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Scan_Doc0139 - AdditionaL Exercises 231 119 The nitrogen...

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119. The nitrogen content oforganic compounds can be determined bytheDumas method. Thecompound inquestion isfirstreacted bypassage over hot CuO(s): Hot Compound ----c> N 2 (g) + COig) + H 2 0(g) (uo(.<) The product gas isthen passed through aconcentrated solution ofKOH toremove theCO 2 ,After passage through theKOH so- lution, thegas contains N2andissaturated with water vapor. In agiven experiment a0.253-g sample ofacompound produced 31.8 mL N2saturated with water vapor at 25°C and 726 torr. What isthemass percent ofnitrogen inthecompound? (Theva- por pressure ofwater at25°C is23.8 torr.) 120. An organic compound containing only C, H, and N yields the following data. i. Complete combustion of35.0mgofthecompound produced 33.5 mgCO 2 and 41.1 mg H 2 0. ii. A 65.2-mg sample of the compound was analyzed for nitrogen by the Dumas method (see Exercise 119), giving 35.6 mL N2at740. torr and 25°C. iii. The effusion rate ofthe compound as agas was measured andfound tobe24.6mL/min. Theeffusion rateofargon gas, under identical conditions, is26.4 mUmin. What isthe molecular formula ofthecompound? 121. Atmospheric scientists oftenusemixing ratios toexpress thecon- centrations of trace compounds in air. Mixing ratios are often expressed asppmv (parts per million volume): f volofXatSTP 6 ppmv 0 X = X 10 total volofairatSTP
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