Question

An element is said to be enriched with respect to a particular isotope if it has an unnaturally large abundance of that isotope. Consider a sample of Cl2 that is enriched with 35CI 35C1 mass = 34.97 amu abundance = 85.00 % 37C1 mass = 36.97 amu abundance = 15.00 % (a) Calculate the atomic weight of the enriched Cl (b) How many Cl2 molecules are in a 0.345 g sample of the enriched chlorine?

Answer 1

(a) Atomic Mass = 35.24

(b) 2.95x10²¹ Cl₂ molecules

Step-by-step explanation:

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(a) We calculate the atomic weight of the enriched Cl using the abundances and masses of the isotopes:

• Atomic Mass = 34.97 * 0.85 + 36.79 * 0.15

• Atomic Mass = 35.24 amu

(b) We use the previously calculated atomic mass and use it as molar mass (35.24 g/mol), alongside Avogadro's number:

• Molar mass of Cl₂ = 35.24 * 2 = 70.48 g/mol

• 0.345 g ÷ 70.48 g/mol = 4.90x10⁻³ mol Cl₂

• 4.90x10⁻³ mol Cl₂ * 6.023x10²³ molecules/mol = 2.95x10²¹ Cl₂ molecules