- The Preparation And Analysis Of An Iron Oxalate Complex K3fe C2o4 3 Nh20 Introduction You Won T Deal Fully With The Theo 1 (92.17 KiB) Viewed 93 times
- The Preparation And Analysis Of An Iron Oxalate Complex K3fe C2o4 3 Nh20 Introduction You Won T Deal Fully With The Theo 2 (99.73 KiB) Viewed 93 times
THE PREPARATION AND ANALYSIS OF AN IRON-OXALATE COMPLEX K3Fe(C2O4)3-nH20 INTRODUCTION You won't deal fully with the theory of transition metals this year, but this experiment's a good one for learning laboratory manipulations and it's got interesting colours! The title complex crystallises as a very bright green hydrate - almost a fluorescent colour. The complex is indeed light-sensitive, decomposing slowly in daylight, so keep the product covered up. The experiment actually is done over 2 weeks, first the synthesis, and then the analysis. The final analysis needs a little explanation. The idea is to analyse for oxalate, then for iron, to check that there are indeed three oxalates to every one iron, and lastly to estimate the RMM of the complex and work out how many water molecules there are which crystallise with it. First the oxalate is oxidised to carbon dioxide using permanganate 16H* + 5 C2042 + 2 MnO4 → 2 Mn2+ + 8 H20 + 10 CO2 5.1 and two electrons are consumed for every oxalate. Oxalates are toxic. The synthesis uses hydrogen peroxide which can cause temporary itchy white skin blotches. Rinse your hands after using these chemicals. PROCEDURE: SYNTHESIS (G5) Work in pairs. Dissolve 15 g of ammonium ferrous sulphate (NH4) Fe(SO4)2-6H20 in 50 ml of hot water. Make up a solution of 10 g oxalic acid in 100 ml hot water. Add 75 ml of this to the above solution, saving 25 ml for later.* Cautiously heat to boiling, and allow the yellow granular precipitate of Fecz04-H,0 to settle. Decant off most of the hot (CARE!) liquid and allow the rest to cool. Wash the solid a few times with about 30 ml water, by decantation (which means leave the solid to settle, then pour off as much water as you dare) and retain the solid for the next stage. Prepare a solution of 10 g of potassium oxalate monohydrate K2C2O4 H20 in 30 ml water, and add the yellow ferrous oxalate to this. Warm to 35 – 45° C and add slowly from a measuring cylinder 25 ml of ’20 volume' hydrogen peroxide solution, stirring steadily. Heat the brown mixture to boiling, and add, in one portion, most of the oxalic acid solution (retained from above*). Keeping the solution near to boiling, add further small amounts of oxalic acid to obtain a bright green solution, but avoid adding much more once this stage is reached. Filter the hot solution by gravity and add 30 ml of methylated spirits, and let cool slowly to room temperature, and then in ice, keeping covered and away from bright light. Collect by suction filtration, wash with a little acetone, cover, and dry at the pump. Keep away from light. Store the complex for analysis on the following week. 6.1 PROCEDURE: ANALYSIS (G6) Accurately weigh about 0.5 g of your title complex, and dissolve in about 20-30 ml dilute sulphuric acid warmed strongly over a water bath or flame (the less solvent the better, but don't be too fastidious). Keep the solution hot, and titrate with the standard 0.02 M permanganate to a pink end-point. The reaction is slow-keep it above 80°C for best results. Note the titre at the permanent pale pink tinge.
In the box below, enter the mass of the weighing vessel and iron-oxalate complex/ g. 1.502 In the box below, enter the mass of the weighing vessel after transfer/ g. 1.031 In the box below, enter the mass of iron-oxalate complex weighed out for analysis/ g. 0.471g In the box below, enter the concentration of the permanganate solution used (should be 0.05 M but may differ)/ M. Assume this number is exact, i.e. known to infinite significant figures. 0.05 In the box below, enter the titre of exactly 0.05 M permanganate solution delivered, to the nearest 0.05 ml. 24.55 Calculate and enter the amount of permanganate used/mol. Next, calculate the amount of oxalate this permanganate destroyed (you'll need to derive and balance the chemical equation first)/ mol. How many moles of oxalate are there in every mole of complex? Enter your integer value below ('integer' means it has to be a whole number). Hence, calculate and enter the amount of moles of complex weighed out for analysis/ mol. From this value calculate and enter the Relative Molar Mass (RMM) of the complex/ g mor? Calculate and enter the RMM of the KzFe(C2O4)3 unit in the absence of any waters of crystallisation/ g mol?. RAMs: Fe 55.85; K 39.10; C 12.01; 0 16.00; H 1.01. Finally, from the discrepancy between the values obtained, calculate and enter the number of water molecules crystallising in the complex (i.e. the value of n in KzFe(C2O4)3.n(H20)) Your value need not be an integer. Enter the number of significant figures applicable to quoting the value of n. Enter an integer. There are 9 boxes which involve calculation and correct reporting shown in heavy outlines. These score 10 marks each. 10 marks will also be awarded on the closeness of the value reported for n, compared to the accepted value.