Quantitative Chemical Analysis
Quantitative Chemical Analysis
9th Edition
ISBN: 9781464135385
Author: Daniel C. Harris
Publisher: W. H. Freeman
Question
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Chapter 18, Problem 18.CE

(a)

Interpretation Introduction

Interpretation:

For the given blue product, the value of molar absorptivity has to be calculated.

Concept introduction:

Beer-lambert law:

A=-logPPo=εcbwhere,A-absorbancePo-incidentirradianceandP-transmittedirradianceε-molarabsorptivityc-concentrationandb-pathlength.

(a)

Expert Solution
Check Mark

Answer to Problem 18.CE

The molar absorptivity (ε) value is 4.493×103M-1cm-1.

Explanation of Solution

Given information,

MassofNH4Clis1.00×10-2g.SampleAbsorbance(at625nm)Blank0.140Reference0.308Unknown0.592

Calculate the concentration of NH4Cl

1.00×10-2g53.491g/mol1.00L=1.869×10-4M.

Calculate the concentration of NH4Cl in the colored solution

(10mL50mL)(1.869×10-4M)=3.739×10-5M.

Apply the Beer’s law to calculate the value of molar absorptivity (ε)

ε=Abc=(0.308-0.140)(1.000)(3.739×10-5M)=4.493×103M-1cm-1.

The value of molar absorptivity (ε) is 4.493×103M-1cm-1.

(b)

Interpretation Introduction

Interpretation:

The weight percent of nitrogen in the protein sample has to be calculated.

(b)

Expert Solution
Check Mark

Answer to Problem 18.CE

The weight percent of nitrogen in the protein sample is 16.1%.

Explanation of Solution

Given information,

MassofNH4Clis1.00×10-2g.Concentrationofreferencesolutionis1.869×10-4M.massofproteinsampleis4.37mg.SampleAbsorbance(at625nm)Blank0.140Reference0.308Unknown0.592

Calculate the concentration of NH3 in the unknown solution

AbsorbanceofunknownAbsorbanceofreference=0.592-0.1400.308-0.140=ConcentrationofunknownConcentrationofreference(0.4520.168)(1.869×10-4)=5.028×10-4MNH3.

Calculate the mass of N in 100ml unknown solution

5.028×10-5molN×14.0067=0.7043mgofN.

Calculate the weight percent of nitrogen in the unknown solution

wt%ofN=100×(0.7043mg)4.37mg=16.1%.

The weight percent of nitrogen in the protein sample is 16.1%.

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