The nitrogen content of organic compounds can be determined by the Dumas method.
ID: 574607 • Letter: T
Question
The nitrogen content of organic compounds can be determined by the Dumas method. The compound in question is first passed over hot Cuo(s): Compound N2(g) + CO2(g) + H2O(g) The gaseous products are then passed through a concentrated aqueous KOH solution to remove the Co2. CuO(s) The remaining gas contains N2 and water vapor A 0.138-g sample of a compound was treated as above, producing 89.9 mL of N2 saturated with water vapor at 25 °C and 754.6 torr What is the mass percent of nitrogen in the compound? (The vapor pressure of water at 25 °C is 23.8 torr.)Explanation / Answer
pressure P = 754.6 torr
Partial pressure of N2, p = 754.6 - 23.8
= 730.8 torr x 1atm/760torr
= 0.9615 atm
Moles of N2 gas
n = pV/RT
= (0.9615 atm)(0.0899 L)/(0.0821 L-atm/mol*K)(298.15 K)
= 0.003532 mol of N2
Mass of N2 = moles x molecular weight
= 0.003532 x 28
= 0.09888 g N2
mass % N2 = (0.09888/0.138) * 100 %
= 71.654%
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