Lesson: Chapter 7 — Quantification of Elements and Compounds

7.2. Relative molecular mass 8 of 10 Reset answers

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Question 8

What is the formula mass of calcium carbonate (CaCO₃)? (A_r: C = 12, O = 16, Ca = 40)

A 68 B 100 C 52 D 116

The right answer is the one marked above.

100. CaCO₃ = 40 + 12 + (3 × 16) = 40 + 12 + 48 = 100.

68 comes from taking 40 + 12 + 16 and ignoring the subscript 3 on the oxygen. The 48 from three oxygens is nearly half the total.

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