Chapter 21: Problem 120

A compound containing only carbon and hydrogen is \(85.63 \%\) C by mass. Reaction of this compound with \(\mathrm{H}_{2} \mathrm{O}\) produces a secondary alcohol as the major product and a primary alcohol as the minor product. (See Exercise 62.) If the molar mass of the hydrocarbon is between 50 and 60 g/mol, name the compound.

Short Answer

Expert verified

The compound is 2-butene, with the molecular formula C4H8. This hydrocarbon contains 85.63% carbon and 14.37% hydrogen, has a molar mass between 50 and 60 g/mol, and reacts with water to produce a secondary alcohol as the major product and a primary alcohol as the minor product.

Step by step solution

Calculate the mass percentage of hydrogen

Since the compound contains only carbon and hydrogen, the mass percentage of hydrogen can be found by subtracting the mass percentage of carbon from 100%. Mass percentage of Hydrogen (H) = 100 - 85.63 = 14.37%

Determine a reasonable ratio of C atoms to H atoms

Using the mass percentages we found in step 1 and the molar masses of carbon and hydrogen, we can find a reasonable ratio of C atoms to H atoms that would lie close to an integer. Molar mass of carbon (C) = 12 g/mol Molar mass of hydrogen (H) = 1 g/mol Moles of carbon = mass percentage of carbon (C) / atomic mass of carbon (C) = 85.63 / 12 Moles of hydrogen = mass percentage of hydrogen (H) / atomic mass of hydrogen (H) = 14.37 / 1 C:H mole ratio (rounded to nearest whole numbers) = (85.63 / 12):(14.37 / 1) = 7:14 which can be simplified to 1:2.

Propose the molecular formula

Based on the mole ratio we found in step 2, the molecular formula can be assumed to be CnH2n. As we know that the molar mass is between 50 and 60 g/mol, substituting the various values of 'n' into the formula will help us find which number of carbon atoms match the given molar mass range. When n = 4, Molar mass of CnH2n = 4 × 12 + 2 × 4 × 1 = 48 + 8 = 56 g/mol. This falls into the given range.

Consider potential carbon structures

Since we found that there are 4 carbon atoms and 8 hydrogen atoms in the hydrocarbon (C4H8), we have to think about potential carbon structures that would give a major product as a secondary alcohol and a minor product as a primary alcohol when reacted with water. The most reasonable structure that would produce this result is 2-butene. We can represent the compound as: \(CH_{3}-CH=CH-CH_{3}\) So, the name of the compound is 2-butene.

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Short Answer

Step by step solution

Calculate the mass percentage of hydrogen

Determine a reasonable ratio of C atoms to H atoms

Propose the molecular formula

Consider potential carbon structures

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