A sample of chlorine weighing 20.57 grams contains two naturally occurring isotopes: Cl-35 and Cl-37. If the atomic masses are 34.9689 amu for Cl-35 and 36.9659 amu for Cl-37, and the natural abundance of Cl-35 is approximately 75.78%, what is the mass of Cl-35 in the sample?

• A. 4.98 grams
• B. 15.59 grams
• C. 10.29 grams
• D. 5.98 grams

Answer: (B)

Verified step by step guidance

1. Start by understanding that the sample of chlorine consists of two isotopes: Cl-35 and Cl-37. The problem provides the atomic masses and the natural abundance of Cl-35.
2. Calculate the mass of Cl-35 in the sample using its natural abundance. The natural abundance of Cl-35 is given as 75.78%, which means 75.78% of the total mass of the chlorine sample is Cl-35.
3. Convert the percentage of Cl-35 to a decimal by dividing by 100. This gives you 0.7578.
4. Multiply the total mass of the chlorine sample (20.57 grams) by the decimal form of the natural abundance of Cl-35 (0.7578) to find the mass of Cl-35 in the sample.
5. The equation for this calculation is: $20.57\times 0.7578$. Perform this multiplication to determine the mass of Cl-35 in the sample.