Multiple Choice
An element has two isotopes, X and Y, with mass numbers of 52.0 and 53.0 respectively. The relative atomic mass is 52.2. What is the percentage abundance of isotope X?
2. Atoms & Elements
Isotopes
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Gallium has an atomic mass of 69.723 amu. The Ga-69 isotope (68.926 amu) is 60.11% abundant. What is the mass (amu) of the other isotope?
A
70.924 amu
B
71.926 amu
C
67.928 amu
D
69.723 amu
Verified step by step guidance1
Understand that the atomic mass of an element is the weighted average of the masses of its isotopes, based on their natural abundance.
Let the mass of the unknown isotope be represented as \( x \) amu. The abundance of Ga-69 is given as 60.11%, which means the abundance of the unknown isotope is \( 100\% - 60.11\% = 39.89\% \).
Set up the equation for the average atomic mass: \( 69.723 = (68.926 \times 0.6011) + (x \times 0.3989) \).
Solve the equation for \( x \) by first calculating the contribution of Ga-69 to the atomic mass: \( 68.926 \times 0.6011 \).
Subtract the contribution of Ga-69 from the atomic mass and divide by the abundance of the unknown isotope: \( x = \frac{69.723 - (68.926 \times 0.6011)}{0.3989} \).
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