   # The nitrogen content of organic compounds can be determined by the Dumas method. The compound in question is first reacted by passage over hot CuO( s ): Compound → CuO( s ) Hot N 2 ( g ) + CO 2 ( g ) + H 2 O ( g ) The product gas is then passed through a concentrated solution of KOH to remove the CO 2 . After passage through the KOH solution, the gas contains N 2 and is saturated with water vapor. In a given experiment a 0.253-g sample of a compound produced 31.8 mL N 2 saturated with water vapor at 25°C and 726 torr. What is the mass percent of nitrogen in the compound? (The vapor pressure of water at 25°C is 23.8 torr.) ### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243

#### Solutions

Chapter
Section ### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243
Chapter 8, Problem 129AE
Textbook Problem
107 views

## The nitrogen content of organic compounds can be determined by the Dumas method. The compound in question is first reacted by passage over hot CuO(s): Compound  → CuO( s ) Hot  N 2 ( g )   +  CO 2 ( g )   +  H 2 O ( g ) The product gas is then passed through a concentrated solution of KOH to remove the CO2. After passage through the KOH solution, the gas contains N2 and is saturated with water vapor. In a given experiment a 0.253-g sample of a compound produced 31.8 mL N2 saturated with water vapor at 25°C and 726 torr. What is the mass percent of nitrogen in the compound? (The vapor pressure of water at 25°C is 23.8 torr.)

Interpretation Introduction

Interpretation: The mass percentage of nitrogen in the given compound to be determined if the 0.253g of compound sample is producing 31.8mL N2 with water vapor at 25oC and 726torr .

Concept introduction:

• Partial pressure of a gas in a mixture of gases is the pressure of that gas when it alone.
• Total pressure of a flask containing mixture of gases is the sum of individual partial pressures of constituted gases.
• Number of moles of a substance, According to ideal gas equation,

Numberofmoles=Pressure×VolumeR×Temperature

• Number of grams of a substance from its number of moles is,

Number of moles×Molecularmass in grams=Numberofgrams

• Mass percentage of a substance in a compound sample undergoing reaction is the ratio of mass of substance produced to the mass of compound sample taken and multiplied with 100.

### Explanation of Solution

Explanation

• To find: the Partial pressure of produced N2 in the given reaction.

The Partial pressure of N2 in the given reaction is 702torr .

The total pressure is given as 726torr .

The partial pressure of water in the given reaction is given as 23.8torr .

The total pressure of sample contains partial pressure of N2 and water.

Therefore,

The Partial pressure of N2 in the sample is,

726torr-23.8torr=702torr

• To find: the number of moles of produced N2 gas in the given reaction.

The number of moles of produced N2 gas is 1.20×10-3mol .

The Partial pressure of N2 is calculated as 702torr=702torr×1atm760torr=0.924atm .

The volume of N2 gas is given as 31.8mL=31.8mL×1L1000mL=0.0318L .

The temperature of N2 gas is given as 25oC=(25+273)K=298K .

The equation for finding number of moles of a substance,

According to ideal gas equation,

Numberofmoles=Pressure×VolumeR×Temperature

Therefore,

The number of moles of N2 gas is,

Numberofmoles=0

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