Relative atomic mass
3 marks · EasyThe table shows the isotopes of element Z and their percentage abundances:
| Isotope | Relative Mass | Percentage Abundance |
|---|---|---|
| Z-31 | 31 | 60 |
| Z-32 | 32 | 40 |
Calculate the relative atomic mass of Z. Give your answer to one decimal place.
Which isotope of Z is most abundant?
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) 31.4
(b) Z-31
Common mistakes: 32.4 (incorrect isotope abundance weighting)
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Uses correct formula to multiply each mass by abundance, sum, divide by 100.
A1 (a) · 1 mark · Final answer correct to one decimal place: 31.4. (follow-through)
B1 (b) · 1 mark · Correct identification of most abundant isotope: Z-31.
Worked solution
a) Relative atomic mass = (60 × 31 + 40 × 32)/100 = (1860 + 1280)/100 = 3140/100 = 31.4
b) Z-31 is the most abundant isotope as it has the highest percentage abundance (60%).