Chemistry Form 6 Sem 2 06

8/13/2019 Chemistry Form 6 Sem 2 06

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Element Chlorine, Cl2 Bromine, Br2 Iodine, I2

Atomic radius (nm) 0.099 0.114 0.133

Physical state at

room temperatureElectronic

configuration

o - - --

Yellow greenish

gas

Red brown

liquid

Black

solid3s2 3p5 4s2 4p5 5s2 5p5

.

Boiling point (oC) -34.5 58.6 184

Bond energy

(kJ/mol)242.5 191.5 150.0

Electron affinity(kJ/mol)

-364 -340 -297

Electronegativity 3.0 2.8 2.5

Solubility in water soluble Sparingly solublesoluble


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1. A

17, .

, G 17, , . A , , . A

,

2. , , ,

A G 17 , , , , F2,C2,B2,I2, A2

, , . C , , .

G 17


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A G 17, C2 B2 I2

D ' . A , G G 17, .

A , , ,

, , . . , G 17,

.


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3. E,

E .

E 17 .

F G 17. G 17

.

2 .

E : C C () 2 C () H = + 242.5 1

,

. A , , .


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F , FF , .(

).E

.

E : F () + F () HEA= 364 1

G 17 17. , ,

. A , ,


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4.

G 17.F G 17 . F,

.

B

( ), .

E : C2() + H2 () HC () + HC ()

B2() + H2 () HB () + HB ()I

(I) I

3

.

E :I2 () + I () I3

()


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. ,

. H .

2 HOCl 2 HCl (aq) + O2 (g)

Overall : 2 Cl2 + 2 H2O 4 HCl (aq) + O2 (g)

bleaching

, , CC4, .

Halogen Chlorine, Cl2 Bromine, Br2 Iodine, I2

Colour in aqueous

solutionPale yellow Brown Brown

Colour in organic

solvent (CCl4) Colourless Brown Purple


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6.2 C G 17

H .

F2 () + F () E = + 2.87

C2 () + C () E = + 1.36

B2 () + B () E = + 1.07

I2 () + I () E = + 0.54

A .

, .


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Observation Equation

Chlorine in

Tetrachloromethane

is added to aqueouspotassium bromide

(KBr).

Colourless solution

in CCl4 turnedbrown

Reactants : Cl2 + Br-

So the half equation for reaction:

Cl2 + 2e- 2 Cl- E0 = + 1.36 V

2 Br- Br2 + 2e- E0 = - 1.07 V

--------------------------------------------Cl2 + 2 Br

- 2 Cl- + Br2Ecell = + 0.29 V

Since the Ecell is positive, the

Bromine in

tetrachloromethaneis added to aqueous

potassium iodide

(KI)

reaction is spontaneous.

Brown colour inCCl4 turn purple

colour.

Reactants : Br2 + I-


Br2 + 2e- 2 Br- E0 = +1.07 V

2 I- I2 + 2e- E0 = - 0.54 V--------------------------------------------

Br2 + 2 I- 2 Br- + I2

Ecell = + 0.53 V

Since the Ecell is positive, thereaction is spontaneous.


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Iodine is

tetrachloromethane

is added to aqueous

Purple colour in

CCl4 remain

Reactants : I2 + Cl-


I2 + 2e- 2 I- E0 = + 0.54 V2 Cl- Cl2 + 2e

- E0 = - 1.36 V

--------------------------------------------

I2 + 2 Cl- 2 I- + Cl2

(KCl)

Ecell = 0.82 VSince the Ecell is negative, the

reaction is non-spontaneous.


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5.2.1 C (II) (III)

G (II) (III)

. F3+ () + F2+ () E = + 0.77

I (II) , F2+,

C (II) .Reactants : Cl2 + Fe

2+ ; So the half equation for reaction:

Cl2 + 2e- 2 Cl- E0 = + 1.36 V

Fe2+ Fe3+ + e- E0 = 0.77 V

B (II) .

2

+ e - + ecell

= + .

Since the Ecell is positive, the reaction is spontaneous.

Obs : pale yellow solution dissolve in green solution to form yellow solution

Reactants : Br2 + Fe2+

; So the half equation for reaction:Br2 + 2e- 2 Br- E0 = + 1.07 V

Fe2+ Fe3+ + e- E0 = 0.77 V

Br2 + 2 Fe2+ 2 Br- + 2 Fe3+ Ecell = + 0.30 V

Since the Ecell is positive, the reaction is spontaneous.

Obs : brown solution first dissolve in green solution and form yellow

solution


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I (II) .

Reactants : I2 + Fe2+ ; So the half equation for reaction:

I2 + 2e- 2 I- E0 = + 0.54 V

Fe2+ Fe3+ + e- E0 = 0.77 V

I2 + 2 Fe2+ 2 I- + 2 Fe3+ Ecell = 0.23 V

Since the Ecell is negative, the reaction is non-spontaneous.

Obs : no changes occur*Conversely when iron (III) ion is added to iodide ion,

2 I- + 2 Fe3+ I2 + 2 Fe2+ Ecell = + 0.23 V

iodide ion (which act as reducing agent) are able to reduce iron (III) ion to

I

..

form iron (II) ion and iodine is formed.

Chlorine and bromine can act as oxidising agent while iodine is not

a good oxidising agent. Conversely, iodide ion can act as a goodreducing agent.


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, 232, .

,

(232

) . ,

, , sulphate ion, SO4

2-

S2O32- + 5 H2O 2 SO4

2- + 8 e + 10 H+

Cl2 + 2 e 2 Cl

--------------------------------------------------------------------

B ,

. , 46

2,

2 3

- +2

+2

4

- + +

2 S2O32- S4O62- + 2 eI2 + 2 e

2 I

---------------------------------------

2 S2O32- + l2 S4O6

2- + 2 l


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Example : The carbon monoxide in a sample of polluted air can readily be

determined by passing it over solid iodine(V) oxide, I2O5, to give carbon dioxide and

iodine.(a) Write a balanced equation reaction between carbon monoxide and iodine(V) oxide.

............................................................................................................................................

(b) The iodine produced is removed and titrated with aqueous sodium thiosulphate:

2 Na2S2O3 (aq) + I2 (s) Na2S4O6 (aq) + 2 NaI (aq)

A 1.0 dm3 sample of air produced iodine that required 20.0 cm3 of 0.10 mol dm-3

sodium thiosulphate to discharge the iodine colour. Calculate the mass of carbon

I2O5 + 5 CO 5 CO2 + I2

monoxide in this sample of polluted air. [4]Mol of Na2S2O3 = MV / 1000 ; mol = (0.10)(20.0) / 1000

Mol of Na2S2O3 = 0.002 mol

From eq (b) since 2 mol of Na2S2O3 = 1 mol of I2

Mol of I2 = 0.001 molIn (a) since 1 mol of I2 = 5 mol of CO

Mol of CO = 0.005 mol

Mass of CO = mol x RMM @ mass = 0.005 x (12.0 + 16.0)

Mass of CO = 0.14 g


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, () ( ).

E :C2 () + H2() 2 HC ()

Halides HF HCl HBr HI

Boiling point (oC) 23 - 85 - 66 - 35

Bonding enthalpy (kJ/mol) +560 +433 +366 +298

G 17 ( E0) 2000C

, , 450C


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A , ,

. H HF ,

D HC, HB HI. HC < HB < HI,

, .

G 17.

. G 17, . A , ,

H . ,

. .

E : 2 H () H2 () + 2()


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. , HF


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5.3.1 D

, () + H24() H () + H4()

, , ( ) , .

H

2 H2SO4 (aq) + CaF2 (s) Ca(HSO4)2 (s) + 2HF (aq)

.E :

NaCl (s) + H2SO4 (aq) HCl (g) + NaHSO4 (aq)


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H

, .

F ;

NaBr (s) + H2SO4 (aq) HBr (g) + NaHSO4 (aq)

2 HBr (g) + H2SO4 (aq) Br2 (l) + SO2 (g) + 2 H2O (l)Observation : brown liquid is formed around the test tube, and a

colourless pungent gas evolved which turn blue litmus to red.

F ;NaI (s) + H2SO4 (aq) HI (g) + NaHSO4 (aq)

8 HI (g) + H2SO4 (aq) 4 I2 (l) + H2S (g) + 4 H2O (l)Observation : black spot is formed on the wall of the tube. A bad egg

smell gas evolved from the mixture.


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6.3.2 H

I ,

(III) ,

E : 4() + 6 2() 4 3() B I

H, , , C . A

, B5 , I5,

B (III) (III) .

B3 () + 3 H2 ()

I3 () + 3 H2 ()

, H33,

3 HBr (aq) + H3PO3

3 HI (aq) + H3PO3


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A ( )

I , 6

ChemicalHydrochloric

acidChlorine

Hypochlorous

acid

Chlorous

acid

Chlorite

acid

Perchlorite

acid

Formula HCl Cl2 HClO HClO2 HClO3 HClO4

, . A .

state + + + +

oxoacid


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HClO

(Hypochlorous acid)

HClO2(Chlorous acid)

HClO3(chloric acid)

HClO4(Perchloric acid)

HClO + H2O

ClO+ H3O+

HClO2 + H2O

ClO2+ H3O

+

HClO3 + H2O

ClO3+ H3O

+

HClO4 + H2O

ClO4+ H3O

+

A


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A . , H ( ) . A , .

. E : HI HB HI3

HB3.

electronegative

increase

.

.

.

compare to HBr. However, HBrO3 is a stronger acid than HIO3 sinceBr is more electronegative than I, causing the inductive effect of HBrO3is stronger, hence the dissociation is stronger.


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I ,

HC :

HC :

I , , ,

16 HCl + 2 KMnO4 2 KCl + 2 MnCl2 + 8 H2O + 5 Cl2

4 HCl + MnO2 MnCl2 + 2 H2O + Cl2

.

I


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I , , , ()

H :

H :

.

2 Cl 2 e + Cl2

Na+ + e Na


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D , .

, ..

brine

Wh di hl id di i t d th ff t f l t i


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When sodium chloride dissociates under the effect of an electriccurrent, the chloride ions are discharged.

At anode : 2 Cl-

(aq)

Cl2 (g) + 2e-

. Titanium is chosen as the anode because it resists corrosion by the

very reactive chlorine

At cathode, since the sodium ion (Na+) is attracted to cathode

through the diaphragm, the selectivity to discharge is betweensodium ion and water molecule.

Standard reduction potential of sodium :

Na+ + e- Na E0 = 2.71 V

Standard reduction potential of water :2 H2O (l) + 2 e

- H2 (g) + 2 OH- (aq) E0 =

Since has a higher SRP value, is discharge and... is produced.

The level of brine (left or anode position) is always placed higherthan the water (right or cathode position) to prevent a back pressureof the cell and form back flow. If back flow occurs, water will dilutethe concentrated brine and chlorine will not be selected.

0.83 Vwater water

hydrogen and hydroxide ion


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5.6 Reaction with silver nitrate

When aqueous halide ions (such as,sodium chloride solution) are added to

silver nitrate solution,coloured precipitates are formed.NaCl (aq) + AgNO3 (aq) AgCl (s) + NaNO3

Ag+ (aq) + Cl- (aq) AgCl (s) (white precipitate)

Silver chloride is a white precipitate which dissolves in excess aqueous

ammonia to form a soluble complex of silver

AgCl (s) + 2 NH3 (aq) [Ag(NH3)2]+Cl- (aq) (soluble complex)

,

colour (AgBr)Ag+ (aq) + Br- (aq) AgBr (s) (cream precipitate)

Unlike silver chloride, silver bromide dissolve only in concentrated

ammonia aqueous solution according to the equation :

AgBr (s) + 2 NH3 (aq) [Ag(NH3)2]+Br- (aq) (soluble complex)

If iodide ion is replaced, silver iodide (AgI) produced is yellow colour

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


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5.7 Reaction with aqueous sodium hydroxide

Chlorine reacts with dilute sodium hydroxide solution to form sodiumhypochlorite and NaCl.(low temp)

Cl2 (g) + 2 NaOH (aq) NaCl (aq) + NaClO (aq) + H2O (l)

* When NaClO is exposed to uv (sunlight) it will undergoes

decomposition to form sodium chloride and oxygen gas.

2 NaClO a 2 NaCl a + O

0 1 +1

The reaction above can also be describe as a futher decompositionupon heating hypochlorite ion

3 NaClO (aq) NaClO3 (aq) + 2 NaCl (aq)

When concentrated sodium hydroxide is heated to a high

temperature of 70oC, sodium chlorate(v) is formed.

3 Cl2 (g) + 6 NaOH (conc) 5NaCl (aq) + NaClO3 (aq) + 3 H2O (l)

+1 1+5

0 1 +5


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For bromine, it behave the same way as chlorine. When bromineis added to aqueous sodium hydroxide

3 Br2 (l) + 6 NaOH (aq) NaBrO3 (aq) + 5 NaBr + 3 H2O

Iodine reacts with NaOH in the same ways Cl2 and Br2.

Disproportionation occurs even at 0oC.

01+5

2

+ a aq a3

aq + a +2

It is therefore impossible to prepare the IO- ions without the

presence of IO3-

0 1+5

5 8 U f H l d Th i C d


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5.8 Uses of Halogen and Their Compounds

Fluorine

As oxidising agents.

Hydrogen fluoride is used to etch glass.

Sodium fluoride is added to the water and toothpaste to prevent

dental caries.

Fluorine in industry is the production of polymer plastic-teflon.Teflon

is an insulator of electricity and as linings in non- stick pans

.Medically,teflon is an important material in surgical transplants as itcan be used to replace broken cartilages.

NaF or SnF2 are important constituents in toothpaste and fluoride

ion,F-, forms a protective layer


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Chlorine

Used as bleaching agents. Bleach contains sodium hypochlorite or

sodium chlorate(I) and prepared by passing chlorine gas into a cold

sodium hydroxide solution.

Cl2(g) + 2NaOH(aq) NaCl (aq) + NaClO (aq) + H2O (l)

Add to water and swimming pool to kill germs and bacteria. In water

forms hydrochloric and hypochlorus acids and ClO- has the

disinfecting effect.

Cl2(g) + H2O (l) HCl (aq) + HClO (aq) Dichlorodiphenyltrichloroethane (DDT) is used as insecticide.

Chloroethene is the monomer for PVC.

Chlorine dioxide,ClO2 is used to bleach wood pulp for papermaking.

Potassium chlorate(V) is used as an oxidant in fireworks and

matches


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B

B .1,2,BCH=CHB .

1,2,BCH2CH2B .

. . ,

,

This is a redox reaction

Ag+ + e- Ag [reduction]

2Br- Br2 + 2 e- [oxidation]Overall Reaction

2AgBr 2 Ag + Br2


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II

.

.

, AI

Chemistry Form 6 Sem 2 06

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Transcript of Chemistry Form 6 Sem 2 06