Average Atomic Mass Quiz

What is the formula for calculating average atomic mass?

• Sum of (relative abundance × mass of isotope)

• Sum of (mass of isotope / fractional abundance)

• Sum of (mass of isotope × fractional abundance)

• Sum of (fractional abundance / mass of isotope)

If an element has naturally occurring isotopes with mass numbers of 63 and 65, and the relative abundances and atomic masses are 69.2% for a mass of 62.93 amu and 30.8% for a mass of 64.93 amu, what is the average atomic mass of the element?

• 63.55 amu

• 64.00 amu

• 63.00 amu

• 65.00 amu

Calculate the average atomic mass of sulfur if 95.00% of all sulfur atoms have a mass of 31.97 amu, 0.76% has a mass of 32.97 amu, and 4.22% have a mass of 33.97 amu.

• 32.07 amu

• 32.06 amu

• 32.08 amu

• 32.09 amu

Magnesium has three naturally occurring isotopes: magnesium-24 (78.99% abundance), magnesium-25 (10.00% abundance), and magnesium-26 (11.01% abundance). What is the element magnesium’s average atomic mass?

• 24.31 amu

• 25.00 amu

• 24.00 amu

• 26.00 amu

Suppose that sodium existed in two isotopes: sodium-22 and sodium-23. Which one would have the higher relative abundance and why?

• Sodium-23, because 23 is closer to the atomic mass of 22.99 of Na in the periodic table

• Sodium-22, because it is lighter.

• Sodium-23, because it has a higher mass.

• Sodium-22, because it is less stable.

Why is the average atomic mass of an element not a whole number?

• Because it is a weighted average of all isotopes.

• Because it is an arithmetic mean.

• Because it is a geometric mean.

• Because it is a simple average.

If an element has two isotopes with masses 10 amu and 11 amu, and their relative abundances are 20% and 80% respectively, what is the average atomic mass of the element?

• 10.80 amu

• 10.20 amu

• 11.00 amu

• 10.00 amu

What does the term "amu" stand for in atomic mass calculations?

• Atomic mass unit

• Atomic measurement unit

• Atomic molecular unit

• Atomic mass utility

If an element has three isotopes with masses 20 amu, 21 amu, and 22 amu, and their relative abundances are 90%, 5%, and 5% respectively, what is the average atomic mass of the element?

• 20.15 amu

• 21.00 amu

• 20.00 amu

• 22.00 amu

Which isotope of an element will contribute more to the average atomic mass?

• The isotope with the highest relative abundance.

• The isotope with the lowest relative abundance.

• The isotope with the highest mass.

• The isotope with the lowest mass.