Elements From The Sea

Front 1

why is the sea so salty

Back 1

Cracks in the Earth‟s crust allow water to contact molten rock. Vast amounts of minerals aredissolved in the super heated water and these are released into the oceans via hydrothermalvents.

Front 2

why is the sea so salty

Back 2

Other salts come from the weathering of rock and eventually get washed into the sea.

Front 3

what happens as the sea water evaporates

Back 3

salts become more concentrated.

Front 4

where is the element bromine extracted from

Back 4

bromide ions found in sea water

Front 5

why does the Dead Sea in Israel contain the largest number of bromide ions

Back 5

salts are constantlywashed into it but cannot escape.

Front 6

how are ionic solids held together

Back 6

by the electrostatic attraction between the anions and cations.

Each positive ion (cation) exerts an attraction on several surroundingnegative ions (anions).The ions build up to form an ionic lattice.

Front 7

eg sodium chloride

Back 7

Each Na+ion has coordination number = 6 aseach Na+is surrounded by 6 Clions.Coordination number of Cl-= 6 as each Clisalso surrounded by 6 Na+ions.The attractive forces are stronger overall in thisstructure than repulsions.

Front 8

what happens when an ionic solid dissolves in water

Back 8

theions are surrounded by water molecules.

Front 9

why

Back 9

The -oxygens on water molecules areattracted to the positive ions and the + Hatoms in water are attracted to the negativeions

Front 10

what are ions surrounded by water molecules said to be?

Back 10

hydrated

Front 11

why do anions and cations behave independently when dissolved in water

Back 11

separated widely from each other

Front 12

what is sea water

Back 12

a mixture of positive and negative ions

Front 13

What are hydrated salts

Back 13

Some salts contain molecules of water packed into their lattices. This isshown in the formulae e.g CuSO4. 5H2O(s). The water in these salts is calledwater of crystallisation and the salts are said to be hydrated.

Front 14

what does strong heating of hydrated salts cause

Back 14

drive out this water to leave anhydrous salts.CuSO4. 5H2O(s) CuSO4 (s) + 5H2O(g)

Front 15

what is a precipitate

Back 15

2 types of ions coming together to form a solid (precipitate) that watermolecules cannot dissolve.

Front 16

What happens to the appearance of a solution with a precipitate

Back 16

The solid will sink to the bottom of the solution. Theappearance of the solid in solution will cause the liquid mixture to go from clear to cloudy untilall the solid has settled out.

Front 17

Are nitrates soluble

Back 17

yes, all are

Front 18

are Chlorides soluble

Back 18

All chlorides are soluble except AgCl, PbCl2

Front 19

Sulphates?

Back 19

Sulphates are soluble except BaSO4, PbSO4 , SrSO4

Front 20

Carbonates?

Back 20

Carbonates are insoluble except for NH4+and group 1 carbonates.

Front 21

sodium, potassium and ammonium salts?

Back 21

all are soluble

Front 22

What is a reducing agent?

Back 22

substance that provides electrons (= species oxidised inthe equation).

Front 23

What is an oxidising agent?

Back 23

Oxidising agent = substance that removes electrons (= species reduced inthe equation)

Front 24

What type of oxidation states do elements on its own have?

Back 24

0 eg O2 and Fe

Front 25

what are the oxidation states of simple ions

Back 25

charge on the ions

Front 26

what is the oxidation of Fluorine

Back 26

-1

Front 27

what is the oxidation state of O

Back 27

-2

(exceptionsare peroxides where it is –1, and F2O where it is +2)

Front 28

Oxidation number of hydrogen

Back 28

+1 (exceptions arecompounds with H and reactive metals e.g MgH2 or NaH where it is –1)

Front 29

Cl in compounds is

Back 29

–1 except in compounds with O or F

Front 30

what must the oxidation states in a neutral compound add up to

Back 30

0

Front 31

what must the oxidation states of molecular ions add up to

Back 31

overall charge of ion

Front 32

why are oxidation states in transition metals shown in the name

Back 32

Transition metals can show more than one oxidation state in compounds.

Front 33

what are oxyanions

Back 33

molecular ions with negative charge that contain oxygen andanother element. The oxidation state of the element joined to oxygen isshown in brackets after the name of the ion in Roman numerals. The ionname starts with part of the name of the element that is joined to oxygen andends in -ate. eg ClO3-chlorate (V

Front 34

when is an element oxidised

Back 34

oxidation state increases (becomes morepositive). (number of electrons decreases)

Front 35

when is an element reduced

Back 35

its oxidation state decreases (becomes morenegative).(number of electrons decreases)

Front 36

what is an oxidising agent

Back 36

element within a compound which causes oxidation (the element itself gets reduced)

Front 37

what is a reducing agent

Back 37

element within a compound which causes reduction (the element itself gets oxidised)

Front 38

how is the reducing agent or oxidising agent named

Back 38

as it's compound

Front 39

what happens if a question asks for the systematic name of an inorganic compound

Back 39

include oxidation states where appropriate

Front 40

how are halogen elements found

Back 40

diatomically

Front 41

what are the physical trends down the group?

Back 41

melting point and boiling points increase down the group

colour of compounds darkens down the group

Front 42

why do boiling and melting points increase down the group

Back 42

as the number ofelectrons (and thus size of atom and relative mass) in the non-polar molecules rises, leading to strongerinstantaneous dipole-induced dipole intermolecular bonds.

Front 43

what is fluorine like (F2)

Back 43

volatility= gas

reacts with water

soluble in organic solvents (hexane

pale yellow gas at rtp

Front 44

Cl2

Back 44

green gas at rtp

volatility=gas

slightly soluble with water to give pale green solution

with hexane is soluble to give pale green solution

Front 45

Br2

Back 45

dark red liquid at rtp

volatility=liquid, forms brown gas on warming

slightly soluble with water to grive red-brown solution

soluble with hexane to give red solution

Front 46

I2

Back 46

shiny blood-red solid at rtp

volatility=sublimes on warming to give a purple vapour

barely soluble with water to gives brown solution

soluble with hexane to give violet solution

Front 47

what is the solubility of halogen (non polar) molecules like

Back 47

dont dissolve easily in water (low solubility)

but are much more soluble in organic solvents

have low solubility in water as of covalent bonds

Front 48

what is the colour of chlorine in hexane like

Back 48

pale green

Front 49

bromine in hexane

Back 49

red

Front 50

iodine in hexane and water

Back 50

violet in hexane

brown in water

Front 51

how do halogens usually react

Back 51

by gaining an electron to form a noble gas configuration. This makes them oxidising agents

Front 52

what type of ions are halogens

Back 52

halide ions (eg Cl-)

Front 53

What happens to halogen's reactivity and oxidising power down the group

Back 53

decreases down the group

Front 54

what type of compunds do halogens form with metals

Back 54

ionic compounds

Front 55

what type of compounds do halogens form with other non metal compounds

Back 55

covalent bonds

Front 56

what are the oxidation states like in interhalogen compunds

Back 56

the more reactive halogen will be the -1oxidation state (the other will be in a positive oxidation state)

Front 57

what happens when halogens react in solutions

Back 57

a displacement reaction occurs

A more reactive halogen will displace the halide ions of a less reactivehalogen in solution.

Halide ions are oxidised, the halogen is reduced.

colour produced is of the diatomic halogen molecule produced

Front 58

what is electronegativity

Back 58

tendency of atom to attract a bonding pair of electrons

Front 59

why happens to electro-negativity down the group

Back 59

decreases

Front 60

why

Back 60

larger atoms attract less than smaller ones; as positive nucleus is further away and more shielded as number of shells increases

down group atoms become larger (more shells, blocking attraction of positive nucleus) so electronegativity decreases

Front 61

Chemical properties of halogens

Front 62

what happens to reactivity down the group

and strength as oxidising agents

Back 62

decreases

Front 63

why?

Back 63

The atoms get larger. The outer shell gets further from the nucleus. The attraction between the nucleus and electrons gets weaker, so an electron is less easily gained.

Front 64

how can you test for halide ions

Back 64

using silver nitrate solution (AgNO3)

Front 65

what happens when chloride ions react with silver ions

Back 65

white precipitate of silver chloride forms

Ag+(aq) + Cl-(aq) give AgCl(s)

Front 66

bromide ions and silver ions

Back 66

cream precipitate of silver bromide

Ag+(aq) + Br-(aq) AgBr(s

Front 67

iodide ions and silver ions

Back 67

Ag+(aq) + I-(aq) AgI(s)

A yellow precipitate of silver iodide

Front 68

what happens when silver bromide is decomposed by light

Back 68

forms metallic silver

This is the basis for most filmbased photographic processes.Silver chloride is decomposed the fastest by light, AgI does not decompose easily onexposure to light.

Front 69

what is the first ionisation enthalpy

Back 69

theenergy needed to remove 1electron from every atom in 1mole of isolated gaseous atoms ofthe element.X(g) to X+(g) + e -

NB element must be in gas state

Front 70

how can the existance of electron shells be proved

Back 70

by measuring the successiveionisation enthalpies of an element = energy needed to remove eachelectron in turn from an atom until there are none left.

Front 71

what is the second ionisation of sodium

Back 71

Na+(g) to Na2+(g) + e

Front 72

why is there a large jump in energy for the second ionisation enthalpy

Back 72

This isbecause the second electron is in the second shell (the first electron camefrom the 3rd shell).

Front 73

why does the second electron need more energy to be removed?

Back 73

It is in a shell (2nd) closer to the nucleus. It is being removed from an atom that already has a positive charge.

Fewer filled electron shells between this e- and the nucleus so lessshielding from the attraction of the nucleus. (The first electron isshielded by 2 full inner shells)

Front 74

what are the large energy jumps evidence for

Back 74

existance of shells

Front 75

where do electrons exist

Back 75

in shells, designated n=1, n=2,

the further away a shell from the nucleus, the larger the n number

Front 76

what are these shells divided into

Back 76

sub shells

s, p, d, f

Front 77

how are sub shells further divided

Back 77

into atomic orbitals

each atomic orbital can hold a maximum of two electrons. These two electrons must have opposite (or paired) spins

Front 78

description of s sub shell

Back 78

1 orbital

hold max number of 2 elesctron

Front 79

description of p sub shell

Back 79

3 orbitals

hold max number of 6 electrons

dumbell shape

Front 80

description of d sub shell

Back 80

5 orbitals

hold max number of 10 electrons

Front 81

what is electronic configuration

Back 81

arrangement of electrons in orbitals

Front 82

how are orbitals filled?

Back 82

in orbitals of increasing energy

Front 83

how are orbitals filled up (when there is more than 1 orbital at the same energy)

Back 83

orbitals are first occupied singly by electrons

then when each orbital is occupied singly by electrons, electrons then pair up

Front 84

what tpe of spin do singly occupied orbitals have

Back 84

parallel spins

Front 85

what type of spin do electrons in doubly paired orbitals have

Back 85

opposite spins

Front 86

why does the 4s orbitall fill up before the 3d orbital?

Back 86

has a lower energy

Front 87

what do arrows in boxes represent

Back 87

arrows represent electrons

box represents orbital

arrows pointing in opposite directions have paired (opposite) spins

Front 88

what type of electronic configuration does chromium have

Back 88

1s2, 2s2, 2p6, 3s2, 3p6,3d5,4s1

Front 89

what type of electronic configuration does copper have

Back 89

1s2, 2s2, 2p6, 3s2, 3p6, 3d10,4s1

Front 90

Why are chromiu and copper exceptions?

Back 90

These exceptions are due to the high stability of a full or half filled d sub-shell and thereduction of repulsion between electrons that would have otherwise been paired in the 4s.

Front 91

Why are group 1 and 2 elements known as s block elements

Back 91

as have two electrons in their outermost sub shell, which is an s orbital

Front 92

why are groups 3,4,5,6,7 and 0 elements known as p block elements

Back 92

as contain 3,4,5,6,7, or 8 electrons in outer most sub shells which are in the p orbitals

Front 93

why are the first transition block elements know as d block elements

Back 93

as have electrons which fill d sub shell

Front 94

what do first ionisation enthalpies of group 1,2 and 3 elements provide evidence for?

Back 94

sub shells

Front 95

why?

Back 95

E.g small dips between Beand B, also Mg and Al as go from s to psubshells.

Also dips N to O, P to S are evidence of p3going to p4and electrons having to pair inorbitals leading to repulsion and a slightdrop in ionisation enthalpy as a result.

Front 96

what is the first step for manufacturing bromine from sea water

Back 96

acidified seawater withhigh Br ionconcentrationhas chlorineand steamadded to it.

Front 97

2

Back 97

The Cl2oxidises Br ionsto Br2.

A displacement reaction Cl2(aq) + 2Br-(aq) to Br2(aq) + 2Cl-(aq)

Steam evaporates the Br2 from the water with a little unreacted Cl2

Front 98

3

Back 98

A condenser cools the mixture and bromine and steam liquefy. Liquidbromine and water mix very poorly so most of the water is separated and returned tothe steaming process

Front 99

4

Back 99

Damp bromine (with a little dissolved Cl2) is distilled. The chlorine boilsout and is reused to react with fresh sea water

Front 100

5

Back 100

Last traces of water are removed from the bromine using ConcentratedSulfuric acid as a drying agent.

Br2(l) + H2O(l) + 98% H2SO4(l) to Br2(l) + dilute H2SO4 (aq)

Front 101

what is feedstock

Back 101

industrial term for chemical reactants

Front 102

what are the typical sequences in a chemical process

Front 103

what are the two main ways chemical processes can be carried out

Back 103

batch

continuous

Front 104

What is the batch process

Back 104

Reactants mixed in reaction vessel,

reaction is carried out

and products removed when reaction is complete.

Process then repeated withnext “batch” of reactants.

Front 105

What is the continuous process

Back 105

reactants constantly fed in at one end of the plantand products constantly removed at other end.

The processing does not stop.

Front 106

pros of batch process

Back 106

Better %conversion in agiven time thancontinuous

Versatile: severaldifferent reactions canbe carried out using thesame reaction vessel.

Plant cheaper:Equipment = largelygeneral purposevessels –can be boughtoff the shelf.

Most cost effectivewhen smallamounts of productneeded or for slowreactions

Front 107

cons of batch process

Back 107

More difficult tocontrol the releaseof heat (exothermicreactions)

Larger workforceneeded

More time wasted.If a new process isbeing done in the samevessel, time will be lostcleaning out the vesselcarefully to avoidcontamination.

Contamination more likely

Front 108

pros of continuous process

Back 108

Best for making ahigh tonnage ofjust one product.

Minimal labourrequired. (may notshut down for severalyears)

Safer. Avoids theneed to have largeamounts of reactants inone place so easier toremove heat

More easilyautomated. (Manyparts of the processcan be run by machine–reliable, less labourcost)

Front 109

cons of comtinous process

Back 109

Specially designedplant needed. Oftenvery difficult to adapt itfor other purposes.

Initial capital costmuch higher. Settingup specialised plant isvery costly.

Only cost effectiveif running at fullcapacity. (productmust be in constantdemand).

High contaminationrisk if used to makemore than 1product. Extensive,specialised machinerymuch harder to clean thana single open-shutreaction vessel.

Front 110

what must materials used to construct plants be like

Back 110

Materials used to construct the plant must not react with reactants, productsor catalysts. (Often glass ,special alloy or glass reinforced linings used instead of steel)

Front 111

how may feedstocks be prepared before reactions take place

Back 111

Purification

Getting the feedstocks into the correct ratio of quantities for the reaction.

Converting feedstocks into a state that allows them to be easily handled. (e.ggases or liquids best as can be pumped or piped around easily. Solids are costly to move about so theymay be either melted or mixed with a liquid and pumped as a “slurry”).

Front 112

where are inorganic feedstocks usually obtained from

Back 112

ores, minerals, sea water or the air.

Front 113

where do organic feedstocks come from

Back 113

Cracking of natural gas produces ethene and propene. Distillation of crude oil produces a range of fractions. Cracking producesalkenes. Reforming “naptha” fraction gives aromatic hydrocarbons, branchedalkanes and cycloalkanes( the majority of these are used in unleaded petrol

Front 114

what is co product

Back 114

when a process produces more than 1 useful product. The processmay become uneconomical if demand for one of these products falls.

Front 115

what is by product

Back 115

non-useful additional products, often made from side reactions.A lot of effort is put into minimising side reactions as far as possible.It is important to make the best use of both co- and by- products.

Front 116

how long does it take to pay off initial setting up costs

Back 116

several yearsbefore the sale of products actually balances all these costs and gives anoverall profit

Front 117

what are the two types of costs

Back 117

fixed costs

variable cost

Front 118

what are fixed costs

Back 118

these are independent of the amount of product made.e.g : land purchase, wages, and the capital costs of setting up the plantand surrounding infra structure

Front 119

variable costs

Back 119

relate directly to the amount of product made.e.g raw materials, transport of product, waste treatment.

Front 120

what is efficiency

Back 120

the best combination of pressure, temperature and rate of mixingavailable must be used

Front 121

pros and cons of high temps and pressure

Back 121

need more expensive plant

, usemore energy

can make reactions more difficult to control

but dogive a very high rate

Front 122

efficiency in equilibrium processes

Back 122

conditions for the bestyield of products must be considered.

A compromise temperature and pressure is often necessary which givesthe best balance of yield and rate.An effective catalyst (if available) greatly reduces costs.

Front 123

how are processes made as effcient as possible to maximise profit?

Back 123

-finding / using the optimum conditions for the process.

-using suitable catalysts.

recycling unreacted feedstock - separate it from products and send it back tothe reactor. effective insulation of piping etc. to reduce energy losses.

heat exchangers - use heat released in exothermic parts of theprocess to provide energy for endothermic processes (this may includeproviding hot water and central heating for the factory). The heat is often transferredas heated steam/water around the plant.

Front 124

where are most plants located

Back 124

good communications network (i.e easily reached by road, rail or water. Many bulk materials transported bysea).

supply of skilled labour in the area. plenty of water available.

waste disposal and treatment areas being available.

flat, firm land with room for expansion.

Front 125

what do strict safety laws require

Back 125

Strict health and safety reviews at all planning stages.

Rigorous risk assessments carried out.

Special health and safety responsibilities for some employees.

Frequent emergency practice drills.

Front 126

what are the principles of green chemistry

Back 126

Minimise waste (recycling or finding uses for waste products)

Reduce energy consumption (catalysts to reduce temperature,increasing atom economy). Reduce feedstock consumption (e.g reduce number of steps in aprocess)

Front 127

what do laws require for waste disposal

Back 127

must be environmental friendly

e.g waste added to rivers must be first adjusted for temperature, pHand heavy metal content and its effect on the dissolved oxygen contentof water must be negligible.

SO2 from the roasting of ores is converted into H2SO4 in neighbouring factories. The acid can be sold atprofit.Gases containing contaminants can be passed through solutions that remove contaminants –“scrubbers”. E.g NaOH(aq) can scrub air clean of bromine vapour.

Front 128

how do you calculate precentage yield

Back 128

actual moles of product

divided by x100

Expected moles of product

Front 129

how do you calculate atom economy

Back 129

relative formula mass of useful product

divide by x100

relative formula mass of all reactants used

To get a better idea of waste we use atom economy

Front 130

how can chlorine be manufactured

Back 130

Chlorine can be produced by the electrolysis of concentrated solutions ofsodium chloride (“brine”) NaCl.

Front 131

what are the two methods of manufacturing chlorine

Back 131

mercury cell

membrane cell

Front 132

what are cathodes and annodes

Back 132

cathodes are negatively charged

annodes are positively charge

Front 133

what is happening to the mercury cell process

Back 133

Uses a mercury cathode and is being phased out because of the amount oftoxic mercury lost into the environment.

Front 134

how is chlorine manufactured in the membrane cell 1

Back 134

an electric current is passed through a concentrated solution of sodium chloride

Front 135

2

Back 135

A membrane separates the solutionaround the anode and cathode.

Membrane made of PTFE (Teflon) so heatresistant and inert. Negative side chains addedto PTFE allow positive ions to pass through but repel negative Clions.

Front 136

3

Back 136

Na+ ions hydrated with water can passthrough the membrane but ClandOHcannotpass through.Also H2 and Cl2 don‟t get the chance tomix (explosive if they do).

Front 137

4

Back 137

The result is sodium hydroxide and hydrogen gas are formed at thecathode (= negative electrode) and Cl2(g) is formed at the anode (positiveelectrode). These are valuable co-products

Front 138

what are the equations

Back 138

Anode: 2Cl-(aq) to Cl2 (g) +2e-

Cathode: 2H2O (l) + 2e- to H2 (g) + 2OH-(aq)Oxidation Cl –1to 0

Reduction H +1 to 0

Overall equation:2Cl-(aq) + 2H2O(l) Cl2(g) + H2(g) + 2OH-(aq)

Front 139

what are advantages of membrane cells over mercury cells

Back 139

Lower running costs

Replacing mercury cells with membrane cells of same size producesmore chlorine.

No expensive treatment to remove toxic waste products needed.

Less environmental pollution

Front 140

what is the bond polarity like in covalent bonds such as O=O

Back 140

covalent bonds are a shared pair of electrons

in eg O=O and H-H

bonding electrons shared equally

Front 141

What happens If the atoms sharing the bonding electrons are different

Back 141

one nucleusmay attract the bonding electrons more strongly than another.

Front 142

what is electro negativity

Back 142

Electronegativity is a measure of an atom‟s attraction for bonding electrons.The higher the electronegativity value the more strongly that atom will attractbonding electrons.

Front 143

what are The most electronegative elements in decreasing value

Back 143

F,O,Cl,N

Front 144

what are the least electronegative elements

Back 144

elements are the metals in the bottom of group 1.

Front 145

what is the electronegativity like in H-F

Back 145

there is a significant difference in electronegativity.

This means the more electronegative F has a greater share of the bondingelectrons.

The greater electron density around F causes it to become slightly negativelycharged (“delta negative”

. The H has lost some its share of the bondingelectrons so becomes slightly positive in charge (“delta positive”

Front 146

what are polar bonds

Back 146

Bonds where there is a significant electronegativity difference

Front 147

what happens the difference in electronegativity becomes large enough

Back 147

forms an ionic bond

(where the bonding electrons stay on the negative ion

so non metals and metals...

Front 148

what are C-H bonds like?

Back 148

effectively non polar

Front 149

what are C-C bonds like?

Back 149

completely non polar

Front 150

what must substances have if they are in solid or liquid state?

Back 150

forces between particles holding them together

Front 151

what are intermolecular bonds

Back 151

bonds between molecules

Front 152

what are intermolecular bonds like if substances have high melting or boiling points

Back 152

strong asmore energy will have to be put in to overcomeintermolecular bonds to separate molecules

boiling involves breaking all the intermolecular bonds

Front 153

are instantaneous dipoles induced dipoles present in all substances

Back 153

yes

Front 154

how do idid bonds form 1

Back 154

Electrons inside a molecule (or noblegas atoms) are constantly moving randomly

Front 155

2

Back 155

Electron movements createuneven distribution of charge (instantaneous dipole).

E.g sometimesthere is more electron density on one side of a molecule making that molecule (briefly)slightly negatively charged (δ-).

Front 156

3

Back 156

A dipole is induced in a neighbouringmolecule creating an attraction.

Front 157

4

Back 157

this is an id id attraction

id id attractions are the weakest type of intermolecular bond

Front 158

why are id id interactions continusously forming and breaking

Back 158

as electron cloud is continuously moving

Front 159

when does an idid bond increase

Back 159

atomic mass gets larger (more electrons & outer electrons moreloosely held)

Molecules get larger (as molecular mass rises, more electronsagain).

The area of contact between molecules rises e.g a straight chainC5H12 pentane will have astronger intermolecular bondthan its branched chain isomer2,2-dimethylpropane. Thepentane molecules‟ straightchains can pack closertogether than chains in thebranch chained isomer.

Front 160

why do idid forces increase as carbon chains get longer

Back 160

more molecular surface area

so more electrons to interact

so as molecules get longer it takes more energy to overcome idid forces and seperate (why polyethene) is solid at room temp

Front 161

why are idid forces weak in branched chain (alkanes)

Back 161

branched chain (alkanes) cant pack closely together and have smaller molecular surface areas, so idid forces reduced

Front 162

when are pd pd dipoles created

Back 162

significant electronegativity difference betweenatoms bonded together causing bonding electronsto be shared unevenly.

slightly positively charged end of molecule attracts slightly negatively charged end of next molecule, and an intermolecular bond occurs

Front 163

strength of bonding

Back 163

hydrogen bonding

then pdpd

the idid

(pdpd bonds responsible for holding polyester together)

Front 164

what also affects pd pd bonding

Back 164

shape of the molecule

In some molecules (e.g CCl4) symmetrical dipoles cancel out each other‟seffects and the molecule is non-polar overall

Front 165

how is fluorin made as needed (in situ)

Back 165

it is very reactive, too reactive to store

made by electrolysing liquid hydrgoen fluoride

Front 166

how is chlorine transported

Back 166

by rail or road tanker as liquid

it is a higly toxic gas

Front 167

how is bromine transported

Back 167

in lead lined steal tanks supported in strong metal frames

Front 168

how are transport routes planned

Back 168

to minimise accident risk

Front 169

uses of fluorine

Back 169

Used to make the plastic polytetrafluoroethene (PTFE or “teflon”),

usedin non-stick coatings on cookware.

HCFC‟s used in air conditioning and refrigeration.

sodium fluoride used in toothpaste.

Front 170

risks of using flourine

Back 170

element itself is highly reactive and handling must be kept to a minimum

Front 171

uses of chlorien

Back 171

is an importnat intermediate in the manufacture of HCl and chlorinated solvents

used in plastic industry (PVC and polurethanes)

used in water treatmennt to kill pesticides

medicine

bleach 2NaOH + Cl2 NaCl + NaClO + H2O

Front 172

risks of chlorine

Back 172

pesticides can accumulate in the environment

CFC destroy stratospheric ozone

Front 173

uses of bromine

Back 173

used in flame retardent manufacturing

agricultural fumigants and in photography

Front 174

risks of bromine

Back 174

organic bromine compounds can destroy stratospheric ozone

Front 175

uses of iodine

Back 175

used in antiseptics, germicides and dyes

iodine 131 is used to diagnose thyroid disease

Front 176

further risks of bromine

Back 176

volatile liquid that is toxic by inhalation and burns on skin contact.

precautions included as mentioned above and

Sensors detect any leakage immediately.

Air contaminated with Br2 is passed through an alkaline “scrubbing” solution” toprevent Br2 escaping into the atmosphere.

2NaOH(aq) + Br2(g) to NaBr(aq) + NaBrO(aq) +H2O(l) all fairly non-hazardous products. Transported in lead lined steel tanks (lead does not react with Br2, steel does. Outersteel is needed for strength

Front 177

what happens when you electrolyse a solution containing iodide or bromide ions?

Back 177

halogen element is released at annode (halide ions lose electrons to annode, and are oxidised

at cathode, hydrogen ions from water forms hydrogen gas

Front 178

what are halogenalkanes

Back 178

= hydrocarbon chains in which one or more H‟s are replaced with halogenatoms.

homologous series : R-Hal

Front 179

naming haloalkanes

Back 179

alkane chain name is prefixed with halogen name

halogens listed in alphabetical order (bromo, chloro, fluoro, iodo)

with numbers indicating ppositin

and (di, tri, tetra, penta)

numbering to give lowest number total overall

Front 180

what type of bond is a carbon halogen bond?

Back 180

polar, but polarity is not high enough to allow them to dissolve in water

Front 181

what happens to boiling point of haloalkanes as you go down the group?

Back 181

inreases.

atomic number increases,

number of electrons increases

stronger id id forces

more energy needed to overcome forces

Front 182

why do boiling points increase as length of carbon chain increases?

Back 182

stronger idid forces, more electrons

Front 183

why does boiling point increase when number of halogens on chain rises

Back 183

more electrons, so stronger idid forces

Front 184

what happens to bond enthaply as size of halogen increases?

Back 184

bond strength decreases

Front 185

what happens to reactivity down the group?

Back 185

increases

Front 186

what happens to bond polarity down the group

Back 186

decrease (ie C-F, is more polar than C-I)

Front 187

what do these trends show

Back 187

that it is bond strength rather than bond polarity which has the greatest effect on the reactivity of haloalkanes

(bromo and iodo compounds are reactive and so are useful as chemical intermediates in chemical synthesis)

Front 188

what type of reaction occurs when haloalkanes reach the stratosphere (eg CFCs)

Back 188

undergo homolytic fission

these involve the breaking of the C-halogen bond.

In the atmosphere, UV radiation of the correct energy breaks these bonds byhomolytic fission

Front 189

what happens in heterolytic fission of R-Hal bond

Back 189

CH3Cl to CH3+ + Cl-= heterolytic fission of chloromethane.The halogen leaves with both bonding electrons to become a halide ion.The carbon is left with a positive charge. An ion with a positively charged carbon is called acarbocation. CH3+is an example of a carbocation- covered in Polymer revolution PR laterHeterolytic reactions are most likely to happen in polar solvents where radiation is not involved. )

Front 190

why can nucleophilic substitution occur in haloalkanes

Back 190

carbon to which the halogen is joined has a slight positive charge due tothe polarity of the C-halogen bond.

This means that the carbon joined to the halogen can be attacked bynucleophiles.

Front 191

what is a nucleophile?

Back 191

atom/ ion/ molecule that can donate a lone pair ofelectrons to a positively charged carbon atom to form a new covalentbond.

Front 192

what happens when haloalkanes undergo nucleophilic substitution?

Back 192

nucleophile takes the placeof the halogen (substitution) whichleaves as a halide ion.

Front 193

what do curly arrows show

Back 193

show the movement of a pair ofelectrons

Front 194

Explain what happens

Back 194

nucleophile attacks partially positive (δ+) carbonattached to halogen.

causes C-Halogen bond to break. Both electrons from C-Hal bond goto the halogen atom which becomes the halide ion (Hal-).

R-Hal + Nu- to R-Nu + Hal-

Front 195

where do you draw the arrows?

Back 195

curly arrow showing bond breaking starts in the middle of the bond andfinishes on the halogen atom.

curly arrow from the nucleophile starts from the lone pair and finishes at theδ+ carbon.

Front 196

what are reagents

Back 196

chemical(s) added to cause a desired reaction.

Front 197

hydrolysis, reagents, conditions and reaction

Back 197

Reagent: Aqueous sodium hydroxideConditions: Heat under reflux (ethanol may be added as a co-solvent).

Reaction: R-Hal + OH-(aq) R-OH + Hal-

Front 198

hydrolysis using water

Back 198

Here the reaction occurs in two stages as the water needs tolose a proton (H+) after attackto restore the normal numberof two bonds for oxygen.

reaction for water: R-Hal + H2O R-OH + H+ + Hal

Front 199

why is this reaction with water slower for making alcohols than the other

Back 199

this reaction with water is a much slower way to make an alcohol. The negativelycharged hydroxide ion used in the alkaline hydrolysis will react much faster than the neutralwater molecule, plus only one step is involved in the hydroxide reaction.

Front 200

reaction with ammonia

Back 200

Reagent: Concentrated aqueous ammoniaConditions: Heat in a sealed tube!

R-Hal + NH3 R-NH2 + H+ + Hal

reaction takes place in two stages as aproton (H+) must be lost to restore nitrogen‟s usual number of 3 bonds

Front 201

how can you make a haloalkane?

Back 201

reaction of an alcohol with suitable halide ions in the presenceof a strong acid:

e.g Chloroalkanes made from suitable alcohol and conc. HCl Bromoalkanes made from suitable alcohol and a mix of sodium bromide andconc.sulphuric acid.

Conditions: Heat under Reflux

Front 202

what happens?

Back 202

Reaction between the alcohol andthe conc.acid adds a proton onto theO of the OH group.

halide ion acts as nucleophile andpushes off a molecule of water.

The halogenoalkane and water areimmiscible so a separating funnelcan be used to separate them.

Sodium hydrogencarbonateNaHCO3 is used to remove acidicimpurities. (neutralises them to form a sodium salt, water and carbon dioxide)

Front 203

what are drying agents?

Back 203

used to remove the last traces of water.Good dryingagents = anhydrous sodium sulphate (or Anhydrous calcium chloride)

Front 204

what are titrations?

Back 204

a method of quantitatively finding concetration of a solution by reacting a known volume of soultion with another solution of known concentration

Front 205

how is the end point of reaction detected

Back 205

by adding an indicator

eg phenolphthalein red to colourless (when adding acid to alkaline, acid base reaction

or methyl orange(yellow in akali/ red in acid

Front 206

why dont you use universal indicator

Back 206

colour change is too slow; want indicators that change colours quickly in small pH range

Front 207

1st step

Back 207

a fixed volume os solution of unkown concentrstion is placed into a conicle flask using a pipete

Front 208

2

Back 208

a few drops of suitable indicator are addedand the mixture placed on a white tile, to see end point more clearly

Front 209

3

Back 209

soltion of known concentration is added slowly from burette with constant swirling

Front 210

4

Back 210

as you approach end point add solution from buretter drop wise

Front 211

5

Back 211

after a rough titration, accurate titrations followed until concordant results obtained

Front 212

how do you calculate concentration

Back 212

c=n/v

c=moldm to the -3

n=amount of substance in moles

v=volume of solution in dm cubed

Front 213

how do you use a seperating funnel and why?

Back 213

Used to separate 2 liquids which are immiscible (don‟t mix with each other). Open tap to let the bottom liquid flow out . Close the tap just as the top liquid reaches the tap.(Stopper is only put on when shaking contents)

Front 214

what is refluxing

Back 214

Lets you keep a volatile liquid at boiling point for a longtime without evaporation losses. Condenser is mounted vertically. As liquid in flask boils, the vapour rises up into thecondenser Condenser cools vapour back into a liquid. Liquid drips back into the reaction flask and isheated again.

Front 215

what is the good use of the co products of the electrolysis method for making chlorine?

Back 215

hydrogen and chlorine to make hydrogen chloride.H2 + Cl2 2HClHCl(g) is dissolved in water to create concentrated hydrochloric acid. Transporting inconcentrated form is most economical (can be diluted later).Making PVC also produces HCl(g), so hydrochloric acid can be a useful co-product of thistoo.

Front 216

how are Many organic halogen compounds found

Back 216

naturally occurring in the oceans.

These undergo hydrolysis reactions with water and sometimes radical substitution (see Aand PR for details of how these happen) such as 2CH3Cl + I2 + hv 2CH3I + Cl2 - note thisis not an easily predictable displacement – UV/ visible radiation usually needed for thesereactions