Average Atomic Mass!!!. Copper is made of two isotopes. Copper- 63 is 69.17% abundant and it has a mass of 62.9296 amu. Copper-65 is 30.83% abundant and.

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Presentation transcript:

Average Atomic Mass!!!

Copper is made of two isotopes. Copper- 63 is 69.17% abundant and it has a mass of amu. Copper-65 is 30.83% abundant and it has a mass of amu. What is the weighted average mass of these two isotopes?

Calculate the atomic mass of silicon. The three silicon isotopes have atomic masses and relative abundances of amu ( %), amu (4.6832%) and amu (3.0872%).

If you know the element, look up the atomic mass on the periodic table. It's the number with places after the decimal. If there are only two isotopes they have to add up to 100% (or in decimal form 1) so you set it up like this: (atomic weight of one isotope)(x) + (atomic weight of other isotope)(1-x) = the atomic mass you find on the table. Use algebra to find x. Don't forget to use the distributive property.

Example: Cl-35 weighs amu Cl-37 weighs amu (34.969)(x) + (36.966)(1-x) = (on the table for Chlorine) x x = x = x = So…. Cl-35 abundance is % and Cl-37 is %

Antimony has two naturally occurring isotopes. The mass of antimony-121 is amu and the mass of antimony-123 is amu. Using the average mass from the periodic table, find the abundance of each isotope. (Remember that the sum of the two abundances must be 100).

ANSWER 57.2% Sb % Sb-123