One of the experiments in inorganic chemistry laboratory course involved the syn

Question

One of the experiments in inorganic chemistry laboratory course involved the synthesis and characterization of a copper-ammonia complex of the type Cu_2 (NH_3)_y (SO_4)_z, aH_2 O. Student Jack synthesized the complex and performed chemical analyses to determine the exact formula for the complex. From spectroscopic and gravimetric analyses. Jack found that the weight percentages of Cu (63.55 amu) and SO_4^2+ (96.06 amu) were 24.10% and 36 40%, respectively. He then performed volumetric analysis for ammonia NH_3 (17 03 amu). In the volumetric analysis. Jack first weighed out 0 982 g of the complex, and dissolved it in about 30 mL of water. After adding 10 drops of methyl orange indicator to the solution, he then titrated the solution with a standard hydrochloric acid solution. At the end point he used up 30.06 mL of 0.5000 M HCl solution. What was the chemical formula based on Jack's data?

Explanation / Answer

moles HCl used for NH3 titration = 0.5 M x 30.06 ml = 15.03 mmol

mass NH3 present in complex = 15.03 x 17/1000 = 0.2555 g

% NH3 is complex = 0.2555 x 100/0.9882 = 13.31%

moles Cu = 0.9882 x 0.241/63.55 = 0.004 mol

moles SO4^2- = 0.9882 x 0.364/96.06 = 0.004 mol

moles NH3 = 0.258/17 = 0.015 mol

moles H2O = 0.9882 x 0.134/18 = 0.007 mol

Divide by smallest factor

Cu = 0.004/0.004 = 1

SO4^2- = 0.004/0.004 = 1

NH3 = 0.015/0.004 = 4

H2O = 0.007/0.004 = 2

So,

chemical formula for complex = Cu(NH3)2SO4.2H2O

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