Experiment 1

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Dec 16, 2024

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Experiment 1: Synthesis of (Cu(NH3)4)SO4ProcedureWeigh out 3.5 grams of copper sulfate pentahydrate. Transfer the solid to a 125ml Erlenmeyerflask and add 7.5 ml of water. Heat the flask to dissolve the solid, and then cool to roomtemperature. Add 7.5 ml of NH3to the solution, a few ml at a time. The solution shouldimmediately change from the pale-blue color of [Cu(H2O)4]2+to the intense blue of[Cu(NH3)4]2+. An initial precipitate has dissolved and a solution with no trace of cloudiness isobtained.To this solution, add 7.5 ml of 95% ethanol. An immediate precipitate of [Cu(NH3)4]SO4shouldbe observed. Filter the resulting solid through a Buchner funnel using suction filtration and washwith two additional portions of 95% ethanol. Allow the solid to air dry and obtain the mass ofproduct obtained.Titration of the sample Obtain three 125 ml Erlenmeyer flasks and burette. Weigh out approximately 0.5-0.75 grams ofsolid [Cu(NH3)4]SO4in to each flask. It is a good idea to use a slightly different mass for eachtrial. Add 7.5-10ml of water to each flask and swirl to dissolve the solid. The resulting solutionmay appear cloudy. Since this solution does not contain an excess of NH3, some of thecoordinate NH3will be replaced with H2O. This result in the formation of neutral species such as[Cu(NH3)2(H2O)2](OH)2or [Cu(NH3)2(OH)2], which are most likely responsible for thecloudiness of the solution.The titration may be conducted like a standard acid-base titration. Slowly swirl the flask by handas the HCl is added. The HCl may be added fairly rapidly at the beginning of the titration.However, this must be slowed to a drop wise addition near the endpoint of the titration. A fairlypronounced color change from the deep-bluecolor of [Cu(NH3)4]2+to the pale-bluecolor[Cu(H2O)6]2+should occur at the endpoint of the titration. The resulting solution should be clearwith no trace of cloudiness. Repeat the procedure for the second and third flasks. Based upon thevolume of HCl added and the morality of the HCl, calculate the number of moles of NH3andmass percent of NH3 in each sample.

Report your observation using the following formatflask 1flask2flask3mass of [Cu(NH3)4]SO4Initial volume of buretteFinal volume of buretteVolume of HCl dispensedMoles of HCl dispensedMoles of NH3 in sampleMass of NH3 in sampleMass percent of NH3Average mass percentQuestions1.For each of the following formulas, calculate the mass percent of NH3A. [Cu(H2O)2(NH3)4]SO4B. [Cu(H2O)(NH3)5]SO4C. [Cu(NH3)6]SO42.Refer to the formulas listed above (question 1).based up on the theoretical mass percent ofNH3calculated in this experiment, which formula to you think is correct?3.Give a reason why your mass percent may not exactly match one of the values calculated inQ1.