Average Atomic Mass

What is average atomic mass?

• The average atomic mass is the sum of all isotopes' masses.
• Weighted average of the masses of the existing isotopes of an element.

• The average atomic mass is the mass of the most abundant isotope.
• The average atomic mass is a fixed value for all elements.

What is the unit for average atomic mass?

• grams (g)
• moles (mol)
• atomic mass units (amu)
• kilograms (kg)

Place the label in the correct value.

a

b

c

d

Copper-65's mass

Copper-63's mass

Copper-63's Percent abundance

Copper-65's Percent abundance

Strontium-84 with 0.50%

Strontium-86 with 9.9%

Strontium-87 with 7.0%

Strontium-88 with 82.6%

Match the mass with the correct percentage

• 0.07

• 86

• 0.099

• 88

• 0.005

• 87

• 0.826

• 84

Order the following steps in the correct order:

• Find the contribution of each isotope

• Add the relative abundances from each isotope together.

• Round answer to two numbers after the decimal

What number must all percent abundances add up to?

Titanium (Ti) has five common isotopes: 8.0% is Titanium 46, 7.8% is Titanium 47, 73.4% is Titanium 48, 5.5% is Titanium 49, and the rest is Titanium 50.

What is titanium 50's percent abundance?

• 4.5%
• 6.0%
• 7.2%
• 5.3%

Element X has two isotopes. One has a mass of 10.0 amu and an abundance of 20.0%. The other has a mass of 11.0 amu and an abundance of 80.0%. What is the average atomic mass?

Mathematical Equivalence

ON

Element J has two isotopes. J-35 has an abundance of 75.78%; and J-37 has an abundance of 24.22%. What is the average atomic mass of this element?

Mathematical Equivalence

ON

An isotope has three forms.  30% have a mass of 4 amu, 20% have a mass of 5 amu and 50% have a mass of 3 amu.  Average atomic mass will be closest to

• 2 amu
• 3 amu
• 4 amu
• 5 amu