Question

The mass spectrum of a hypothetical element shows that 78.21% of the atoms have a mass of 27.977 u, 1.346% have a mass of 28.976 u, and the remaining have a mass of 29.974 u. Calculate the average atomic mass of this element (in units of u). (Use 4 Sig. Fig. Don't round until end.)

Answer 1

Answer: 28.40

Explanation:

For A(27.977 u)

Mass number = 27.977

Abundance = 78.21%

For B (28.976 u)

Mass number = 28.976

Abundance = 1.346%

For C(29.974 u)

Mass number = 29.974

Abundance = 20.444%

Averages atomic mass

= (Mass of A x abundance of A)/100 + (Mass of B x abundance of B)/100 + (Mass of C x abundance of C)/100

= (27.977x78.21)/100 + (28.976x1.346)/100 + (29.974x20.444)/100

= 21.8808117 + 0.39001696 + 6.12788456

= 28.40