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Ans. Relative atomic mass is a measure of the average mass of atoms of an element compared to the mass of a standard atom, usually carbon-12 (12C). It is expressed as a ratio with no units.
Q. 2 : What is an Atomic Mass Unit (amu or u)?
Ans. An atomic mass unit (amu or u) is a unit of mass used to express atomic and molecular masses. One atomic mass unit is defined as one-twelfth of the mass of a carbon-12 (12C) atom.
Q. 3 : What is Average Atomic Mass?
Ans. Average atomic mass is the weighted average of the masses of all naturally occurring isotopes of an element, considering their relative abundances in nature.
Q. 4 : What is Relative Molecular Mass?
Ans. Relative molecular mass is the ratio of the average mass of a molecule to one-twelfth of the mass of a carbon-12 (12C) atom. It is expressed as a ratio with no units.
Q.5 : How are these Concepts Applied in Chemistry?
Ans. These concepts are applied in various aspects of chemistry, including stoichiometry calculations, determining molar masses, and understanding the composition of substances in chemical reactions.
Relative Atomic Mass, Atomic Mass Unit, Average Atomic Mass And Relative Molecular Mass
Relative Atomic Mass : Relative atomic mass, also known as atomic weight, is the weighted average mass of an element's atoms compared to 1/12th the mass of a carbon-12 atom. It accounts for the presence of different isotopes and their abundances, providing a precise measurement for chemical calculations.
Shrivastav 25 Jun, 2024
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Relative Atomic Mass :
Chemistry is an enchanting journey into the world of matter, where we unravel the mysteries of atoms and molecules. Central to this exploration are concepts like relative atomic mass, atomic mass unit (amu or u), average atomic mass, and relative molecular mass. Let's demystify these concepts in simple terms.
Relative Atomic Mass : Understanding the Mass of Atoms
What is Relative Atomic Mass?
Relative atomic mass is a measure of the average mass of atoms of an element compared to the mass of a standard atom, which is usually taken as carbon-12 (
12
C). It is a dimensionless quantity and is often expressed as a ratio with no units.
Relative Atomic mass is defined as the number which indicates how many times the mass of one atom of an element is heavier in comparison to 1/12
th
part of the mass of one atom of C-12.
Why is Relative Atomic Mass Important?
Relative atomic mass helps us understand the mass of atoms relative to one another. It provides insights into the abundance of isotopes of an element and their contributions to the overall mass of the element.
Atomic Mass Unit (amu or u) : Standard Unit of Atomic Mass
What is an Atomic Mass Unit (amu or u)?
An atomic mass unit (amu or u) is a unit of mass used to express atomic and molecular masses.
The quantity 1/12
th
mass of an atom of C
12
is known as atomic mass unit.
Since mass of 1 atom of C-12 = 1.992648 × 10
–23
g
I
t may be noted that the atomic masses as obtained above are the relative atomic masses and not the actual masses of the atoms. These masses on the atomic mass scale are expressed in terms of atomic mass units (abbreviated as amu). Today’s ‘amu’ has been replaced by ‘u’ which is known as
unified amu
.
Ex.
The atomic mass of an element is 50
Calculate the mass of one atom, in amu
Calculate the mass of 6.022 × 10
23
atoms, in gm
Calculate the number of atoms in its 10 gm
What mass of the element contains 3.011 × 10
20
atoms
Sol.
(i) 50 amu
(ii) 50 gm
(iii)
∵
50 gm of element contains 6.022 × 10
23
atoms
(iv)
∵
6.022 × 10
23
atoms weights 50 gm
Why is the Atomic Mass Unit Important?
The atomic mass unit provides a standardized way to express the masses of atoms and molecules. It allows us to compare the masses of different atoms and molecules on a consistent scale.
Average Atomic Mass : Combining Isotopic Masses
What is Average Atomic Mass?
Average atomic mass is the weighted average of the masses of all naturally occurring isotopes of an element, taking into account their relative abundances in nature.
If an element exists in different isotopic forms having relative abundance, X
1
%, X
2
% … X
n
%, with relative atomic masses M
1
, M
2
… M
n
respectively then
Q.
Ex.
An element exist in nature in two isotopic forms: X
30
(90%) and X
32
(10%). What is the average atomic mass of element?
Why is Average Atomic Mass Significant?
Average atomic mass provides a representative value for the mass of an element, considering the contributions of its various isotopes. It is useful for calculating stoichiometry in chemical reactions and determining the molar mass of elements.
Relative Molecular Mass : The Mass of Molecules
What is Relative Molecular Mass?
The number which indicates how many times the mass of one molecule of a substance is heavier in comparison to 1/12
th
part of the mass of an atom of C-12.
OR
The molecular mass of a substance is the sum of atomic masses of all the atoms present in a molecule. It is obtained by multiplying the atomic mass of each element by the number of its atoms and adding them together.
Ex.
Molecule mass of oxygen (O
2
) = 32
Molecular mass of (O
3
) = 48
Molecular mass of HCl = 1 + 35.5 = 36.5
Molecular mass of H
2
SO
4
= 2 + 32 + 64 = 98
Why is Relative Molecular Mass Important?
Relative molecular mass helps us understand the mass of molecules relative to one another. It provides insights into the composition and properties of substances, guiding scientific inquiry and experimentation.
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