O Levels Chemistry (5070)•5070/12/M/J/22
Explanation
Relative formula mass of Na₂CO₃
Steps:
- Formula of anhydrous sodium carbonate is Na₂CO₃.
- Atomic masses: Na = 23, C = 12, O = 16.
- Compute: (2 × 23) + 12 + (3 × 16) = 46 + 12 + 48.
- Sum equals 106.
Why C is correct:
- Relative formula mass is the sum of atomic masses in the formula Na₂CO₃, yielding 106.
Why the others are wrong:
- A: Matches NaOH (23 + 16 + 12? No, incorrect for carbonate).
- B: Matches Na₂CO₃ minus one O (92 - 9? Partial calculation error).
- D: Matches hydrated form like Na₂CO₃·H₂O (106 + 18 = 124).
Final answer: C
Topic: Relative masses of atoms and molecules
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