1.6 Relative atomic mass

• What is relative atomic mass (Ar)?

  Weighted average mass
• Steps to calculate the relative atomic mass (Ar) of carbon using its isotopes

  1️⃣ Multiply the percentage abundance by the mass of each isotope

  2️⃣ Sum the results

  3️⃣ Divide by 100 if using percentage abundance
• Relative atomic mass (Ar) is expressed relative to the mass of carbon-12
• What are isotopes?

  Atoms with same protons, different neutrons
• What is the formula to calculate relative atomic mass (Ar)?

  $Ar =$$\frac{\Sigma(\text{isotope mass} \times \text{percentage abundance})}{100}$
• How is the relative atomic mass of carbon calculated using its isotopes?

  (0.9889 × 12) + (0.0111 × 13)
• The relative atomic mass formula includes dividing by 100 to account for percentage abundance.


  True
• What is the calculated relative atomic mass of oxygen using its three isotopes (Oxygen-16, Oxygen-17, Oxygen-18)?

  15.9968
• The isotope mass used in calculating Ar is the mass number of each isotope
• The Ar of oxygen, rounded to the nearest whole number, is 16.

  True
• Stoichiometry relies on Ar to determine molar ratios
• Carbon-14 dating uses the ratio of carbon-14 to carbon-12 to determine sample age.

  True
• Match the carbon isotope with its properties:

  Carbon-12 ↔️ 98.89% abundance, mass 12

  Carbon-13 ↔️ 1.11% abundance, mass 13
• Carbon-12 and carbon-14 have the same number of protons but different numbers of neutrons.


  True
• What is the relative atomic mass of chlorine, calculated using its two isotopes?

  35.48
• The percentage abundance of an isotope is the proportion of that isotope in the element's natural occurrence
• The formula for calculating relative atomic mass is Ar = Σ(isotope mass × percentage abundance) / 100
• What does percentage abundance refer to in the context of isotopes?

  Proportion in natural occurrence
• What is the percentage abundance of Chlorine-35 in naturally occurring chlorine?

  75.77%
• The relative atomic mass of chlorine is approximately 35.48.


  True
• Relative atomic mass is defined as the weighted average mass of isotopes relative to carbon-12
• The relative atomic mass of chlorine is approximately 35.5 because of Cl-35 and Cl-37 isotopes.


  True
• Isotopes of the same element have the same mass number.

  False
• The relative atomic mass of chlorine is calculated to be 35.48
• What causes isotopes to have different mass numbers?

  Different number of neutrons
• Match the isotope with its mass and calculation for relative atomic mass (Ar) of chlorine:

  Chlorine-35 ↔️ Mass: 35, Calculation: (75.77/100) × 35

  Chlorine-37 ↔️ Mass: 37, Calculation: (24.23/100) × 37
• Steps to calculate the relative atomic mass (Ar) of oxygen using its three isotopes

  1️⃣ Multiply the percentage abundance by the mass of each isotope

  2️⃣ Sum the results

  3️⃣ Divide by 100 if using percentage abundance

  4️⃣ Round to the nearest whole number
• What does the acronym 'Ar' stand for in chemistry?

  Relative atomic mass
• What are the three isotopes of oxygen and their respective mass numbers?

  Oxygen-16, 17, 18
• How is the relative formula mass (Mr) of a compound calculated?

  Sum the Ar of elements
• What is one example of using Ar for element identification?

  Element with mass 23 is sodium
• What is the reference standard for calculating relative atomic mass?

  Carbon-12
• Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons
• What is the formula for calculating the relative atomic mass of an element?

  $\frac{\sum(\text{isotope mass} \times \text{percentage abundance})}{100}$
• Steps to calculate the relative atomic mass of chlorine

  1️⃣ Multiply the percentage abundance by the mass of each isotope

  2️⃣ Sum the results

  3️⃣ Divide by 100
• What two factors are needed to calculate the relative atomic mass (Ar) of an element?

  Isotope masses and abundances
• Isotope mass refers to the mass number of each isotope.


  True
• Chlorine has two naturally occurring isotopes: Chlorine-35 and Chlorine-37
• Steps to calculate the relative atomic mass (Ar) of chlorine

  1️⃣ Multiply the percentage abundance by the isotope mass for each isotope

  2️⃣ Sum the results

  3️⃣ The final sum is the relative atomic mass
• Match the application of relative atomic mass with its description:

  Calculating Relative Formula Mass (Mr) ↔️ Determining the Mr of compounds

  Stoichiometry ↔️ Calculating molar ratios in reactions

  Element Identification ↔️ Comparing experimental mass with standard Ar

  Isotope Dating ↔️ Using radioactive isotopes to age samples