HW: 10.44

Which formula represents an unsaturated hydrocarbon?

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How many electrons are shared between the carbon atoms in a molecule of ethyne?

• 6

• 2

• 3

• 4

Answer explanation

In ethyne (C2H2), the two carbon atoms are connected by a triple bond, which consists of three shared pairs of electrons. Therefore, a total of 6 electrons are shared between the carbon atoms.

What is the general formula for the homologous series that includes ethyne?

• C_nH_n

• C_nH_2n

• C_nH_2n+2

• C_nH_2n-2

Answer explanation

Ethyne (C2H2) belongs to the alkyne homologous series, which follows the general formula CnH2n-2. This formula accounts for the triple bond in alkynes, distinguishing them from alkanes and alkenes.

Which name represents a hydrocarbon?

• 1-hexene

• 1-iodohexane

• 3-hexanone

• 3-hexanol

Answer explanation

1-hexene is a hydrocarbon as it contains only carbon and hydrogen atoms, with a double bond. The other options contain functional groups (iodo, ketone, alcohol) that classify them as non-hydrocarbons.

Which formula represents a hydrocarbon?

• CO₂

• C₃H₈

• C₂H₄O₂

• C₃H₈O

Answer explanation

A hydrocarbon consists only of carbon (C) and hydrogen (H) atoms. The formula C3H8 contains only carbon and hydrogen, making it a hydrocarbon. The other options include oxygen, disqualifying them as hydrocarbons.

Given the formula representing a compound: What is a chemical name of this compound?

• 2,3,3-trimethylbutane

• 2-methyl-2-ethylbutane

• 2,3-dimethylpentane

• 2,3-ethylpentane

Answer explanation

The compound's structure indicates three methyl groups on the second and third carbon of a butane chain, leading to the name 2,3,3-trimethylbutane. This matches the correct answer, distinguishing it from the other options.

Which formula represents 2-butene?

• [See diagram 1]

• [See diagram 2]

• [See diagram 3]

• [See diagram 4]

Answer explanation

2-butene is an alkene with the formula C4H8, characterized by a double bond between two carbon atoms. Diagram 2 correctly depicts this structure, showing the appropriate arrangement of carbon and hydrogen atoms.

Which statement describes the bonding in an alkyne molecule?

• There is at least one carbon-to-carbon double bond.

• There is at least one carbon-to-carbon triple bond.

• There is at least one carbon-to-oxygen single bond.

• There is at least one carbon-to-oxygen double bond.

Answer explanation

Alkynes are characterized by having at least one carbon-to-carbon triple bond, which distinguishes them from alkenes (with double bonds) and alkanes (with single bonds). Thus, the correct statement is that there is at least one carbon-to-carbon triple bond.

What is the IUPAC name of the compound?

• 2,3-dimethyloctane

• 2,3-dimethylhexane

• 4,5-dimethyloctane

• 4,5-dimethylhexane

Answer explanation

The correct IUPAC name is 2,3-dimethylhexane because the longest carbon chain has 6 carbons (hexane), and the substituents (methyl groups) are located on the 2nd and 3rd carbons if you flip it around, making it the proper designation.

The only two elements in alkenes and alkynes are

• carbon and nitrogen

• carbon and hydrogen

• oxygen and nitrogen

• oxygen and hydrogen

Answer explanation

Alkenes and alkynes are hydrocarbons, meaning they consist only of carbon and hydrogen atoms. Therefore, the correct answer is 'carbon and hydrogen', as the other options include elements not found in these compounds.