2 Alkanes

members different in molar mass is 14 g mol -1 4. Structural Structural formulae formulae of alkane alkaness Name Methane

No. of   isomers 0

Structural formulae and Name H │ H ─ C ─ C ─ H │ H

CH4

Ethane, C2H6

0

Propane, C3H8

0

Butane, C4H10

2

H H │ │ H ─ C ─ C ─ C ─ C ─ H │ │ H H H H H │ │ │ H ─ C ─ C ─ C ─ C ─ H │ │ │ H H H H H H H │ │ │ │ H ─ C ─ C ─ C ─ C ─ C ─ H │ │ │ │ H H H H n-butane

2

H H H │ │ │ H ─ C ─ C ─── C ─── C ─ H │ │ │ H H─ C  ─H H │ H 2 - meth methyl yl propane Pentane, C5H12

3 H H H H H │ │ │ │ │ H ─ C ─ C ─ C ─ C ─ C ─  C ─ C C─H │ │ │ │ │ H H H H H n-pentane H H H H │ │ │ │ H ─ C ─ C ─── C ─── C ─ C ─ C ─ H 1 2 │ │ │3 │ 4 H H─ C  ─H H H │ H 2-met 2-methyl hyl butane  butane

3

H │ H H ─ C ─ C ─ H H │ │ │ H ─ C ─ C ─── C ─── C ─ H │ │ │ H H─ C  ─H H │ H 2,2-dimethyl propane Hexane, C6H14

5 H H H H H H │ │ │ │ │ │ H ─ C ─ C ─ C ─ C ─ C ─  C ─ C C ─ C ─ H │ │ │ │ │ │ H H H H H H n-hexane H H H H H │ │ │ │ │ H ─ C ─ C ─── C ─── C ─ C ─ C ─ C ─ C ─ H │ │ │ │ │ H H─ C  ─H H H H │ H 2 - methyl pentane

4

H H H H H │ │ │ │ │ H ─ C ─ C ─ C ─── C ─── C  ─── C ─ C ─ C ─ H │ │ │ │ │ H H H─ C  ─H H H │ H 3 - methyl pentane H │ H H ─ C ─ C ─ H H H │ │ │ │ H ─ C ─ C ─── C ─── C ─ C ─ C ─ H │ │ │ │ H H─ C  ─H H H │ H 2,2 - dimethyl butane H │ H H H ─ C  ─H H │ │ │ │ H ─ C ─ C ─── C ─── C ─── C ─── C ─ H │ │ │ │ H H─ C  ─H H H │ H 2,3 - dimethyl butane 5

Physical Properties

Physical properties of alkanes i. cannot conduct electrity ii. less dense than water  iii. dissolve in organic solvents, insoluble in water  iv. iv. low low mel meltiting ng an andd bo boililin ingg po poin ints ts Conclusion: - molecule held together by weak intermolecular forces - properties of covalent compound - gradually steady increase as the number of carbon in alkane increases

6

6. Steps to name branched alkanes; i. determined and named the long chains ii. determined and named the branch chain    CH3 : methyl    C2H5 OR   CH2CH3 : ethyl    C3H7 OR   CH2CH2CH3 : prophyl iii. give number to the carbon atoms atoms in long chain, chain, which started from the nearest branched iv. The number for carbon atom which branched emerged from, must put before/infront the alkyl v. Name Namedd the the bran branch ched ed first first,, fol follo lowe wedd by the the nam named ed of long long ch chai ains ns The word “ di, tri” tri” is used if the branched chains is more than one

Chemical Properties Pg 38 Reactivity of alkanes 1. Not reactive/ reactive/unrea unreactive ctive becaus becausee saturated hydrocarbon 2. Did not decolou decolourized rized purple purple solution solution of acidified potassium manganate(VII)

3. Did not decolourized reddish brown solution solution of  of  bromin water 4. Neut Neutra ral.l. Combustion of alkanes 1. In the the presence of sufficient oxygen, alkanes burns to form carbon dioxide and water. – complete combustion Chemical equation: i.

CH4

+

O2



CH4 + 2O2



CO2

+

H2O

CO2 + 2H2O 7

ii.

C2H6

iii.

C4H10 + 13/2 O2



C6H14



iv.

+ 7/2

O2



+ 19/2 O2

2CO2

+ 3H2O

4CO2

+ 5H2O

6CO2

+

7H2O

Answers

i. CH4

+ 2O2

ii. C2H6

+

2 x C 2H 6

+ 2 x 7 O2 2

2C2H6

7 O2 2

+

CO2

→

2CO2 +



7 O2

iii.

C4H10 + 13/2 O2

iv.

C6H14 + 19/2 O2

+ 2H2O



3H2O

2x 2CO2 + 2x 3H2O



 

4CO2 +

6H2O

4CO2 + 5H2O 6CO2 + 7H2O

C3H8 C5H12 8

C7H16 C8H18 C9H20 C10H22 2. If there is insufficient oxygen, oxygen, carbon monoxide or carbon may be formed – incomplete combustion i.

CH4 + 3/2 O2  CO + 2H2O 2CH4 + 3 O2  2CO + 4H2O ii. CH4 + O2  C + 2H2O

Halogenation

The reaction is between alkane dan chlorine. Takes place under sunlight/ultra violet light. Carbon-hydrogen bonds broken and new carbon-halogen bonds are formed. formed. One or more hydrogen atoms in alkanes molecule may be subtituted by halogen. 4. Halogenation is substitution reaction.

1. 2. 3.

One atom or a group of atoms in a molecule is replaced by another atom or group of  atoms.

Chlorination of methane First stage; H │ H ─ C ─ C ─ H ─ H +Cl-Cl +Cl-Cl → │ H

H | H — C — C —  — Cl Cl + HCl | H monochloromethane

9

Second stage; H │ H ─ C ─ C ─ Cl + │ H

→

Cl | H — C — C  — Cl + HCl | H dichloromethane

Cl2

→

Cl | H — C — C  — Cl + HCl | Cl trichloromethane

Cl2

Cl | → Cl —  — C C  — Cl + HCl | Cl tetrachloromethane tetrachloromethane

Cl2

Third stage ; Cl │ H ─ C ─ C ─ Cl + │ H

Fourth stage; Cl │ H ─ C ─ C ─ Cl + │ Cl

Overall equation/chemical equation CH4 + 4Cl2 CCl4 + 4HCl

HW: PG41 EP B no. 1-3 Prepared; Kamal Ariffin Bin Saaim SMKDBL

10

Alumina, Al2O3 C9H20 (ce) ———— → Panas Nonana

Alumina, Al2O3 C9H20 (ce) ———— → Panas Nonana

C2H6 (g)

+

C7H14 (g)

Etana

C2H6 (g)

Heptena

+

Etana

C7H14 (g)

Heptena

11