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Question
The three stable isotopes of neon: `""_10^20"Ne"`, `""_10^21"Ne"` and `""_10^22"Ne"` have respective abundances of 90.51%, 0.27% and 9.22%. The atomic masses of the three isotopes are 19.99 u, 20.99 u and 21.99 u, respectively. Obtain the average atomic mass of neon.
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Solution
Atomic mass of `""_10^20"Ne"`, m1 = 19.99 u
Abundance of `""_10^20"Ne"`, η1 = 90.51%
Atomic mass of `""_10^21"Ne"`, m2 = 20.99 u
Abundance of `""_10^21"Ne"`, η2 = 0.27%
Atomic mass of `""_10^22"Ne"`, m3 = 21.99 u
Abundance of `""_10^22"Ne"`, η3 = 9.22%
The average atomic mass of neon is given as:
`"m" = ("m"_1η_1 + "m"_2η_2 + "m"_3η_3)/(η_1 + η_2 + η_3)`
= `(19.99 xx 90.51 + 20.99 xx 0.27 + 21.99 xx 9.22)/(90.51 + 0.27 + 9.22)`
= 20.1771 u
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