Concept explainers
An organic compound contains carbon (71.17%), hydrogen (5.12%) with the remainder nitrogen. Dissolving 0.177 g of the compound in 10.0 g of benzene gives a solution with a vapor pressure of 94.16 mm Hg at 25 °C. (The vapor pressure of pure benzene at this temperature is 95.26 mm Hg.) What is the molecular formula for the compound?
Interpretation Molecular formula of the compound has to be determined.
Concept introduction:
Raoult’s law: In a solution, vapor pressure of solvent is proportional to its mole fraction.
where,
Mole fraction: Amount of that component divided by the total amount of all of the components of the mixture
The number of moles of any substance can be determined using the equation
Answer to Problem 91IL
Molecular formula of the compound is
Explanation of Solution
Molecular formula of the compound is calculated.
Given,
Molar mass of carbon is
Molar mass of hydrogen is
Molar mass of nitrogen is
Vapour pressure of benzene at
Vapour pressure of pure benzene is
Mass of the compound is
Mass of benzene is
Molar mass of benzene is
The number of moles of any substance can be determined using the equation
Number of moles of benzene is
Vapour pressure of benzene is calculated by the given equation
Mole fraction of benzene is,
Hence,
Number of moles of the compound is
Hence,
The molar mass of compound is,
Number of moles of carbon is
Number of moles of hydrogen is
Empirical formula of the compound was determined.
Therefore,
The empirical formula of the compound is
Molecular mass of
The molar mass of a molecule is a simple multiple of the molar mass of its empirical formula. Hence,
Therefore,
Molecular formula of the compound is
Molecular formula of the compound is
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