Enriched weapons-grade uranium consists of 80% uranium-235 (235.044 amu) and 20% uranium-238 (238.051 amu). What is the average atomic mass of weapons-grade uranium, assuming the percentages are exact?

Question

Quizplus · Accepted Answer

To find the average atomic mass of weapons-grade uranium, we must use the weighted average formula:

Average atomic mass = (% abundance of U-235 x mass of U-235) + (% abundance of U-238 x mass of U-238)

Plugging in the given values, we get:

Average atomic mass = (0.80 x 235.044 amu) + (0.20 x 238.051 amu) 
= 188.0352 amu + 47.6102 amu 
= 235.6454 amu

Rounding off to the nearest hundredth gives us an answer of 235.65 amu, which is closest to choice D (235.645 amu).

Enriched Weapons-Grade Uranium Consists of 80% Uranium-235 (235