Brainlag PlusMr and the percentage of carbon in a hydrocarbon or alcohol, moles and masses of carbon dioxide from burning a fuel, gas volumes, and estimating boiling points from a homologous series.
Mr and percentage of carbon
Add up the relative atomic masses of every atom in the formula.
Then:
percentage of carbon = (12 × number of C atoms) ÷ Mr × 100
You must recall this: there is no chemistry equation sheet.
- Hexane, C₆H₁₄ (C = 12, H = 1)
- Mr = 6 × 12 + 14 × 1 = 86
- mass of carbon = 6 × 12 = 72
- % carbon = 72 ÷ 86 × 100 = 83.7 % (1 d.p.)
Multiply 12 by the number of carbon atoms. 12 ÷ 86 × 100 gives 14.0 %, which is far too low for a hydrocarbon.
The rest of this lesson and its 10 practice questions are in Plus.
Screen 1 of 4, free to read.
- 10 exam-style questions, marked as you go, each with a worked solution
- The Molar Mass Calculator beside every question
- Anything you get wrong is saved to your flashcards