Relative atomic mass

2 marks · Hard

A sample of element Q contains 10% of isotope Q-40 and 90% of isotope Q-42.

Calculate the relative atomic mass of Q. Give your answer to one decimal place.

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Show answer

41.8 (±0.1)

Also accept: 41.8 u

Common mistakes: Arithmetic slip in calculation; Incorrect abundance applied

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Marking points

M1 · 1 mark · Correct method: (40 × 10) + (42 × 90) divided by 100.

A1 · 1 mark · Correct answer obtained: 41.8 (accept answer to 1 decimal place). (follow-through)

Worked solution

Relative atomic mass = (percentage of Q-40 × mass of Q-40) + (percentage of Q-42 × mass of Q-42) divided by 100:

= (400 + 3780) / 100

= 4180 / 100

= 41.8