###### Asked in PhysicsChemistryElements and Compounds

Physics

Chemistry

Elements and Compounds

# How do you use the mass and percent abundance to calculate mass number?

## Answer

###### Wiki User

###### September 03, 2008 1:15AM

chlorine - 35

## Related Questions

###### Asked in Atomic Mass

### How do you calculate the atomic mass of an element with different isotopes?

To calculate average atomic mass from different isotopes of an
element, we take into account the relative atomic masses of
isotopes and their relative abundance on Earth. The following
formula is used to calculate the needful :
atomic mass = mass of isotope x percent abundance + mass of
isotope x percent abundance / 100 (whole expression divided by
100)

###### Asked in Periodic Table, Atoms and Atomic Structure

### The mass number of an atom is the sum of its?

The mass number of an atom is the average of all it's isotopes
in ratio to how often an isotope occurs naturally (abundance). An
isotope is a variant of an element that has a different number of
neutrons, therefore causing the atom to have a different mass. The
percent abundance of an isotope is converted to a fraction, and
multiplied by the mass of the isotope. Then all the factional
masses of different isotopes are added together.
Atomic mass = (mass isotope 1)x(fractional natural abundance of
isotope 1) + (mass isotope 2)x(fractional natural abundance of
isotope 2) + (mass isotope 3)x(fractional natural abundance of
isotope 3)
For example:
Hydrogen has 3 naturally occurring isotopes:
Protium - Abundance - 99.985% (.99985) Mass - 1.0078
Deuterium - Abundance - .015% (.00015) Mass - 2.014
Tritium - Abundance - 0% (.000) Mass - 3.016
Atomic mass number of Hyrdogen = (.99985)(1.0078) +
(.00015)(2.014) + (.000)(3.016) = 1.00795
Go look up the mass number of Hydrogen on the periodic table and
it says 1.008

###### Asked in Atomic Mass

### Isotopes to calculate atomic mass for zinc?

I have the five isotopes of zinc, each with its percent by mass
abundance and the compostition of its nucleus. Now I need to
calculate the approximate atomic mass of zinc as I would find it in
nature and listed on the periodic table. How do I go about doing
this? in the first isotope there are 30p and 34n and the percent
mass abundance is 48.89% the second isotope is 30p and 36n and
27.81% third isotope is 30p and 37n 4.11% fourth isotope is 30p and
38n and 18.57% and the fifth isotope has 30p and 40n and 0.62%.
Any help anyone can provide I would greatly appreciate!
THANKS
4 years ago
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DavidB
Best Answer - Chosen by
Voters
For each isotope calculate the mass number (# protons + # neutrons)
for each atom. This is its approximate atomic mas. Then calculate
the average mass for all the isotopes. Covert the percentages to
decimals then multiply each mass number by the decimal of the
abundance and add all the terms
(64 x 0.4889) + (mass # 2 + 0.2781) + (......) + (......) + (
.....)
4 years ago

###### Asked in Chemistry, DIY Projects

### How do you calculate percent abundance for antimony?

The atomic mass of an element is the weighted average of the
masses of its isotopes. You know that: Antimony-121 has a mass of
120.9038 u, x% abundance Antimony-123 has a mass of 122.9042 u, y%
abundance There are only 2 isotopes for antimony and their percent
abundances should add up to 100%. In other words: x% + y% = 100% y
= 1-x (percentages written as decimals) So, now let's put
everything together. In order to calculate the atomic mass,
multiply the percent abundance of an isotope by its atomic mass;
then add the product of all the isotopes: (Atomic Mass of
Antimony-121)(Percent Abundance of Antimony-121) + (Atomic Mass of
Antimony-123)(Percent Abundance of Antimony-123) = Atomic Mass of
Element Antimony (120.9038 amu)(x) + (122.9042 amu)(y) = 121.760
amu Replacing 1-x for y gives: (120.9038 amu)(x) + (122.9042
amu)(1-x) = 121.760 amu Solve for x: 120.9038x + 122.9042
-122.9042x = 121.760 amu -2.0040x = -1.1442 x = 0.57096 = 57.096%
Solve for y: y = 1 - x y = 1 - 0.57096 = 0.42904 = 42.904%

###### Asked in Atomic Mass

### How do you calculate the average relative atomic mass of neon?

To calculate the relative atomic mass of an element (which is by
its definition an average), you need the mass number and relative
abundance of each isotope present.
Suppose we have the following data from the mass
spectrometer:
first isotope mn X, abundance A%
second isotope mn Y, abundance B%
third isotope mn Z, abundance C%.
Then ram = (A/100 x X) + (B/100 x Y) + (C/100 x Z)
If there are more than 3 isotopes, just do the same for each one
and add all the expressions together.