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The average atomic mass of a sample of an element X is 16.2 u.... - Science
Question
The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes ^{16}_{8}\text{X} and ^{18}_{8}\text{X} in the sample?
Answer
Let the percentage of isotope ^{16}_{8}\text{X} be x\%.
Then, the percentage of isotope ^{18}_{8}\text{X} will be (100 - x)\%.
Average atomic mass = 16.2 u
Formula:
16.2 = (16 \times \frac{x}{100}) + (18 \times \frac{100 - x}{100})
16.2 = \frac{16x + 1800 - 18x}{100}
16.2 \times 100 = 1800 - 2x
1620 = 1800 - 2x
2x = 1800 - 1620
2x = 180
x = 90
Therefore:
Percentage of
^{16}_{8}\text{X}= 90%Percentage of
^{18}_{8}\text{X}=100 - 90 =10%