Chemistry · Grades 10–12
Alcohol-family molar mass
For a saturated acyclic monohydric alcohol, CnH2n+2O, sum all atom masses. The formula is also compatible with ether isomers.
Rule and assumptions
For a saturated acyclic monohydric alcohol, CnH2n+2O, sum all atom masses. The formula is also compatible with ether isomers.
CₙH₂ₙ₊₂O; M = 12n + (2n + 2) + 16
Worked examples
Use C = 12, H = 1 and O = 16 g/mol. An acyclic saturated monohydric alcohol has formula CₙH₂ₙ₊₂O with n = 5. Find its molar mass. Round to 3 decimal places if needed. Answer in g/mol.
CₙH₂ₙ₊₂O; M = 12n + (2n + 2) + 16 12 × 5 + (2 × 5 + 2) + 16 = 88
88 g/mol
Use C = 12, H = 1 and O = 16 g/mol. An acyclic saturated monohydric alcohol has formula CₙH₂ₙ₊₂O with n = 7. Find its molar mass. Round to 3 decimal places if needed. Answer in g/mol.
CₙH₂ₙ₊₂O; M = 12n + (2n + 2) + 16 12 × 7 + (2 × 7 + 2) + 16 = 116
116 g/mol
Try two questions
Use C = 12, H = 1 and O = 16 g/mol. An acyclic saturated monohydric alcohol has formula CₙH₂ₙ₊₂O with n = 17. Find its molar mass. Round to 3 decimal places if needed. Answer in g/mol.
Use C = 12, H = 1 and O = 16 g/mol. An acyclic saturated monohydric alcohol has formula CₙH₂ₙ₊₂O with n = 14. Find its molar mass. Round to 3 decimal places if needed. Answer in g/mol.
Answers and reasoning
Answers and marking notes
- 256 g/mol
CₙH₂ₙ₊₂O; M = 12n + (2n + 2) + 16 12 × 17 + (2 × 17 + 2) + 16 = 256
- 214 g/mol
CₙH₂ₙ₊₂O; M = 12n + (2n + 2) + 16 12 × 14 + (2 × 14 + 2) + 16 = 214
Further reading and review references
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