Question

A researcher creates a new manganese sulfide semiconductor, but does not know the oxidation state of the manganese. She can get the oxidation state from the stoichiometry of of the compound, but this is also unknown. She reacts 0.2088 grams of her semiconductor with excess nitric acid which oxidizes all of the sulfur to sulfate, so (aq), and manganese to permanganate, Mnoz (aq). She then dilutes the acid digestion to 100 mL and uses Inductively-Coupled Plasma-Atomic Emission Spectroscopy to determine that the concentration of permanganate is 0.01251 uM and the concentration of sulfate is 0.04377 um. What is the empirical formula of the original sample? Enter the empirical formula for the unknown compound Enter in AxBy format. If x or y is 1, leave it off (e.g. x =1, then ABy). What is the oxidation state of manganese in the original compound? Leave off the "+". Assume O.N. on sulfur is -2 Give the complete, correct chemical name

Answer 1

Concentration of Mo 04" = [MnO4 ] = 0'01 251 jem =0.01251x106m. 100 ML 0.01251x10 M = (100 X 0'04251x106) mLxM = '1'251x10-6 mLx mol ។ = 10254710-6 10-3, L x mol = 1'251x10 -6 mmol.

2- M. -6 Similarly, concentration of som? [s042-] = 0'04377 MM. = 0'04377x10 100 mL 0.04377x10CM 2 (100% 0'04377x166) mmol 4.377*10 mmol. so mmol ratio of Mr and s = mmol ratio of unor and Soa (because, the oxidation reaction produces same moles of oxidized products). -6 1.251 x 10 : 4377x166 11 1 : 3'5 2:7 ( to make integer) :: Empirical formula Mn 2 S7 2. say, => x OIN of Mn Overall O.N of the compound = 0 2x2 + 7x (-2) = 0 2x x + 14 +7 O.N of un = (+1) correct chemical name will be manganese (Vil) sulphide. Molar mass amount of Mn g/mol. mmol 1' 251 X10-9 mol = (1'251x10 19 of Mn = 54.938 -6 1'251x10 -8 X54.938) g 6.873x10 ºg :: Mass percentage = 6.873x10-84 x 100% 0:2088 g 3:292 x 10 5 %