organic chemistry - alkanes study guide

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organic

Study Guide

Organic Chemistry – Hydrocarbons - Alkanes

Q 1

• 1. Identify hydrocarbons.

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A 1

• 1. Contain only carbon and hydrogen• Important fuels• Base stock for the synthesis of many useful

compounds

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Q 2

• 1. List some common examples of hydrocarbons.

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A 2

• 2. Familiar examples: methane, propane, butane and octane

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Q 3

• 2. Identify alkanes.

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A 3

• 3. Contain only hydrogen and carbon• Only single covalent bonds

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Q 4

• What is the general formula for alkanes?

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A 4

• 4. Alkanes all fit this formula scheme:• CnH2n+2 where n can be any whole number

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Q 5

• 5. What are the names and uses of the first 10 alkanes?

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A 5

• Methane, CH4 fuel, major component of natural gas

• Ethane, C2H6 fuel, component of natural gas

• Propane, C3H8 fuel, LPG bottled gas

• Butane, C4H10 fuel, cigarette lighters

• Pentane, C5H12 fuel, component of gasoline

• Hexane, C6H14 fuel, component of gasoline

• Heptane, C7H16 fuel, component of gasoline

• Octane, C8H18 fuel, major component of gasoline

• Nonane, C9H20 fuel, component of gasoline

• Decane, C10H22 fuel, component of gasoline

• Memorize these.11

Q 6

• What the molecular and structural formulas for ethanol?

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A 6

• 6. Ethanol has the formula C2H5OH

• Structural formula:

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Ball and Stick Model

Lewis Model

Q 7

• At room temperature, 25 C, how many alkanes (C1 –C14) are gases?

• At 25 C, how many are liquids? Solids?

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A 7

• At room temperature, 25 C, how many alkanes (C1 –C14) are gases? ? 4, methane, ethane, propane and butane

• At 25 C, how many are liquids? 9, pentane through tetradecane, (C14H30) Solids? Zero

• Alkanes from C18H40 on up (C19, C20, C21 …) all have melting points above 25 C. Therefore they are solids at room temperature.

• Note: for the alkanes C11 – C19, the following prefixes are used.

• uni = 1, do (or di) = 2, tri = 3, tetra = 4, penta = 5, hexa = 6, hepta = 7, octa = 8, nona = 9. Example: C17H36 = heptadecane

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Q 8

• What are the names for:• C13H28?

• C18H40?

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A 8

• C13H28? tridecane

• C18H38? octadecane

• Rule: For alkanes 11-19, add the prefix, when that number is added to 10, equals the number of carbons in the “backbone” of the alkane in question. The “names run together”, as in heptadecane, C17H36.

• You should be able to write the correct names for the normal alkanes, C1 – C19.

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Q 9

• Identify three other families of hydrocarbons.

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A 9

• (1) Cycloalkanes CnH2n

• (2) Alkenes CnH2n Unsaturated hydrocarbons

• CnH2n

• (3) Aromatics (arenes) Ring compounds with alternating single

• (C-C) and double (C=C) carbon to carbon bonds. C/H of atoms in the aromatics is about 1:1 as in benzene, C6H6 (the only one you need to know!).

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Q 11

• Define structural isomers.

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A 11

• Compounds that have the same molecular formulas but different structural formulas.

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Q 12

• Referring to the structural isomers of C5H12,

• As branching increases what happens to the boiling points of these isomers?

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A 12

• As the branching increases, the boiling points decrease.

• That is because the longer molecules can interact with each other and “stick together” a little tighter than can their branched, more compact structural isomers. These branched forms have less surface area to stick to each other. Therefore the branched forms boil at a lower temperature than do their linear isomers.

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Q 13

• The most important alkane reaction is __________. Otherwise, alkanes are relatively _______ chemically.

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A 13

• The most important alkane reaction is combustion. Otherwise, alkanes are relatively stable chemically.

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Q 14

• What three common alkanes are found in the home?

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A 14

• Paraffin wax, mineral oil and petroleum jelly

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Q 15

• A. Which of the largest four petroleum companies had the greatest sales in dollars for 2007?

• B. Which had the greatest profit as a % of sales?

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A 15

• A. Royal Dutch Shell

• B. Exon

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Q 16

• What are five natural sources of alkanes?

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A 16

• Petroleum, natural gas, coal, methanogen bacteria, and cattle

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Q 17

• Where were petroleum and natural gas formed?

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A 17

• They were formed from microscopic phytoplankton and zooplankton in ancient marine and freshwater environments.

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Q 18

• Briefly describe the process of petroleum formation.

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A 18

• Petroleum and NG form under anoxic conditions (lack of oxygen) when dead plankton drift to the ocean bottom (benthos) and are covered by sediments. The organic molecules are deprived of oxygen (anoxic). Over time these organic compounds are gradually converted to alkanes. Pressures and temperatures are high.

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Q 19

• Explain how sugar can be converted to methane.

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A 19

• Sugar, under high pressure and temperature, anoxically decomposes to carbon dioxide and methane.

• Sugar carbon dioxide and methane

Energy + C6H12O6 CO2 + CH4

Balanced:

Energy + C6H12O6 3 CO2 + 3 CH4

This is an endothermic process (energy input required)

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Q 20

• What does the preponderance of evidence suggest concerning the consumption of petroleum?

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A 20

• The preponderance of evidence suggests that the world’s consumption of petroleum and natural gas is out pacing it’s natural rate of production. In other words we are rapidly running out of these resources.

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Q 21

• What is the Hubbert curve?

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A 21

• It is a model for predicting the exploitation of geological resources.

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Q 22

• Which areas of the world’s oceans have the lowest photosynthetic rates?

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A 22

• With a few exceptions, the lowest rate areas are located in the open tropical oceans of both the northern and southern hemispheres.

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Q 24

• Petroleum is formed in an _________of favorable temperature and pressure in the sedimentary rock below the oil deposit.

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A 24

• Petroleum is formed in an “oil window” of favorable temperature and pressure in the sedimentary rock below the oil deposit.

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Q 25

• Describe a normal petroleum deposit.

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A 25

• Petroleum is a complex mixture of alkanes, cycloalkanes, unsaturated hydrocarbons, as well as other carbon compounds. These deposits will often contain (1) an upper layer of gases,(2) a middle layer of liquid/solid materials (mostly organic compounds) with (3) a lower layer of saline water.

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Q 26

• Identify three approaches to oil refining?

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A 26

• (1) Fractional distillation: Relies on differences in boiling points to separate compounds from the petroleum mixture

• (2) Hydrocarbon Cracking: Using energy and catalysts, large molecules are broken down into smaller molecules.

• (3) Organic synthesis: Special products called petroleum derivatives are produced using specific chemical processes.

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Q 27

• Question 27 is missing.

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Q 28

• What is gasoline?

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A 28

• Gasoline is a mixture of alkanes, usually in the range of C4 to C10

• These molecules can be “straight” chains or “branched”

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Q 29

Identify: octane rating.

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A 29

• Octane Rating is a measure of the “auto-ignition” properties of a fuel in a spark - ignition internal combustion engine. In other words, the fuel’s “anti-knock” characteristics.

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Q 30

• Fuels are compared to 2,2,4-trimethyl pentane (iso-octane) ____octane and n-heptane ____ octane

• What is compared? The anti-knock characteristics of the fuel.

• If a fuel performs as does a mixture of 90% 2,2,4 trimethylpentane (iso-octane) and 10% n-heptane, then the fuel is rated as _____ and so on….

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A 30

• Fuels are compared to 2,2,4-trimethyl pentane (iso-octane) 100 octane and n-heptane zero octane

• What is compared? The anti-knock characteristics of the fuel.

• If a fuel performs as does a mixture of 90% 2,2,4 trimethylpentane (iso-octane) and 10% n-heptane, then the fuel is rated as 90 octane and so on….

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Q 32

• Identify: (R+M)/2)

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A 32

• (R+M)/2) = the average octane value and is reported in the U.S.A as the octane rating

• All the same: Road Octane Number (RdON), Pump Octane Number (PON),

or (R+M)/2.

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Q 31

• Balance the following using whole numbers.

• A. methane + oxygen carbon dioxide + water• B. hexane + oxygen carbon dioxide + water• C. Decane + oxygen carbon dioxide + water• D. Tetradecane + oxygen carbon dioxide +

water

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A 31

• A. CH4 + 2 O2 CO2 + 2 H2O

• B. 2 C6H14 + 19 O2 12 CO2 + 14 H2O

• C. 2 C10H22 + 31 O2 20 CO2 + 22 H2O

• D. 2 C14H30 + 43 O2 28 CO2 + 30 H2O

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Q 33

• Every gallon of gasoline consumed produces about _____________________.

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A 33

• Every gallon of gasoline consumed produces about 19 pounds of carbon dioxide gas.

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Q 34

• Identify several climate sensitive systems.

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A 34

• .(1) Human health,(2) agriculture, (3) natural ecosystems, (4) coastal areas, and (5) heating and cooling requirements are examples of climate-sensitive. systems

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Q 35

• Explain how the arctic tundra system is being changed by global warming.

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A 35

• The Arctic is expected to experience the greatest rates of warming compared with other world regions

• As permafrost melts, methane and CO2 are released from the frozen soil.

• Methane is a greenhouse gas (25 times more potent than CO2)

• The permafrost system seems to be in a positive feedback mode (higher temperatures increase the melting and release of more GHG’s higher temperatures and so on)

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Q 36

• _______ have relatively low toxicity.• Aromatic hydrocarbons _______have

relatively _____ toxicity.

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A 36

• Alkanes have relatively low toxicity.• Aromatic hydrocarbons (arenes) have

relatively high toxicity.

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Q 37

• ______________to high levels of benzene can cause leukemia. 

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A 37

• Long-term exposure to high levels of benzene can cause leukemia. 

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Q 38

• Describe the molecular structures of soaps and detergents. How are they similar? Different?

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A 38

• Both soaps and detergents have long-tails of “nonpolar alkane-like” hydrocarbons. These tails dissolve into the oil.

• Nonpolar alkane-like tail

• CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2OSO3-1 Na+1

• Polar head

• The “ polar heads”,CH2OSO3-1 Na+1, of detergents, are

different in that soaps contain carbon instead of sulfur. Both act similarly in that the polar heads dissolve into the water. This action reduces the oil to micro- droplets which easily disperse.

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Q 39

• Certain types of _________ can metabolize alkanes.

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A 39

• Certain types of bacteria can metabolize alkanes.

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Q 40

• ________ are derivatives of hydrocarbons as we saw with the synthesis of ethanol from ethene and water.

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A 40

• Alcohols are derivatives of hydrocarbons as we saw with the synthesis of ethanol from ethene and water.

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Q 41

• How is ethene different from ethane?

• This difference allows ethene to be readily converted to ______ using water and a catalyst.

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A 41

• How is ethene different from ethane?• Ethene contains a very chemically active

double bond. This bond can be broken readily and functional groups can be added to the molecule.

• This difference allows ethene to be readily converted to ethanol using water and a catalyst.

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Q 42

• The common name for ethane-1,2-diol is__________, or antifreeze, a toxic liquid.

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A 42

• The common name for ethane-1,2-diol is ethylene glycol, or antifreeze, a toxic liquid.

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Q 43

• What are some uses of ethane-1,2-diol?

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A 43

• What are some uses of ethane-1,2-diol?

• Ethane-1,2-diol is used as antifreeze and as a precursor for plastics.

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Q 44

• What are the two major categories of plastics and which can be recycled?

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A 44

• What are the two major categories of plastics and which can be recycled?

• Plastics is divided into 2 major categories - thermoplastics and thermosets.

• Thermoplastics can be recycled; thermosets can not.

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Q 45

• Provide two examples of each plastics category?

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A 45

• Provide two examples of each plastics category?

• Thermoplastics: Polyethylene (PE)Polyvinyl Chloride (PVC)

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Thermosets: Vulcanized Rubber• Urea Formaldehyde (UF)

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