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chemistry > module 4 > Flashcards

module 4 Flashcards

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1
Q

what are the uses of organic materials

A

domestic central heating

electrical generation

powering many forms of transport

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2
Q

define a hydrocarbon

A

compound containing carbon and hydrogen only

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3
Q

define a homologous series

A

family of compounds with similar chemical properties whose successive members differ by CH2

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4
Q

define a functional group

A

part of a molecule that is largely responsible for the molecule’s chemical properties

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5
Q

define an aliphatic compound

A

carbon joined together in straight or branched chains or non-aromatic rings

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6
Q

define an alicyclic compound

A

carbons joined together in ring structure

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7
Q

define an aromatic compound

A

carbons joined in a benzene ring

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8
Q

how are covalent bonds broken?

what is the difference between these two types. give definitions.

A

broken by homolytic or heterolytic fission

homolytic – each of the bonded atoms takes 1 of a shared pair of electrons (each atom has a single unpaired electron, so they become a radical

heterolytic – one of the bonding atoms takes both electrons from the bond
the ‘taker’ becomes a negative ion
the ‘bystander’ becomes a positive ion~

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9
Q

what do curly arrows show

A

movement of electron pairs

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10
Q

what are the three types of reaction

A

addition - 2 reactants form one product

substitution - atom/group of atoms(goa) replaced by different atom/goa

elimination - removal of a small molecule from a larger one
one reactant forms 2 products

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11
Q

what are the uses of alkanes

A

used as fuel

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12
Q

describe the formation of a sigma bond

A

result of the overlap of 2 orbitals (1 from each bonding atom)

sigma has 2 electrons shared between atoms

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13
Q

how does the length of the chains in an alkane affect the boiling point

A

as the chain length increases,
there are greater LDF,
so the boiling point increases

also, the surface area increases,
so there is more surface contact,
so there is more LDF

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14
Q

how does the presence of branches affect the boiling point

A

branched alkanes have less points of contact so they have less LDF

branches prevent molecules from getting close as straight chain molecules so there are less LDF

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15
Q

explain why alkanes have a low reactivity

A

C-C and C-H sigma bonds are strong

C-C non-polar

C-H electroneg. is similar so are considered non-polar

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16
Q

what conditions are required for radical substition

A

UV light and high temperature

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17
Q

how does the propagation step end in radical substitution?

A

when 2 radicals collide

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18
Q

what allows propagation to cycle into a chain reaction

A

radical produced in 2nd step

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19
Q

what are the limitations of free radical substitution

A

has problems that limit its importance for synthesis of one organic compound

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20
Q

what are the conditions required for a compound to have E/Z isomerism

A

molecule must have a C=C and different groups attached to each C in the C=C

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21
Q

what’s the difference between cis/trans and E/Z isomerism

A

in cis/trans isomerism, one of the attached groups on one carbon must also have the same group attached to the other carbon

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22
Q

give a brief synopsis on the cahn-ingold-prelog rules

A

atoms are given priority based on their atomic number

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23
Q

what happens if the 2 groups attached to the carbons have the same atomic number

A

group given a higher priority at the first point of difference in the group

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24
Q

describe the bonding in alkenes in terms of the double bonds

A

for each C of the double bond, 3 or 4 e- are used in 3 sigma bonds
(1 to other C, other 2 to 2 other atoms)

this leaves 1e- (in a p-orbital) on each C of the double bond

pi bond forms by the sideways overlap of 2 p-orbitals (1 from each carbon)

pi electron density concentrated above and below the plane

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25
Q

what makes the alkene and alkanes different in terms of movement

A

presence of pi bonds prevents rotation because it locked the carbon atoms of the double bond in position

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26
Q

explain the trigonal planar shape of the C in the double bond

A

3 regions of e- density around carbon

3 regions repel each other so it’s 120 degrees

atoms are in the same place

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27
Q

what makes the alkenes more reactive than alkanes

A

C=C

pi bond is outside of bond, so more exposed than e- in sigma bonds so the pi bond readily breaks more easily than sigma bond

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28
Q

what are the conditions required for hydrogenation

what type of reaction is it

A

nickel catalyst
423 K

addition

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29
Q

what are the conditions required for halogenation

what type of reaction is it

A

RTP

addition

30
Q

what are the conditions required for hydration

what type of reaction is it

A

steam
acid catalyst (phosphoric acid)

addition

31
Q

what allows electrophilic addition in alkenes

A

double bond

represents region of high electron density due to pi electrons

which attracts electrophiles

32
Q

define an electrophile

A

compound attracted to electron dense areas

accepts a electron pair

(example is a positive ion)

33
Q

how can non-polar molecules do electrophilic addition

A

pi electrons interact with electrons in X-X

polarisation of X-X forms induced dipole

electron pair of pi attracted to less electronegative X end

34
Q

order carbocations of their stability

what makes a carbocation stable

A

primary < secondary < tertiary

linked to electron-drawning ability of alkyl groups

each alkyl donates and pushes electrons towards positive charge of carbocation

positive charge spreads over alkyl

more alkyls allows charge to spread out more, making the ion more stable

35
Q

what are some characteristics of alcohols when compared to alkanes

A

lower volatility

higher melting point

higher water solubility

differences become smaller the higher the chain length

36
Q

compare the polarity and the intermolecular forces of alkanes and alcohols

A

in alkanes, C-H bonds have similiar electronegativity so are non-polar, thus have weak LDF

in alcohols, O-H are polar
electronegativity is different (so polar molecule)
the molecule has weak LDF and stronger hydrogen bonds between O-H groups

37
Q

explain alcohols low volatility

A

hydrogen bonds hold the molecules together

requiring more energy to overcome LDF in alkanes

thus alcohols have low volatility

38
Q

explain why solubility decreases as the chain length of alcohols increases

A

influence of the OH group decreases

39
Q

name the reactions of the alcohols

A

combustion

oxidation

dehydration

substitution

40
Q

what causes the change in color of the oxidising agent in oxidation of alcohols

A

reduction of dichromate (VI) ions –> chromium (III) ion

41
Q

give the molecular formula of the oxidising agent used in oxidation of alcohols

A

K2Cr2O7/H2SO4

42
Q

describe conditions for the dehydration of alcohols

A

heat under reflux
acid catalyst –> alkene

43
Q

describe the substitution reaction of an alchol

A

Hydrogen halide produced in reaction:
NaX + H2SO4 –> HX + NaHSO4

then:
alcohol + HX –> haloalkane + H20
reflux

44
Q

describe the conditions and reaction of an alkane becoming a haloalkane

A

radical substitution

UV light + halogen

45
Q

describe the oxidation of primary alcohol

A

distil –> aldehyde

reflux –> carboxylic acid

46
Q

describe the oxidation of secondary alcohol

A

reflux –> ketone

47
Q

what is dehydration of an alcohol an example of what type of reaction

A

elimination

48
Q

explain why the C-X bond in haloalkanes is polar

A

electronegativity difference

electron pair is closer to more electronegative halogen so the C-X is polar

49
Q

what allows nucleophilic substitution in haloalkanes

A

the C in the C-X is less electronegative so electron-deficient

which attracts nucleophiles

50
Q

what is used in nucleophilic substitution of haloalkanes

A

ethanol solvent

allows the (insoluble) haloalkane and the water to mix and produce a single layer

51
Q

what type of fission breaks the C-X bond in nucleophilic substitution

A

heterolytic fission

produces a X- (negative ion)

52
Q

how is the rate of hydrolysis measured

A

adding silver nitrate

Ag+ + X- form AgX precipitate

53
Q

the rate of hydrolysis increases as …

A

the strength of the C-X bond decreases

54
Q

how is plastic made and why

A

by polymers

cheap and polymers are unreactive

hard to dispose, which creates problems

55
Q

give an example of non-biodegradeable polymers

A

alene-based polymers

56
Q

what is the first way of disposing polymers

A

combustion for energy production

plastics are burnt so the chemical energy transferrs

but CO2 produced (greenhouse gas)

57
Q

what are the two another ways of disposing polymers

A

use as chemical feedstock for production

removal of toxic waste production
depending on the plastic, toxic gas produced

58
Q

which halide solution with silver is soluble in dilute and concentrated ammonia solution

A

AgCl – soluble in both

Agr – soluble in conc. ammonia solution

59
Q

describe the ozone layer

A

high conc. of ozone molecules in a layer of stratosphere which absorbs high proportion of UV radiation

is continually formed and broken down at the same rate

60
Q

what are the different types of UV and what is their different absorptions by ozone

A

UVa = 5% absorbed

UVb = 95% absorbed

UVc = 100% absorbed

61
Q

how does ozone depletion link to skin cancer

A

more UV reaches the earth’s surface

higher risk of skin cancer

62
Q

describe chloroflourocarbons

A

developed for use as refrigerants

low reactivity
high volatility
non-toxic

63
Q

how is the chlorine radical able to destroy ozone

A

1 chlorine radical destroys ~100,000 ozone molecules

64
Q

give the reaction for the breakdown of ozone with radicals

A

R. + O3 -> RO + O2
RO + O -> R + O2
O3 + O -> 2O2

65
Q

give the reaction for the breakdown of ozone with nitrogen monoxide

A

NO. + O3 -> NO2. + O2
NO2. + O -> NO. + O2
O3 + O -> 2O2

66
Q

describe the montreal protocol

A

effects of CFCs on ozone layer were established in 1970s

67
Q

what are some alternatives for CFCs

A

HCFC
Has C-H bond which degrades before it reaches the stratosphere

Hydrocarbons

68
Q

describe the greenhouse effect

A

electromagnetic radiation from sun reaches earth’s atmosphere

earth’s surface absorbs this and emits it as IR

greenhouse gases absorbs IR and some gases into space

earth’s atmosphere warms up

69
Q

what happens to molecules when they absorb IR

A

(cov) bonds vibrate more

70
Q

the greenhouse effect of a gas depends on …

A

conc. of it in atmosphere

its ability to absorb IR

71
Q

what is mass sprectrum used for

A

identify unknown compounds

determine abundance of an isotope of an element

gain more info on the structure of a molecule

chemistry (6 decks)

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