Quiz

QUIZ

1. If there are n carbon atoms on an alkane, how many hydrogen atoms are there on the molecule?

a. 2n b. 2n + 2

c. 2n + 4 d. 3n

Answer: b. If there are n carbon atoms, there will be 2n + 2 hydrogen atoms on the alkane. This best indicates a completely saturated hydrocarbon molecule.

2. What can be said specifically about n-hexane as opposed to other types of hexane?

a. It doesn’t have a double bond while other types of hexanes do. b. It is branched, while other types of hexanes are not branched. c. It is not branched, while other types of hexanes are branched. d. It is much more combustible than other forms of hexane.

Answer: c. The n in front of the alkane, as in n-hexane, means it isn’t branched, while other forms of the alkane are possibly branched.

3. A carbon atom with four CH3 molecules attached to it is called what?

a. Isobutane b. Tert-pentane c. Sec-butane d. Neopentane

Answer: d. Neopentane is a carbon atom with four CH3 molecules attached to it. It is a cross-shaped molecule that has a total of 5 carbon atoms but an unusual shape.

4. If you have an ethyl group on the third carbon and a methyl group on the fourth carbon atom of a seven-carbon chain of an alkane, what is this called?

a. 3,4 ethyl methyl heptane b. 3-ethyl, 4-methyl heptane c. Iso methyl, 3-ethyl heptane d. 4-methyl, 5-ethyl heptane

Answer: b. The lowest numbers should be used and the molecule’s side chains should be in alphabetical order. This means that the molecule is a heptane and that 3 should be used to describe the ethyl group and 4 should be used to describe the methyl group.

5. Which cycloalkane has the greatest ring strain associated with it?

a. Cyclooctane b. Cycloheptane c. Cyclobutane d. Cyclopropane

Answer: d. Cyclopropane has the greatest ring strain associated with it because it has just a 60-degree angle between carbon atoms, which greatly differs from the ideal 109.5 degree-angle desired by the sp3 hybrid bond.

6. What is the smallest cycloalkane that has no ring strain associated with it?

a. Cyclopropane b. Cyclopentane c. Cyclohexane d. Cyclooctane

Answer: c. Cyclohexane has a bond angle that will be close to the desirable bond angle of 109.5 degrees; this will lead to no ring strain. In fact, there are no cycloalkanes greater than this size seen commonly in organic chemistry.

7. What is the smallest possible alkene molecule?

a. Pentene b. Butene c. Ethene d. Hexene

Answer: c. The smallest possible alkene molecule is C2H4 or ethene. It is impossible to have an alkene molecule with less than 2 carbon atoms to make the required double bond.

8. When the alkene molecule has side chains on opposite sides of the double bond, what can the designation be in order to describe this?

a. L-alkene b. E-alkene c. Z-alkene d. Cis-alkene

Answer: b. The term E-alkene refers to the German word “entgegen”, which means “opposite” using the E-Z designation. There is also a cistrans designation but, in alkenes, there is not an L-D designation.

9. What happens to the melting point of alkenes as they get bigger or longer?

a. The melting point will be greater if it is a cis molecule versus a trans molecule. b. The melting point is much higher than corresponding alkanes. c. The melting point will be lower with increased molecular weight. d. The melting point will increase with increased molecular weight.

Answer: c. The melting point will increase with increased molecular weight and will be lower in a cis versus a trans molecule.

10. Alkynes with n carbon atoms will have how many hydrogen atoms associated with it?

a. 2n b. 2n – 2

c. 2n + 2 d. 2n – 4

Answer: b. If the number of carbon atoms is n, there will be 2n – 2 hydrogen atoms associated with it in any alkyne.