Chemistry for Engineering Students
Chemistry for Engineering Students
4th Edition
ISBN: 9781337398909
Author: Lawrence S. Brown, Tom Holme
Publisher: Cengage Learning
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Chapter 2, Problem 4CO
Interpretation Introduction

Interpretation:

Calculate the atomic weight of an element from the masses and abundances of its isotopes.

Concept Introduction:

Isotopes:

Atoms of same element have the same number of proton but different number of neutrons in its nucleus.

Ex: '1H, '2H,  '3H

These all are isotopes of H atom

Due to presence of different isotopes of an element we have to calculate average atomic mass, which is known as atomic weight of the element.

Expert Solution & Answer
Check Mark

Answer to Problem 4CO

Solution: Average atomic mass (atomic weight)

= f ' M1+f2 M2+f3 M3+...... fn Mn

f ': Fraction of M1 isotopes (fractional abundances)

M1: Atomic mass of first isotopes of the element

f2 : Fraction of M2 isotopes

M2: Atomic mass of second isotope of the element, and so on

Explanation of Solution

Due to isotopes of an element we cannot define atomic mass of the element. Each isotope is present in different amounts.

Hence we have to define average atomic mass.

Average atomic mass

=Total mass of elements No. of atoms

Let × atoms

  Fraction of M 1  is X 1 % Fraction of M 2  is X 2 % Fraction of  M 3  is X 3 %_ Fraction of  Mn is Xn%

Average atomic mass

=Total mass of element No. of atoms

=(M1X1)+(M2X2)+(M3X3)+(MnXn)(X1+X2+X3+...Xn)

=M1 ( X 1 X 1 + X 2 + X 3 +.... X n )+M 2  ( X 2 X 1 + X 2 + X 3 +.... X n )+Mn  ( X n X 1 + X 2 + X 3 +.... X n )

=M1f1+M2f2+....+Mnfn

Where  f 1 : abundance fraction of M 1    f 2 : abundance fraction of  M 2 _   f3: abundance fraction of M3

Hence average atomic mass (atomic weight)

= M1f1+M2f2+....+Mnfn

Where M1: Atomic mass of first isotopes

X1 : Abundance fraction of first isotopes

M2 : Atomic mass of second isotopes

X2:

Abundance fraction of second isotopes.

Conclusion

Average atomic mass (atomic weight)

= f ' M1+f2 M2+f3 M3+...... fn Mn

f ': Fraction of M1 isotope (fractional abundances)

M1: Atomic mass of first isotopes of the element

f2 : Fraction of M2 isotope

M2: Atomic mass of second isotope of the element and so on

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Chapter 2 Solutions

Chemistry for Engineering Students

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