DF3 - Hydrocarbons

Question 1

What is fractional distillation?

Answer 1

When crude oil is heated to vaporise it + the vapour passes into a distillation column

Question 2

What is a homologous series?

Answer 2

A group of compounds that have a similar structure/ the same general formula

Question 3

Give an example of a homologous series

Answer 3

Alkanes

Question 4

What is catenation?

Answer 4

The bonding of atoms of the same element into a chain/ring. Carbon can form strong covalent bonds with itself to give chains/rings

Question 5

How many bonds can carbon form?

Answer 5

4 covalent bonds

Question 6

What are hydrocarbons?

Answer 6

Compounds containing only carbon and hydrogen

Question 7

Name 4 types of hydrocarbon

Answer 7

Alkanes, alkenes, arenes + cycloalkanes

Question 8

What is the general formula for alkanes?

Answer 8

C n H 2n+2

Question 9

What is the general formula for alkenes?

Answer 9

C n H 2n

Question 10

What is the general formula for arenes?

Answer 10

C n H n

Question 11

What is the general formula for cycloalkanes?

Answer 11

C n H 2n

Question 12

What are aromatic compounds?

Answer 12

Compounds that contain one or more benzene rings

Question 13

What are aliphatic compounds?

Answer 13

Compounds that do not contain any benzene rings

Question 14

Which 2 types of hydrocarbons are more unreactive out of the 4?

Answer 14

Alkanes + arenes

Question 15

What are functional groups?

Answer 15

Modifiers that are responsible for the characteristic chemical reactions of molecules (but when added to a hydrocarbon framework it can change its properties)

Question 16

Which one is more reactive, a c-c or c=c bond?

Answer 16

A c=c double bond (in alkenes)

Question 17

Are alkanes saturated or unsaturated?

Answer 17

Saturated

Question 18

What does it mean if alkanes are saturated?

Answer 18

They contain the maximum number of hydrogen atoms possible (no double/triple bonds)

Question 19

Name the first 10 alkanes

Answer 19

Methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane + decane

Question 20

Are the chemical properties the same for all of the compounds in a homologous series?

Answer 20

They all have similar chemical properties

Question 21

Are the physical properties the same for all of the compounds in a homologous series?

Answer 21

Physical properties e.g boiling/melting point + density change gradually as no. of C atoms increase

Question 22

Describe molecular formula

Answer 22

Shows the no. of each type of atom present. Does not tell us anything about bonding within compound

Question 23

Describe empirical formula

Answer 23

Simplest ratio of the elements present in a molecule. Does not tell us anything about bonding within compound

Question 24

Describe condensed formula

Answer 24

Each carbon in the molecule is written out in turn, with the atoms attached to it written directly after. Brackets are used to indicate branching in the molecule, or multiple identical groups

Question 25

Describe displayed formula

Answer 25

Represents the molecule by showing all of the atoms, and all of the bonds between those atoms. Bonds are represented by lines, with the number of lines representing the strength of the bond (e.g 1 line is single bond and 2 lines is double bond)

Question 26

Describe structural/shortened structural formula

Answer 26

It is similar to display formula but not all bonds are shown. All atoms are still indicated using subscript numbers. Carbon hydrogen bonds are often simplified.

Question 27

Describe skeletal formula

Answer 27

The main carbon chain is represented as a zig-zagging line, where the end of lines and the vertices represent carbon atoms. Functional groups + atoms other than carbon/hydrogen are always shown

Question 28

What are two types of alkane chains?

Answer 28

straight chains and branched chains

Question 29

What are structural isomers?

Answer 29

When two compounds have the same molecular formula but different structural formulas

Question 30

Give a structural isomer of butane

Answer 30

Methylpropane

Question 31

Name at least 3 of the 5 common alkyl groups

Answer 31

``` Methyl: CH3 - Ethyl: CH3CH2 - Propyl: CH3CH2CH2 - Butyl: CH3CH2CH2CH2 - Pentyl: CH3CH2CH2CH2CH2 - ```

Question 32

What letter often represents side groups?

Answer 32

R

Question 33

How can you determine the systematic name of a hydrocarbon?

Answer 33

By using the full structural formula | Systematic name is derived from a set of rules

Question 34

What are the rules/steps to giving a systematic name to alkanes?

Answer 34

1. Name the longest chain 2. Identify any side chains off the main chain and name them 3. State the location of any side chains by prefixing the name of the side chain with the number of the carbon atom to which the side chain is attached 5. Keep the number as low as possible 6. If there is more than one side chain, rules still apply. When naming, state the side chain in alphabetical order. Use prefixes 'di' or 'tri' depending on how many of the same side chain you have 7. Name the compound by starting with the side chains + their location first, then the 'parent' chain. Use hyphens between numbers + letters + commas between numbers

Question 35

How do you name cycloalkanes?

Answer 35

1. Count the number of carbons in the cyclic structure + identify appropriate prefix to name the alkane 2. Add alkane name to the enf of 'cyclo' 3. If there are side chains same rules from alkanes apply

Question 36

The state of an alkane at room temp. is dependent on the number of carbon atoms (size of molecule). How many carbons are in solid, liquid and gas alkanes.

Answer 36

Colourless gases: n = 1-4 Colourless liquids: n = 5-16 White waxy solids: n = 17+

Question 37

Alkanes mix well with each other. Why don't they mix well with water?

Answer 37

- Alkanes + water form two separate layers - Alkanes contain non-polar molecules but liquids such as water contain polar molecules that attract each other + prevent alkane molecules from mixing with them

Question 38

Describe the structure of arenes

Answer 38

They have c-c and c=c bonds one after the other in a ring shape (in skeletal formula they are same as cycloalkanes apart from the fact they have a circle in the middle - delocalised electrons in there)