir while adding, heat the solution to boiling after adding, then add 20mL of saturated oxalic acid solution, the precipitate will dissolve immediately, and the solution will turn dark brown. Transfer the filtrate to a 100mL beaker, add 25ml 95% 95% ethanol, mix well, and then cool. You can see that there is crystal precipitation at the bottom of the beaker. In order to accelerate crystallization, potassium nitrate solution can be added dropwise. After the crystal is completely precipitated, the filter cake is filtered, sprayed with 10mL ethanol-acetone mixed solution, and the mixed solution is discharged. Put the solid product on the watch mirror and dry it in the dark.
① ① Calibration of potassium permanganate solution
Accurately weigh three parts of 0.13 ~ 0.17 gna2c2o4, put them in a 250mL conical flask, add 50mL water to dissolve them, add 10 ml 3 mol L- 1H2SO4 solution, heat them to 75 ~ 85℃ in a water bath, and use KM when they are hot. After Mn2+ is produced in the solution, the titration speed can be appropriately accelerated, but it still needs to be added drop by drop until the solution turns red and does not fade for 30 seconds. According to the mass of Na2C2O4 in each titration and the volume of KMnO4 solution consumed, the concentration of KMnO4 solution was calculated.
2. Determination of components of potassium ferrous oxalate
② Determination of oxalate content: dry the prepared K3Fe [(C2O4) 3] 3H2O in a constant temperature drying oven at 50-60℃ for 65438+0h, cool it to room temperature in a dryer, accurately weigh about 0.2-0.3g of the sample, put it in a 250mL conical flask, and add 25mL of water and 5ml1mol L-. Titrate with standard 0.02000 mol L- 1 potassium permanganate solution. When titrating, add about 8mL of potassium permanganate standard solution dropwise, and then heat it to 343~358K (not higher than 358K) until the purple color disappears. Titrate the hot solution with KMnO4 until the red color does not disappear within 30s. Write down the total volume of consumed kmno4 standard solution and calculate K3fe [
③ Determination of iron content: add zinc powder to the retained solution of oxalic acid titration until the yellow color disappears, heat for 3min to completely convert Fe3+ into Fe2+, filter, and wash the precipitate with warm water. Transfer the filtrate to a 250mL conical flask, titrate it to red with KMnO4 solution, calculate the mass fraction of iron in K3Fe[(C2O4)3], and convert it into the amount of substance.
Conclusion: The product of 1mol contains C2O42-mol and Fe3+mol, and its chemical formula is.
Verb (abbreviation of verb) matters needing attention
1.40℃ water bath heating, slowly dropping H2O2 to prevent H2O2 decomposition.
2. Decompression filtration should be standardized. When filtering, pay special attention not to rinse a small amount of green products attached to beakers and Brewster's filter barrels with water, otherwise the output will be greatly affected.
Experiment/preparation of kloc-0/13 ferrous oxalate and determination of potassium in its composition.
One purpose of the experiment
1. Master the basic principle and operation skills of synthesizing K3Fe [(C2O4) 3] 3H2O;
2. Deepen their understanding of the properties of iron (Ⅲ) and iron (Ⅱ) compounds;
3. Master basic operations such as ability analysis.
Second, the experimental principle
In this experiment, ammonium ferrous sulfate was used as raw material and precipitated with oxalic acid in acidic solution to obtain ferrous oxalate, and then potassium oxalate and ferrous oxalate were used in the presence of oxalic acid and hydrogen peroxide as oxidant to form ferrous oxalate complex. The main reaction is:
The green monoclinic crystal of pure potassium ferrous oxalate can be precipitated by changing the polarity of solvent and adding a small amount of salt-forming agent, and its composition distribution can be determined by chemical analysis. Titrate the content of root with potassium permanganate standard solution in acid medium oxalic acid. Fe3+content can be reduced to Fe2+by excessive zinc, and then titrated with KMnO4 standard solution and measured. Their reactions are as follows:
5c2o 42-+2 MnO 4-+ 16h+= = = 10co 2 ↑+ 2 Mn2 ++ 8H2O
5fe 2 ++ MnO 4-+8h+= = = 5fe 3 ++ Mn2 ++ 4H2O
(NH4)2Fe(SO4)2+h2c2o 4+2H2O = = = fec2o 4·2H2O↓+(NH4)2so 4+h2so 4
2 fec2o 4·2H2O+H2O 2+3k 2c2o 4+h2c2o 4 = = = 2k 3[Fe(c2o 4)3]3H2O
Third, the experimental equipment and reagents
Tray scale, analytical balance, filtering device, beaker (100mL), electric stove, pipette (25mL), volumetric flask (50mL, 100mL) and conical flask (250mL).
(NH4) 2Fe (SO4) 2.6 H2O, H2SO4 (1mol L- 1), H2C2O4 (saturated), K2C2O4 (saturated), KCl (A. R), KNO3 (300g L- 1).
4. Experimental procedures
Preparation of 1.3 potassium ferrous oxalate
① preparation of ferrous oxalate: weigh 5g of solid ammonium ferrous sulfate in a beaker of 100mL, then add 15mL distilled water and 5-6 drops of 1mol L- 1 H2SO4, heat and dissolve, then add 25mL saturated acid solution, heat and stir until boiling, and then stir quickly for a while to prevent splashing. Stop heating and stand. After the yellow crystal FeC2O4 2H2O is separated out, decant, discard the supernatant, add 20mL of distilled water for crystallization, stir and warm, let stand, and discard the supernatant to obtain yellow ferrous oxalate crystal.
(2) Preparation of potassium iron (Ⅲ) oxalate: ferrous oxalate is precipitated, by adding saturated K2C2O4 solution 10mL, water bath 3 13K, and slowly dropping it to 20mL of 3% H2O2 solution at constant temperature until it is dark brown. Stir while adding, heat the solution until it boils, then add 20mL of saturated oxalic acid solution, the precipitate will dissolve immediately, and the solution will turn green. Filter while it is hot, pour the filtrate into a 100mL beaker, add 25ml 95% 95% ethanol, and after stirring and cooling, you can see precipitation at the bottom of the beaker. In order to speed up the crystallization, it may drop into KNO3 solution. After the crystals are completely precipitated and filtered, the mixture of 10mL ethanol-acetone is sprayed on the cream cake, and the mixture is drained. The surface of the solid product in the pot is turned dark and dried. Weigh and calculate the output.
① Calibration of potassium permanganate solution
Accurately weigh 0.13 ~ 0.17gna2c2o4 into 250mL conical flask, add 50mL water to dissolve, add 10mL 3 mol L- 1H2SO4 solution, heat it to 75 ~ 85℃ in water bath, and use it when it is hot. Until there is Mn2+in the solution, the titration speed can be appropriately accelerated, but it is still necessary to add it drop by drop. According to the mass of Na2C2O4 titrated each time and the consumption of KMnO4 solution, the concentration of KMnO4 solution can be calculated.
2.3 Determination of components of potassium ferrous oxalate
② Oxalate content: The system is that K3Fe [(C2O4) 3] 3H2O is dried in a constant temperature oven at 50-60℃ for 65438+0h, cooled to room temperature in a dryer, accurately weighed about 0.2-0.3g of the sample, placed in a 250mL conical flask, and added with 25mL of water and 5ml1mol L-/kloc. When titrating, drop 8 ml of KMnO4 standard solution, and then heat it to 343 ~ 358K (no more than 358K) until the purple disappears. Then titrate the hot solution with KMnO4 until the reddish color does not disappear within 30s. Write down the total consumption volume of KMnO4 standard solution, calculate the mass fraction of K3Fe [(C2O4) 3] 3H2O oxalate, and convert it into the amount of substance. Titration solution retained after standby.
③ Determination of iron content: When titrating oxalic acid, add zinc powder to reduce the solution until the yellow color disappears. Heating for 3min to completely convert Fe3+Fe2+,filtering, and washing the precipitate with warm water. Filter it into a 250mL conical flask, then titrate it with KMnO4 until it is reddish, calculate the iron content of K3Fe [(C2O4) 3], and convert it into the amount of substance.
Conclusion: The product of 1mol contains C2O42-mol and Fe3+mol, and the chemical formula is.
Verb (abbreviation for verb) notes
1.40℃ water bath heating, slowly drop H2O2. Prevent H2O2 from decomposing.
2. Adjust the decompression filter. Pay special attention to the struggle between the beaker and a small amount of green products on the Brandt filter during filtration, otherwise, it will greatly affect the output.