Section 3: Organic Chemistry

Question 1

Define a hydrocarbon?

Answer 1

a molecule that is made up only of hydrogen and carbon atoms

Question 2

What is the general formula for all alkanes?

Answer 2

CnH2n+2

Question 3

what is the name of the alkane with a molecular formula of CH4?

Answer 3

Methane

Question 4

what is the molecular formula of ethane?

Answer 4

C2H6

Question 5

what is the name of the alkane with a molecular formula of C3H8?

Answer 5

Propane

Question 6

What is the molecular formula of butane?

Answer 6

C4H10

Question 7

What is the name of C5H12?

Answer 7

Pentane

Question 8

What is a homologous series?

Answer 8

a group of compounds that can all be represented by the same molecular formula

Question 9

How many covalent bonds can a carbon atom form?

Answer 9

4

Question 10

How many covalent bonds can a hydrogen atom form?

Answer 10

1

Question 11

If an alkane is saturated, what does this mean?

Answer 11

the carbon atoms have formed four bonds and the hydrogen atoms have formed 1, no carbon carbon double bonds

Question 12

write the word equation for complete combustion

Answer 12

alkane + oxygen –> carbon dioxide + water (+energy)

Question 13

what colour is the flame when gas burns in complete combustion?

Answer 13

clean blue

Question 14

write the word equation for incomplete combustion

Answer 14

alkane + oxygen –> carbon + carbon monoxide + carbon dioxide + water (+energy)

Question 15

In the presence of ultraviolet light, alkanes react with halogens to form what?

Answer 15

haloalkenes

Question 16

the reaction between an alkane and a halogen is called a

Answer 16

substitution reaction

Question 17

in incomplete combustion, the gas burns with what colour flame?

Answer 17

smoky yellow

Question 18

why is the reaction between an alkane and a halogen called a substitution reaction?

Answer 18

a hydrogen atom from the alkane is substituted by the halogen

Question 19

the prescence of what kind of light is required for a halogen to react with an alkane to form a haloalkane?

Answer 19

ultraviolet

Question 20

what distinguishes an alkene from an alkane, apart from its general formula?

Answer 20

alkenes have a double bond between two of the carbon atoms in their chain

Question 21

why are alkenes unsaturated?

Answer 21

because they can make more bonds if the double bond opens up

Question 22

what is the general formula for an alkene?

Answer 22

CnH2n

Question 23

what is the molecular formula of ethene?

Answer 23

C2H4

Question 24

what is the name of the alkene with a molecular formula of C3H6?

Answer 24

propene

Question 25

what is the molecular formula of butene?

Answer 25

C4H8

Question 26

what is an isomer?

Answer 26

molecules with the same molecular formulas but different structures (displayed formulas)

Question 27

halogens react with alkenes to form…

Answer 27

haloalkanes

Question 28

bromine and ethene react to form dibromethane. What kind of reaction is this and what happens when the two react?

Answer 28

an addition reaction,(as with all halogen/alkene reactions). The C=C double bond is split and a halogen atom is added to each of the carbons

Question 29

bromine molecules are orange, and dibromoalkane is colourless. Thus, when bromine and alkenes react what is the colour change? and what is this experiement used to test for?

Answer 29

colour change of orange –> colourless… tests for carbon-carbon double bonds

Question 30

ethene is produced from which raw material, by which process?

Answer 30

crude oil by cracking (see Section 5)

Question 31

ethene reacts with steam to make…

Answer 31

ethanol

Question 32

what conditions does the reaction of ethene + steam require?

1. pressure
2. temperature
3. catalyst

Answer 32

1. 60-70 atmospheres
2. 300 degrees C
3. phosphoric acid

Question 33

what is the alternative method of producing ethanol?

Answer 33

fermentation

Question 34

what is the raw material required for fermentation?

Answer 34

sugar, e.g glucose

Question 35

how is sugar converted to ethanol?

Answer 35

using yeast

Question 36

hat conditions are required for fermentation to occur?

1. temperature

Answer 36

30 degrees C (about)

Question 37

wht is the rate of reaction for the method of producing ethanol using ethene and steam compared to fermentation?

Answer 37

it is very fast, where fermentation is very slow

Question 38

what is the quality of product like when using fermentation to produce ethanol?

Answer 38

it is very impure, and needs further processing. It is also not very concentrated, and thus needs to be distilled to increase its strength

Question 39

two advantages of using the ethene + steam method of ethanol production?

Answer 39

product is pure, rate of reaction is very fast, labour costs are low

Question 40

two advantages of using fermentation as a method of ethanol production?

Answer 40

sugar & yeast are renewable resources, (whereas crude oil is a finite resource), cheap equipment needed due to low temp.

Question 41

cost of ethene + steam method?

Answer 41

low labour cost but expensive equipment needed due to high temp and pressure

Question 42

when ethanol is dehydrated, what is the product formed?

Answer 42

ethene

Question 43

what catalyst is needed in order to dehydrate ethnol and why?

Answer 43

hot aluminium oxide: it provides a large surface area for the reaction

Question 44

what is the symbol equation for the dehydration of ethanol to make ethene?

Answer 44

C2H5OH —> C2H4 + H2O