average atomic mass how to use relative abundance to calculate average atomic mass
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Average Atomic MassHow to use relative abundance to
calculate average atomic mass
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Relative Abundance
• The percent of each elements Isotopes that are present in the world.
• Rubidium is a soft, silvery-white metal that has two common isotopes, 85Rb and 87Rb. If the abundance of 85Rb is 72.2% and the abundance of 87Rb is 27.8%
Relative Abundance
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Calculating Average Atomic Mass
1. Take the percent of relative abundance and convert into a decimal by moving the decimal two places to the left.
2. Multiply the new decimal by the mass that it goes with
3. Record your number4. Complete steps 1-3 for all of the isotopes present
in the problem5. Once you have a value for all isotopes add them
together.
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Examples
• Rubidium is a soft, silvery-white metal that has two common isotopes, 85Rb and 87Rb. If the abundance of 85Rb is 72.2% and the abundance of 87Rb is 27.8%, what is the average atomic mass of rubidium?
• Uranium is used in nuclear reactors and is a rare element on earth. Uranium has three common isotopes. If the abundance of 234U is 0.01%, the abundance of 235U is 0.71%, and the abundance of 238U is 99.28%, what is the average atomic mass of uranium?
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• Titanium has five common isotopes: 46Ti (8.0%), 47Ti (7.8%), 48Ti (73.4%), 49Ti (5.5%), 50 Ti (5.3%). What is the average atomic mass of titanium?
Naturally occurring chlorine that is put in pools is 75.53 percent 35Cl and 24.47 percent 37Cl Calculate the average atomic mass.
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Copper used in electric wires comes in two flavors (isotopes): 63Cu and 65Cu. 63Cu has an atomic mass of amu and an abundance of 69.09%. The other isotope, 65Cu, has an abundance of 30.91%. Calculate the average atomic mass
Magnesium consists of three naturally occurring isotopes. The percent abundance of these isotopes is as follows: 24Mg (78.70%), 25Mg (10.13%), and 26Mg (11.7%).