Halogenoalkanes

Question 1

what is a halogenoalkane ?

Answer 1

it is where a halogen takes place of a H atom in an alkane

Question 2

uses of halogenoalkanes ? (6)

Answer 2

-refrigerants
- bases of PVC
- solvents
- teflon
- pharmaceuticals
- anaesthetics

Question 3

in what way are halogenoalkanes the same as alkanes ?

Answer 3

they have the same carbon skeleton as an alkane

Question 4

how reactive are halogenoalkanes compared to alkanes ?

Answer 4

halogenoalkanes are much more reactive than alkanes

Question 5

general formula of halogenoalkanes ?

Answer 5

CnH2n+1 X
X = any halogen

Question 6

functional group of halogenoalkanes ?

Answer 6

R-X
R = a carbon chain that can vary

Question 7

prefixes of halogenoalkanes ?

Answer 7

iodo - , bromo - , fluoro- ,chloro-

Question 8

what are the 4 categories of physical properties of halogenoalkanes ?

Answer 8

• bond polarity
• solubility
• boiling point
• reactivity

Question 9

what is bond polarity associated with ?

Answer 9

electronegativity

Question 10

what is meant by electronegativity ?

Answer 10

the power of an atom to attract a pair of electrons in a covalent bond

Question 11

electronegativity of halogens from most to least ?

Answer 11

• fluorine
• chlorine
• bromine
• iodine

Question 12

why do some molecules become polar ?

Answer 12

due to the difference in electronegativity

Question 13

describe the electronegativity between C-F ?

Answer 13

fluorine is nearly twice as more electronegative than carbon
so electron density is more attracted to the fluorine, leaving carbon electron defficient ( delta positive) and Fluorine electron rich ( delta negative )

Question 14

how many carbon bonds with halogens are polar ?

Answer 14

all bonds are polar

Question 15

what happens to the bond polarity going up the group ?

Answer 15

bonds get more polar going up the group

Question 16

what kind of solvent is water ?

Answer 16

water is a polar solvent

Question 17

how is the solubility in water determined ?

Answer 17

solubility in water i determined by how strong the interactions are between the solvent ( water) and the solute that you try to dissolve

Question 18

are halogenoalkanes soluble in water ?

Answer 18

no the are insoluble in water

Question 19

why are halogenoalkanes insoluble in water ?

Answer 19

because even though the halogen to carbon bond is also polar, the attraction is not strong enough to make the halogenoalkane soluble in water
- also because they have large regions (r-groups) which are non-polar
so the carbon chain can only form van der waals forces

Question 20

where are halogenoalkanes most soluble ? and why ?

Answer 20

they are most soluble in hydrocarbons
- because they are non-polar

Question 21

what does the boiling point depend on ?

Answer 21

boiling point depends on the carbon chain length so the longer the chain the larger the boiling point

Question 22

why does the boiling point depend on the carbon chain length ?

Answer 22

because van der waals forces increase with chain length because there are more electrons in the molecule

Question 23

what factor reduces boiling point ? and why ?

Answer 23

branching of the chain
- because van der waals forces are weaker due to less surface area of contact for intermolecular forces to act

Question 24

what is the boiling point trend in group 7 ?

Answer 24

boiling point increases down the group

Question 25

why does the boiling point increase down the group ?

Answer 25

because the halogen is larger so has more electrons and greater van der waals forces which outweighs the polarity

Question 26

halogenoalkanes that are more polar and have more electrons have what kind of boiling point ?

Answer 26

have a higher boiling point

Question 27

what occurs almost every time when halogenoalkanes react ?

Answer 27

almost every time the C-X bond breaks

Question 28

what does the reactivity of the halogenoalkanes depend on ?

Answer 28

reactivity depends on the ease of C-X bond breaking so if the bond breaks more easily, it will be a more reactive halogenoalkane

Question 29

what factors does the ease of bond breaking depend on ?

Answer 29

- bond polarity - bond enthalpy

Question 30

what is meant by the term bond enthalpy ?

Answer 30

how much energy is required to break a covalent bond

Question 31

what is the trend of bond enthalpy in group 7 ?

Answer 31

bond enthalpy decreases going down the group

Question 32

how do you prove which one of the factors does ease depend on ?

Answer 32

by adding aqueous acidified silver nitrate solution to a halogenoalkane

Question 33

what occurs when you add aqueous acidified silver nitrate solution to halogenoalkanes ?

Answer 33

a hydrolysis reaction occurs C-X bond breaks halogen on ( X-) is released into the solution so you make a precipitate of the silver hallide ( Ag X )

Question 34

iodobutane bromobutane chlorobutane which precipitate forms first and what colour ?

Answer 34

iodine yellow

Question 35

iodobutane bromobutane chlorobutane which precipitate forms second and what colour ?

Answer 35

bromine cream

Question 36

iodobutane bromobutane chlorobutane which precipitate forms third and what colour ?

Answer 36

chlorine white

Question 37

what is the conclusion of the reactivity experiment ?

Answer 37

conclusion is that reactivity increases down the group so most significant property is the bond enthalpy

Question 38

what is meant by a nucleophile ?

Answer 38

a nucleophile has a lone pair of electrons on an electronegative atom - so they are negatively charged or delta negative

Question 39

how do nucleophiles act ?

Answer 39

nucleophiles act by using their lone pair of electrons to form a new bond

Question 40

what do nucleophiles form a bond between ?

Answer 40

form a new bond with something that is delta negative

Question 41

what are the 3 possible nucleophiles in nucleophilic substitution ?

Answer 41

- OH- hydroxide ion - CN- cyanide ion - NH3 ammonia

Question 42

what does a nucleopjilic substitution with a hydroxide ion create ?

Answer 42

an alcohol and a halogen ion

Question 43

what does a nucleopjilic substitution with a cyanide ion create ?

Answer 43

a nitrate / nitrile and a halogen ion

Question 44

what does a nucleopjilic substitution with ammonia create ?

Answer 44

an amine and ammonium-halogen

Question 45

what does the rate of substitution depend on ?

Answer 45

the halogen

Question 46

what do mechanisms use ?

Answer 46

curly arrows

Question 47

what do curly arrows show ?

Answer 47

the movement of electrons

Question 48

what are the conditions if the reagant is NaOH ?

Answer 48

aqueous + warm

Question 49

what are the conditions if the reagant is KCN ?

Answer 49

ethanolic + warm

Question 50

what are the conditions if the reagant is NH3 ?

Answer 50

excess, concentrated ammonia dissolved with ethanol at a high pressure in a sealed container

Question 51

how many NH3 is needed in the nucleophilic substitution reaction ?

Answer 51

2

Question 52

what does NH3 act as ?

Answer 52

a base

Question 53

what are the products in the elimination reaction ?

Answer 53

an alkene potassium - halogen water

Question 54

what is the elimination reagant and conditions ?

Answer 54

reagant - KOH conditions - ethanolic + hot

Question 55

what occurs in elimination ?

Answer 55

a large molecule loses an atom or group of atoms

Question 56

what does the OH- nucleophile act as ? and why ?

Answer 56

acts as a base - because it accepts a proton (H+)

Question 57

test for alkenes ?

Answer 57

bromine water - changes from yellow to colourless

Question 58

which H does the OH- nucleophile only react with ?

Answer 58

the adjacent carbon to make water

Question 59

what does CFC stand for ?

Answer 59

chlorofluorocarbons

Question 60

what are CFC's ?

Answer 60

they are halogenoalkanes containing chlorine and fluorine but no hydrogen

Question 61

uses of CFC's ?

Answer 61

- solvents - refrigerants

Question 62

when the product breaks what happens to the CFC's ?

Answer 62

the CFC's rise up to the ozone layer

Question 63

what is the symbol for ozone ?

Answer 63

O3

Question 64

what does O3 decompose to make ? show the equation ?

Answer 64

oxygen 2O3 -> 3O2

Question 65

why is ozone important ?

Answer 65

ozone absorbs ultraviolet light which causes cancer in humans - life wouldn't have evolves without the ozone layer