Question

an unknown element has these isotopes:

• a - 28: atomic mass = 27.98 amu, abundance = 92.23%

• a - 29: atomic mass = 28.98 amu, abundance = 4.67%

• a - 30: atomic mass = 29.97 amu, abundance = 3.10%

the average atomic mass of the element is: amu

Explanation:

Step1: Convert percentages to decimals

$92.23\% = 0.9223$, $4.67\%=0.0467$, $3.10\% = 0.031$

Step2: Calculate contribution of A - 28

$27.98\times0.9223=25.806954$

Step3: Calculate contribution of A - 29

$28.98\times0.0467 = 1.353366$

Step4: Calculate contribution of A - 30

$29.97\times0.031=0.92907$

Step5: Sum up contributions

$25.806954 + 1.353366+0.92907=28.08939$

Answer:

$28.09$