1.13: Organic Chemistry- Alkanes and Halogenated Hydrocarbons (Exercises)

12.1: Organic Chemistry

Concept Review Exercises

1. Classify each compound as organic or inorganic.

   1. C₃H₈O
   2. CaCl₂
   3. Cr(NH₃)₃Cl₃
   4. C₃₀H₄₈O₃N

2. Which compound is likely organic and which is likely inorganic?

   1. a flammable compound that boils at 80°C and is insoluble in water
   2. a compound that does not burn, melts at 630°C, and is soluble in water

3. Classify each compound as organic or inorganic.

   1. C₆H₁₀
   2. CoCl₂
   3. C₁₂H₂₂O₁₁

4. Classify each compound as organic or inorganic.

   1. CH₃NH₂
   2. NaNH₂
   3. Cu(NH₃)₆Cl₂

5. Which member of each pair has a higher melting point?

   1. CH₃OH and NaOH
   2. CH₃Cl and KCl

6. Which member of each pair has a higher melting point?

   1. C₂H₆ and CoCl₂
   2. CH₄ and LiH

Answers

1. 1. organic
   2. inorganic
   3. inorganic
   4. organic

2.  

   1. organic
   2. inorganic

    

3. a. organic   b. inorganic  c.  organic


4.  

5.

1. NaOH
2. KCl

12.3: Branched-Chain Alkanes

Concept Review Exercises

1. In alkanes, can there be a two-carbon branch off the second carbon atom of a four-carbon chain? Explain.

2. A student is asked to write structural formulas for two different hydrocarbons having the molecular formula C₅H₁₂. She writes one formula with all five carbon atoms in a horizontal line and the other with four carbon atoms in a line, with a CH₃ group extending down from the first attached to the third carbon atom. Do these structural formulas represent different molecular formulas? Explain why or why not.

Answers

1. No; the branch would make the longest continuous chain of five carbon atoms.

2. No; both are five-carbon continuous chains.

Key Takeaway

• Alkanes with four or more carbon atoms can exist in isomeric forms.

Exercises

1. Briefly identify the important distinctions between a straight-chain alkane and a branched-chain alkane.

2. How are butane and isobutane related? How do they differ?

3. Name each compound.

   1. 
   2. 

4. Write the structural formula for each compound.

   1. hexane
   2. octane

5. Indicate whether the structures in each set represent the same compound or isomers.

   1. CH₃CH₂CH₂CH₃ and

      

   2. CH₃CH₂CH₂CH₂CH₃ and

      

Answers

1. Straight-chain alkanes and branched-chain alkanes have different properties as well as different structures.

 

3.  

   1. pentane
   2. heptane

 

5.  

   1. not isomers, same compound
   2. yes, isomers

12.4: Condensed Structural and Line-Angle Formulas

Exercises

1. Write the condensed structural formula for each structural formula.

   1. 
   2. 
   3. 

2. A condensed structural formula for isohexane can be written as . Draw the line-angle formula for isohexane.

3. Draw a line-angle formula for the compound 

4. Give the condensed structural formula for the compound represented by this line-angle formula:

   

Answers

1.  

   1. CH₃CH₃
   2. CH₃CH₂CH₃
   3. CH₃CH₂CH₂CH₂CH₃

 

3. 

    

    

 

12.5: IUPAC Nomenclature

Concept Review Exercises

1. What is a CH₃ group called when it is attached to a chain of carbon atoms—a substituent or a functional group?
2. Which type of name uses numbers to locate substituents—common names or IUPAC names?

Answers

1. substituent

2. IUPAC names

 

Exercises

1. Briefly identify the important distinctions between an alkane and an alkyl group.

2. How many carbon atoms are present in each molecule?

   1. 2-methylbutane
   2. 3-ethylpentane

3. How many carbon atoms are present in each molecule?

   1. 2,3-dimethylbutane
   2. 3-ethyl-2-methylheptane

4. Draw the condensed structure for each compound.

   1. 3-methylpentane
   2. 2,2,5-trimethylhexane
   3. 4-ethyl-3-methyloctane

5. Draw the condensed structure for each compound.

   1. 2-methylpentane
   2. 4-ethyl-2-methylhexane
   3. 2,2,3,3-tetramethylbutane

6. Name each compound according to the IUPAC system.

   1. 
   2. 

7. Name each compound according to the IUPAC system.

   1. 
   2. 

8. What is a substituent? How is the location of a substituent indicated in the IUPAC system?

9. Briefly identify the important distinctions between a common name and an IUPAC name.

Answers

1. An alkane is a molecule; an alkyl group is not an independent molecule but rather a part of a molecule that we consider as a unit.

 

3.  

   1. 6
   2. 10

 

5.  

   1. 
   2. 
   3. 

 

7.  

   1. 2,2,4,4-tetramethylpentane
   2. 3-ethylhexane

 

9. Common names are widely used but not very systematic; IUPAC names identify a parent compound and name other groups as substituents.

12.6: Physical Properties of Alkanes

12.7: Chemical Properties of Alkanes

12.8: Halogenated Hydrocarbons

12.9: Cycloalkanes

12.10: Chapter Summary

Additional Exercises

1. You find an unlabeled jar containing a solid that melts at 48°C. It ignites readily and burns readily. The substance is insoluble in water and floats on the surface. Is the substance likely to be organic or inorganic?

2. Give the molecular formulas for methylcyclopentane, 2-methylpentane, and cyclohexane. Which are isomers?

3. What is wrong with each name? (Hint: first write the structure as if it were correct.) Give the correct name for each compound.

   1. 2-dimethylpropane
   2. 2,3,3-trimethylbutane
   3. 2,4-diethylpentane
   4. 3,4-dimethyl-5-propylhexane

4. What is the danger in swallowing a liquid alkane?

5. Distinguish between lighter and heavier liquid alkanes in terms of their effects on the skin.

6. Following is the line formula for an alkane. Draw its condensed structure and give its name.

   

7. Write equations for the complete combustion of each compound.

   1. propane (a bottled gas fuel)
   2. octane (a typical hydrocarbon in gasoline).

8. Skip

9. Draw the structures for the five isomeric hexanes (C₆H₁₄). Name each by the IUPAC system.

10. Indicate whether the structures in each set represent the same compound or isomers.

    1. 
    2. 
    3. 

11. Consider the line-angle formulas shown here and answer the questions.

    

    1. Which pair of formulas represents isomers? Draw each structure as condensed.
    2. Which formula represents an alkyl halide? Name the compound and write its condensed structural formula.
    3. Which formula represents a cyclic alkane? Name the compound and draw its structure.
    4. What is the molecular formula of the compound represented by (i)?

Answers

1. organic

 

3.  

   1. Two numbers are needed to indicate two substituents; 2,2-dimethylpropane.
   2. The lowest possible numbers were not used; 2,2,3-trimethylbutane.
   3. An ethyl substituent is not possible on the second carbon atom; 3,5-dimethylheptane.
   4. A propyl substituent is not possible on the fifth carbon atom; 3,4,5-trimethyloctane.

 

5. Lighter alkanes wash away protective skin oils; heavier alkanes form a protective layer.

 

7.  

   1. C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
   2. 2C₈H₁₈ + 25O₂ → 16CO₂ + 18H₂O

 

9. CH₃CH₂CH₂CH₂CH₂CH₃; hexane

   

   

   

   

 

11.  

    1. ii and iii; CH₃CH₂CH₂CH₂CH₂CH₂CH₃ and

       
    2. iv; 3-chloropentane; 

    3. i; ethylcyclopentane;

       
    4. C₇H₁₄