Practice Problem: Isotopic Abundance and Atomic Mass

Professor Dave explains how to calculate the average atomic mass of silicon using isotopic abundances. He provides the percentages of silicon isotopes and demonstrates the calculation process by multiplying each isotope's mass number by its abundance. The tutorial emphasizes the importance of significant figures in the final result, which is 28.1 atomic mass units. The video also suggests reviewing related tutorials on nuclide symbols and isotopes for better understanding.

What percentage of silicon atoms in the universe are Silicon-28?

• 3.10%

• 28.1%

• 92.23%

• 4.67%

How do you calculate the average atomic mass of an element?

• Add the mass numbers of all isotopes

• Multiply the mass number of each isotope by its abundance and sum them

• Subtract the smallest mass number from the largest

• Divide the total mass by the number of isotopes

What is the mass number of Silicon-29?

• 31

• 30

• 28

• 29

Why should the final answer for the average atomic mass have three significant figures?

• Because the values used in the calculation have varying significant figures, limiting the answer to the least number

• Because the calculated average is always rounded to three significant figures

• Because the percentages have three significant figures

• Because the mass numbers have three significant figures

What is the average atomic mass of silicon as found on the periodic table?

• 30.0

• 28.1

• 28.0

• 29.0