实验11 三草酸合铁(Ⅲ)酸钾的制备和组成测定
一,实验目的
1.掌握合成K3Fe[(C2O4)3]·3H2O的基本原理和操作技术;
2.加深对铁(Ⅲ)和铁(Ⅱ)化合物性质的了解;
3.掌握容量分析等基本操作.
二,实验原理
本实验以硫酸亚铁铵为原料,与草酸在酸性溶液中先制得草酸亚铁沉淀,然后再用草酸亚铁在草酸钾和草酸的存在下,以过氧化氢为氧化剂,得到铁(Ⅲ)草酸配合物.主要反应为:
改变溶剂极性并加少量盐析剂,可析出绿色单斜晶体纯的三草酸合铁(Ⅲ)酸钾,通过化学分析确定配离子的组成.用KMnO4标准溶液在酸性介质中滴定测得草酸根的含量.Fe3+ 含量可先用过量锌粉将其还原为Fe2+,然后再用KMnO4标准溶液滴定而测得,其反应式为:
5C2O42-+2MnO4-+16H+ ===10CO2↑+2Mn2+ + 8H2O
5Fe2+ + MnO4- +8H+ ===5Fe3+ + Mn2+ + 4H2O
(NH4)2Fe(SO4)2 + H2C2O4 + 2H2O ===FeC2O4·2H2O↓+ (NH4)2SO4 + H2SO4
2FeC2O4·2H2O + H2O2 + 3K2C2O4 + H2C2O4 ===2K3[Fe(C2O4)3]·3H2O
三,实验仪器与试剂
托盘天平,分析天平,抽滤装置,烧杯(100mL),电炉,移液管(25mL),容量瓶(50mL, 100mL),锥形瓶(250mL).
(NH4)2Fe(SO4)2·6H2O,H2SO4(1mol·L-1),H2C2O4(饱和),K2C2O4(饱和),KCl (A. R),KNO3(300g·L-1),乙醇(95%),乙醇—丙酮混合液(1 : 1),K3[Fe(CN)6] (5%),H2O2 (3%).
四,实验步骤
1.三草酸合铁(Ⅲ)酸钾的制备
① 草酸亚铁的制备: 称取5g硫酸亚铁铵固体放在100mL烧杯中,然后加15mL蒸馏水和5~6滴1mol·L-1 H2SO4,加热溶解后,再加入25mL饱和草酸溶液,加热搅拌至沸,然后迅速搅拌片刻,防止飞溅.停止加热,静置.待黄色晶体FeC2O4·2H2O沉淀后倾析,弃去上层清液,加入20mL蒸馏水洗涤晶体,搅拌并温热,静置,弃去上层清液,即得黄色晶体草酸亚铁.
② 三草酸合铁(Ⅲ)酸钾的制备:往草酸亚铁沉淀中,加入饱和K2C2O4溶液10mL,水浴加热313K,恒温下慢慢滴加3%的H2O2溶液20mL,沉淀转为深棕色.边加边搅拌,加完后将溶液加热至沸,然后加入20mL饱和草酸溶液,沉淀立即溶解,溶液转为绿色.趁热过滤,滤液转入100mL烧杯中,加入95%的乙醇25mL,混匀后冷却,可以看到烧杯底部有晶体析出.为了加快结晶速度,可往其中滴加KNO3溶液.晶体完全析出后,抽滤,用乙醇—丙酮的混合液10mL淋洒滤饼,抽干混合液.固体产品置于一表面皿上,置暗处晾干.称重,计算产率.
①KMnO4溶液的标定
准确称取0.13～0.17gNa2C2O4三份,分别置于250mL锥形瓶中,加水50mL使其溶解,加入10mL 3 mol·L-1H2SO4溶液,在水浴上加热到75～85℃,趁热用待标定的KMnO4溶液滴定,开始时滴定速率应慢,待溶液中产生了Mn2+后, 滴定速率可适当加快,但仍须逐滴加入,滴定至溶液呈现微红色并持续30s内不褪色即为终点.根据每份滴定中Na2C2O4的质量和消耗的KMnO4溶液体积,计算出KMnO4溶液的浓度.
2.三草酸合铁酸钾组成的测定
②草酸根含量的测定: 把制得的K3Fe[(C2O4)3]·3H2O在50-60℃于恒温干燥箱中干燥1h,在干燥器中冷却至室温,精确称取样品约0.2-0.3g,放入250mL锥形瓶中,加入25mL水和5mL 1mol·L-1 H2SO4,用标准0.02000 mol·L-1 KMnO4溶液滴定.滴定时先滴入8mL左右的 KMnO4标准溶液,然后加热到343~358K(不高于358K)直至紫红色消失.再用KMnO4滴定热溶液,直至微红色在30s内不消失.记下消耗KMnO4标准溶液的总体积,计算K3Fe[(C2O4)3]·3H2O中草酸根的质量分数 ,并换算成物质的量.滴定后的溶液保留待用.
③铁含量测定: 在上述滴定过草酸根的保留液中加锌粉还原,至黄色消失.加热3min,使Fe3+ 完全转变为Fe2+,抽滤,用温水洗涤沉淀.滤液转入250mL锥形瓶中,再利用KMnO4溶液滴定至微红色,计算K3Fe[(C2O4)3]中铁的质量分数 ,并换算成物质的量.
结论:在1mol产品中含C2O42- mol,Fe3+ mol,该物质的化学式为 .
五,注意事项
1. 水浴40℃下加热,慢慢滴加H2O2.以防止H2O2分解.
2. 减压过滤要规范.尤其注意在抽滤过程中,勿用水冲洗粘附在烧杯和布氏滤斗上的少量绿色产品,否则,将大大影响产量.
Experiment 11 3 ferrous oxalate (Ⅲ) Determination of potassium in the preparation and composition
One purpose of the experiment
1. Grasp synthesis K3Fe [(C2O4) 3] · 3H2O basic principles and operating techniques;
2. Deepen their understanding of iron (Ⅲ) and iron (Ⅱ) compounds understanding of the nature;
3. Master the basic operations such as capacity analysis.
Second, the experimental principle
In this experiment, ferrous ammonium sulfate as raw material, and oxalic acid in acidic solution of ferrous oxalate precipitation was obtained first, and then use potassium oxalate and ferrous oxalate in the presence of oxalic acid, hydrogen peroxide as the oxidant by iron (Ⅲ) oxalate complex. main reaction is:
Change in solvent polarity and add a small amount of salt agents may precipitate the green monoclinic crystals of pure three-ferrous oxalate (Ⅲ) potassium ions by chemical analysis to determine the composition distribution. Standard solution with KMnO4 in acid medium oxalic acid titrated the content of the root. Fe3 + content can be the first to use excessive zinc reduced to Fe2 +, and then use the standard solution of KMnO4 titration and measured, their reaction is:
5C2O42-+2 MnO4-+16 H + === 10CO2 ↑ +2 Mn2 + + 8H2O
5Fe2 + + MnO4-+8 H + === 5Fe3 + + Mn2 + + 4H2O
(NH4) 2Fe (SO4) 2 + H2C2O4 + 2H2O === FeC2O4 · 2H2O ↓ + (NH4) 2SO4 + H2SO4
2FeC2O4 · 2H2O + H2O2 + 3K2C2O4 + H2C2O4 === 2K3 [Fe (C2O4) 3] · 3H2O
Third, experimental equipment and reagents
Pallet scale, analytical balance, filtration devices, beaker (100mL), electric stove, pipette (25mL), volumetric flask (50mL, 100mL), Erlenmeyer flask (250mL).
(NH4) 2Fe (SO4) 2.6 H2O, H2SO4 (1mol · L-1), H2C2O4 (saturated), K2C2O4 (saturated), KCl (A. R), KNO3 (300g · L-1), ethanol (95% ), ethanol - acetone mixture (1: 1), K3 [Fe (CN) 6] (5%), H2O2 (3%).
4, experimental procedures
1. 3 ferrous oxalate (Ⅲ) Preparation of potassium
① Preparation of Ferrous Oxalate: Weigh 5g of solid ammonium ferrous sulfate on the 100mL beaker, then add 15mL of distilled water and 5 to 6 drops of 1mol · L-1 H2SO4, heating dissolved, then add 25mL saturated acid solution, heating and agitating to boiling, then quickly stir a moment, to prevent splashing. stop heating, standing. to be yellow crystals FeC2O4 · 2H2O precipitated decantation, discard supernatant liquid, adding 20mL distilled water crystals, stir and warm, standing, discard supernatant liquid, which was yellow ferrous oxalate crystals.
② Three ferrous oxalate (Ⅲ) Preparation of Potassium: ferrous oxalate to precipitate, by adding saturated K2C2O4 solution 10mL, water bath 313K, constant temperature slowly dropping to 3% H2O2 solution of 20mL, to dark brown precipitate. Edge Bordered stirring, add After the solution was heated to boiling, then add 20mL saturated oxalic acid solution, precipitate immediately dissolved, the solution turns green. hot filtration, the filtrate into 100mL beaker, add 95% ethanol, 25mL, after mixing cooling, you can see the bottom of the beaker and precipitate. In order to accelerate the crystallization rate, which may be dropping to the KNO3 solution. crystal after complete precipitation and filtered, ethanol - acetone mixture of 10mL sprinkling cream cake, drain the mixture. the surface of solid product in a pan, turning the dark to dry. weighing, calculating the yield.
① KMnO4 solution calibration
Weigh accurately 0.13 ~ 0.17gNa2C2O4 three were placed in 250mL conical flask, add 50mL of water to dissolve, adding 10mL 3 mol · L-1H2SO4 solution in a water bath heated to 75 ~ 85 ℃, hot to be calibrated with the KMnO4 titration, titration rate should start slowly, until the solution had a Mn2 +, the titration rate may be appropriate to speed up, but still drops by to join, titration to the solution and continue to 30s showed reddish discoloration shall not end in. According Each titration Na2C2O4 quality and consumption volume of KMnO4 solution, calculate the concentration of KMnO4 solution.
2. 3 ferrous potassium oxalate determination of the composition of
② oxalate content: the system was the K3Fe [(C2O4) 3] · 3H2O at 50-60 ℃ in temperature oven drying 1h, cooled to room temperature in the dryer, accurately weighed sample of about 0.2-0.3g Put 250mL conical flask, add 25mL of water and 5mL 1mol · L-1 H2SO4, with standard 0.02000 mol · L-1 KMnO4 solution titration. titrated around when the first trickle 8mL KMnO4 standard solution, then heated to 343 ~ 358K (not more than 358K) until the purple disappears. then KMnO4 titration hot solution until the reddish does not disappear within in the 30s. note the total consumption volume of standard solution of KMnO4 calculated K3Fe [(C2O4) 3] · 3H2O oxalate root mass fraction, and converted into amount of substance. titration solution retained after the stand-by.
③ Determination of iron content: in the titration of oxalate retention over adding zinc dust reduction solution to the yellow color disappears. Heated 3min, so that the complete transformation of Fe3 + Fe2 +, and filtered, washing with warm water sedimentation. Filtrate into 250mL Erlenmeyer flask , re-use KMnO4 titration to reddish calculated K3Fe [(C2O4) 3] content of iron, and converted into amount of substance.
Conclusion: 1mol products containing C2O42-mol, Fe3 + mol, the substance of the chemical formula.
V. Notes
1. 40 ℃ water bath heating, slowly dropping H2O2. To prevent the H2O2 decomposition.
2. Decompression filter to regulate. Particular attention to the filtration process, do not wash with water in the beaker and Brandt adhesion filter a small amount of green products on the fight, otherwise, it will greatly affect the output.