Relative atomic mass
2 marks · EasyA sample of element Y contains 75% of isotope ^{24}Y and 25% of isotope ^{25}Y. Calculate the relative atomic mass of Y. Give your answer to one decimal place.
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24.3 (±0.1)
Also accept: 24.3
Common mistakes: 24.25 (incorrect rounding)
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Marking points
M1 · 1 mark · Uses correct formula: (75 × 24 + 25 × 25)/100
A1 · 1 mark · Final answer correct to one decimal place: 24.3 (follow-through)
Worked solution
Relative atomic mass = (75 × 24 + 25 × 25) / 100 = (1800 + 625) / 100 = 2425 / 100 = 24.25.
To one decimal place: 24.3.