# Worksheet: Relative Atomic Mass

In this worksheet, we will practice calculating the relative isotopic abundance of elements and using these data to calculate their relative atomic masses.

Q1:

The atomic mass unit (u) is defined as th of the mass of an atom of carbon-12. What is the mass of a carbon-13 atom in atomic mass units, to 2 significant figures?

Q2:

The atomic mass unit (u) is defined as th of the mass of an atom of carbon-12. What is the mass of a silicon-30 atom in atomic mass units?

Q3:

The atomic mass unit (u) is defined as th of the mass of an atom of carbon-12. What is the mass of a fluorine-19 atom in atomic mass units?

Q4:

The relative atomic mass of an element is the average mass of one atom on a scale .

• Awhere the most common isotope of the element has a mass of 100
• Bfrom 0–100, where 0 is the mass of hydrogen and 100 is the mass of the heaviest element
• Cwhere hydrogen-1 has a mass of 1
• Dwhere carbon-12 has a mass of 12

Q5:

Relative isotopic mass is the mass of an isotope of an element on a scale .

• Awhere the most common isotope of the element has a mass of 100
• Bwhere carbon-12 has a mass of 12
• Cfrom 0–100, where 0 is the mass of hydrogen and 100 is the mass of the heaviest element
• Dwhere hydrogen-1 has a mass of 1

Q6:

As a molar percentage, 80.3% of a boron sample is and the remainder is . What is the average molar mass of the boron sample?

Q7:

Chlorine has two stable isotopes, chlorine-35 and chlorine-37. A sample of chlorine was analyzed using a mass spectrometer, and the following isotopic abundances were calculated.

Isotope Abundance (mol %) Chlorine-35 Chlorine-37 75.8% 24.2%

What is the relative atomic mass of chlorine in the sample?