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General Chemistry - Standalone boo...

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

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BuyFindarrow_forward

General Chemistry - Standalone boo...

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

Analysis of a compound gave 39.50% C, 2.21% H, and 58.30% Cl. When 0.855 g of this solid was dissolved in 7.50 g of naphthalene, the solution had a freezing point of 78.0°C. The pure solvent freezes at 80.0°C; its molal freezing point constant is 6.8°C/m.

  1. a What is the molecular formula of the compound?
  2. b What is its molecular weight to the nearest 0.1 g?

(a)

Interpretation Introduction

Interpretation:

A compound contains 39.50% Carbon , 2.21% Hydrogen and 58.30% Chlorine. 0.855 g of this substance is dissolved in 7.50 g of naphthalene and the solution has freezing point of 78°C. Molecular formula of the compound has to be determined.

Concept Introduction:

Depression in freezing point is the phenomenon of lowering of freezing point of a substance, which is considered as solvent, by adding a non-volatile solute.   It is expresses as –

ΔTf = Kf × m

Where,

ΔTf = depression in freezing pointKf  = cryoscopic constantm    = molality of the solute

Number of moles of a substance is related to molar mass of the substance as,

no.of moles massmolar mass

Explanation

Given that freezing point of the solution is 78°C. freezing point of pure naphthalene is 80°C . Kf for naphthalene is 6.8°C/m. rewriting the depression in freezing point equation, determine the molality of the solution.

m = ΔTfKf = [80°C78°C)]6.8°C/m = 0.294 m

Number of moles of the compound considering 1 kg of solvent,

moles = 0.294 mol1 kg of solvent×0.00750 kg = 2.21×103 mol

Molar mass of the compound is calculated as,

molar mass =  0.855 g2.21×103 mol = 387 g/mol

Number of moles of elements in 100 g of the compound are calculated as follows -

moles of C = 39

(b)

Interpretation Introduction

Interpretation:

A compound contains 39.50% Carbon , 2.21% Hydrogen and 58.30% Chlorine. 0.855 g of this substance is dissolved in 7.50 g of naphthalene and the solution has freezing point of 78°C. Molar mass of the compound nearest to the tenth of a gram has to be determined.

Concept Introduction:

Depression in freezing point is the phenomenon of lowering of freezing point of a substance, which is considered as solvent, by adding a non-volatile solute.   It is expresses as –

ΔTf = Kf × m

Where,

ΔTf = depression in freezing pointKf  = cryoscopic constantm    = molality of the solute

Number of moles of a substance is related to molar mass of the substance as,

no.of moles massmolar mass

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Chapter 12 Solutions

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Sect-12.4 P-12.7ESect-12.4 P-12.8ESect-12.4 P-12.9ESect-12.4 P-12.10ESect-12.4 P-12.11ESect-12.5 P-12.12ESect-12.5 P-12.5CCSect-12.6 P-12.13ESect-12.6 P-12.14ESect-12.6 P-12.15ESect-12.7 P-12.16ESect-12.7 P-12.6CCSect-12.8 P-12.17ESect-12.8 P-12.7CCSect-12.9 P-12.18ESect-12.9 P-12.8CCCh-12 P-12.1QPCh-12 P-12.2QPCh-12 P-12.3QPCh-12 P-12.4QPCh-12 P-12.5QPCh-12 P-12.6QPCh-12 P-12.7QPCh-12 P-12.8QPCh-12 P-12.9QPCh-12 P-12.10QPCh-12 P-12.11QPCh-12 P-12.12QPCh-12 P-12.13QPCh-12 P-12.14QPCh-12 P-12.15QPCh-12 P-12.16QPCh-12 P-12.17QPCh-12 P-12.18QPCh-12 P-12.19QPCh-12 P-12.20QPCh-12 P-12.21QPCh-12 P-12.22QPCh-12 P-12.23QPCh-12 P-12.24QPCh-12 P-12.25QPCh-12 P-12.26QPCh-12 P-12.27QPCh-12 P-12.28QPCh-12 P-12.29QPCh-12 P-12.30QPCh-12 P-12.31QPCh-12 P-12.32QPCh-12 P-12.33QPCh-12 P-12.34QPCh-12 P-12.35QPCh-12 P-12.36QPCh-12 P-12.37QPCh-12 P-12.38QPCh-12 P-12.39QPCh-12 P-12.40QPCh-12 P-12.41QPCh-12 P-12.42QPCh-12 P-12.43QPCh-12 P-12.44QPCh-12 P-12.45QPCh-12 P-12.46QPCh-12 P-12.47QPCh-12 P-12.48QPCh-12 P-12.49QPCh-12 P-12.50QPCh-12 P-12.51QPCh-12 P-12.52QPCh-12 P-12.53QPCh-12 P-12.54QPCh-12 P-12.55QPCh-12 P-12.56QPCh-12 P-12.57QPCh-12 P-12.58QPCh-12 P-12.59QPCh-12 P-12.60QPCh-12 P-12.61QPCh-12 P-12.62QPCh-12 P-12.63QPCh-12 P-12.64QPCh-12 P-12.65QPCh-12 P-12.66QPCh-12 P-12.67QPCh-12 P-12.68QPCh-12 P-12.69QPCh-12 P-12.70QPCh-12 P-12.71QPCh-12 P-12.72QPCh-12 P-12.73QPCh-12 P-12.74QPCh-12 P-12.75QPCh-12 P-12.76QPCh-12 P-12.77QPCh-12 P-12.78QPCh-12 P-12.79QPCh-12 P-12.80QPCh-12 P-12.81QPCh-12 P-12.82QPCh-12 P-12.83QPCh-12 P-12.84QPCh-12 P-12.85QPCh-12 P-12.86QPCh-12 P-12.87QPCh-12 P-12.88QPCh-12 P-12.89QPCh-12 P-12.90QPCh-12 P-12.91QPCh-12 P-12.92QPCh-12 P-12.93QPCh-12 P-12.94QPCh-12 P-12.95QPCh-12 P-12.96QPCh-12 P-12.97QPCh-12 P-12.98QPCh-12 P-12.99QPCh-12 P-12.100QPCh-12 P-12.101QPCh-12 P-12.102QPCh-12 P-12.103QPCh-12 P-12.104QPCh-12 P-12.105QPCh-12 P-12.106QPCh-12 P-12.107QPCh-12 P-12.108QPCh-12 P-12.109QPCh-12 P-12.110QPCh-12 P-12.111QPCh-12 P-12.112QPCh-12 P-12.113QPCh-12 P-12.114QPCh-12 P-12.115QPCh-12 P-12.116QPCh-12 P-12.117QPCh-12 P-12.118QPCh-12 P-12.119QPCh-12 P-12.120QPCh-12 P-12.121QPCh-12 P-12.122QPCh-12 P-12.123QPCh-12 P-12.124QPCh-12 P-12.125QPCh-12 P-12.126QPCh-12 P-12.127QPCh-12 P-12.128QPCh-12 P-12.129QPCh-12 P-12.130QPCh-12 P-12.131QPCh-12 P-12.132QPCh-12 P-12.133QPCh-12 P-12.134QPCh-12 P-12.135QPCh-12 P-12.136QPCh-12 P-12.137QPCh-12 P-12.138QPCh-12 P-12.139QPCh-12 P-12.140QPCh-12 P-12.141QPCh-12 P-12.142QP

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