   Chapter 12, Problem 12.141QP General Chemistry - Standalone boo...

11th Edition
Steven D. Gammon + 7 others
ISBN: 9781305580343

Solutions

Chapter
Section General Chemistry - Standalone boo...

11th Edition
Steven D. Gammon + 7 others
ISBN: 9781305580343
Textbook Problem

A compound of carbon, hydrogen, and oxygen was burned in oxygen, and 1.000 g of the compound produced 1.434 g CO2 and 0.783 g H2O. In another experiment, 0.1107 g of the compound was dissolved in 25.0 g of water. This solution had a freezing point of −0.0894°C. What is the molecular formula of the compound?

Interpretation Introduction

Interpretation:

Given that 1.000 g of a compound containing Carbon, Hydrogen, Oxygen produced 1.434 g CO2 and 0.783 g H2O when burnt in oxygen. Freezing point of the solution of this compound is given.  Molecular formula of the compound has to be deduced.

Concept Introduction:

Depression in freezing point is a colligative property which refers to decrease in freezing point of the solution due to the addition of non-volatile solute. It is expressed as,

ΔTf = Kf.cm

Where,

ΔTf = depression in freezing pointKf = freezing point depression constantcm = molal concentration

Molality or molal concentration is one of the many parameters that is used to express concentration of a solution.  It is expressed as,

Molality = number of moles of solutemass of solvent in kg

Explanation

Given that mass of compound is 0.1107 g is dissolved in solvent water 25.0 g which is equivalent to 0.025 kg .

From the data given in the table 12.3 in text book, for water, Kf= 1.858°C/m

Freezing point of pure water is 0°C

Therefore, molality of the compound solution is,

ΔTf = Kf.cm

Rewriting the above equation,

cm  ΔTfKf Tf(solvent)-Tf(solution)20.0°C/m [0°C(-0.0894°C)]1.858°C/m = 0.04811 m

Moles of the compound are,

no. of moles = molality × mass of solvent = 0.04811 mol/kg × 0.025 kg 0.001203 mol

Molar mass of the compound is calculated as,

molar mass massno.of moles = 0.1107 g0.001203 mol = 92.02 g/mol

Given that 1.000 g of a compound containing Carbon, Hydrogen, Oxygen produced 1.434 CO2 and 0.783 H2O when burnt in oxygen. Calculate the empirical formula of compound using mass of C, O and H in 1.000 g of the compound

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