Question

Naturally occurring copper consists of copper 63 (62.9296 amu), and copper 65 (64.9278 amu). Using the relative atomic mass from the periodic table. which of the following is the best estimate of the percent abundance of the two isotopes of copper?

A) 50% copper 63 and 50% copper-65
B) 75% copper 63 and 25% copper 65
C) 25% copper 63 and 75% copper 65
D) 90% copper 63 and 10% copper 65
E) 10% copper 63 and 90% copper 65

Answer 1

Naturally occurring copper has two stable isotopes, copper-63 and copper-65, with an average atomic mass of 63.546 amu. Using the weighted average formula, the percent abundance is approximately 69% copper-63 and 31% copper-65, aligning with the standard atomic weight provided on the periodic table.

Step-by-step explanation:

Naturally occurring copper consists of two isotopes: copper-63 (63Cu) with a mass of 62.9296 atomic mass units (amu) and copper-65 (65Cu) with a mass of 64.9278 amu. The best estimate of the percent abundance of these two isotopes of copper can be found using the weighted average of their atomic masses, which is provided on the periodic table as 63.546 amu. To calculate the percent abundance of each isotope, we use the formula:

Weighted Average Formula:

Atomic Mass = (Mass of Isotope 1 × Percent Abundance of Isotope 1) + (Mass of Isotope 2 × Percent Abundance of Isotope 2)

By substituting the atomic masses and solving for the percent abundances, it has been determined that 63Cu has an abundance of approximately 69% and 65Cu has an abundance of approximately 31%. Therefore, the correct answer is as follows:

• 69% copper-63
• 31% copper-65

This aligns with the given standard atomic weight of copper, which is the average of these isotopes weighted by their natural abundance.