Question

An unknown element X has the following isotopes: ²⁵X (80.5% abundant) and ²⁷X (19.5% abundant). What is the average atomic mass in amu of X?

Answer 1

Answer:

25.4 amu

Explanation:

Step 1: Given data

• Mass of the isotope ²⁵X (m²⁵X): 25 amu

• Abundance of the isotope ²⁵X (ab²⁵X): 80.5 % = 0.805

• Mass of the isotope ²⁷X (m²⁷X): 27 amu

• Abundance of the isotope ²⁷X (ab²⁷X): 19.5% = 0.195

Step 2: Calculate the average atomic mass of X

We will use the following expression.

m = m²⁵X × ab²⁵X + m²⁷X × ab²⁷X

m = 25 amu × 0.805 + 27 amu × 0.195

m = 25.4 amu