Hydrocarbons and Naming Alkanes: Quiz

Hydrocarbons and Naming Alkanes: Quiz

7 questions

1. Question 1EasyWhich is the general formula of the alkanes?

   ACₙH₂ₙBCₙH₂ₙ₊₂CCₙH₂ₙ₋₂DCₙHₙ
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   Answer: CₙH₂ₙ₊₂

   Alkanes have only single bonds, so each carbon carries the maximum number of hydrogens: CₙH₂ₙ₊₂ (e.g. C₃H₈). CₙH₂ₙ is the alkenes and CₙH₂ₙ₋₂ the alkynes.

2. Question 2EasyWhat is the molecular formula of heptane?

   AC₇H₁₄BC₇H₁₆CC₆H₁₄DC₇H₁₂
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   Answer: C₇H₁₆

   Hept- means 7 carbons; for an alkane, H = 2(7) + 2 = 16.

3. Question 3MediumWhat is the IUPAC name of CH₃CH₂CH₂CH(CH₃)CH₃?

   A4-methylpentaneB2-methylpentaneC1,1-dimethylbutaneDhexane
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   Answer: 2-methylpentane

   The longest chain has 5 carbons. Numbering from the end nearer the branch puts the methyl on carbon 2, not 4. (Hexane is an isomer, but it is the unbranched chain.)

4. Question 4MediumHow many structural isomers have the formula C₅H₁₂?

   A2B3C4D5
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   Answer: 3

   Pentane, 2-methylbutane and 2,2-dimethylpropane.

5. Question 5MediumWhich of these names is correct?

   A2-ethylbutaneB3-methylpentaneC1-methylbutaneD2-dimethylpropane
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   Answer: 3-methylpentane

   2-Ethylbutane and 1-methylbutane miss the longest chain (they are 3-methylpentane and pentane). "2-dimethyl" needs two locants: 2,2-dimethylpropane.

6. Question 6MediumWhich compound has the highest boiling point?

   AbutaneB2,2-dimethylpropaneC2-methylbutaneDpentane
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   Answer: pentane

   Pentane is the largest unbranched molecule here: it has the most surface contact and the strongest dispersion forces (36 °C). Branching lowers the boiling point, and butane is smaller.

7. Question 7HardIn 2C₄H₁₀ + 13O₂ → 8CO₂ + 10H₂O, how many moles of O₂ does 1 mol of butane need?

   A4 molB6.5 molC13 molD9 mol
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   Answer: 6.5 mol

   1 mol C₄H₁₀ × (13 mol O₂ / 2 mol C₄H₁₀) = 6.5 mol O₂.