Alkanes

Question 1

Primary hydrogen

Answer 1

H atom bonded to a C atom that is bonded to 1 other C atom

Question 2

Secondary hydrogen

Answer 2

H atom bonded to a C atom that is bonded to 2 other C atoms

Question 3

Tertiary hydrogen

Answer 3

H atom bonded to a C atom that is bonded to 3 other C atoms

Question 4

Why are alkanes non polar

Answer 4

Little difference in electronegativity between C and H, so C-H bonds are non polar

Question 5

Why are alkanes generally unreactive

Answer 5

1. Non polar; no electron rich sites to attract electrophiles and no electron deficient sites to attract nucleophiles
   2; contains strong c-c and c-h bonds that require large amounts of energy to break

Question 6

How is noiling and melting point affected in alkanes

Answer 6

Number of carbon atoms in alkanes imcrease, number of electrons imcrease, size of electron cloud ijcreases, easier to polarise electron cloud, strength of id-id increases, more energy needed to overcome

Question 7

How does degree of branching affect melting and boiling point of alkane

Answer 7

The more branched the isomee of the alkane, molecule becomes more compact, more surface area available for intermolecular interactions, weaker id-id, less energy needed to overcome

Question 8

Solubility of alkanes

Answer 8

Soluble in non polar solvents
Insoluble in water/highly polarnsolvents

Question 9

How does size of alkane affect density

Answer 9

Density of alkanes increases with increasing molecular size of alkanes

Question 10

Reduction of alkanes (page 7)

Answer 10

Alkene reacts with hydrogen under heat and with nickel catalyst to form alkane

Alkene reacts with hydrogen with Pt or Pd catalyst to form alkane

Question 11

Combustion of alkanes

Answer 11

CnH2n+2 + (3n+1)O2 = nCO2 + (n+1)H2O
Complete combustion: CO2 and H2O produced
Incomplete combustion: CO, C as soot formed in additioj to CO2 and H2O

Question 12

Describe halogenation

Answer 12

Reagent; Cl2 or Br2
Condiiton; uv light/heat
Mechanism; free radical subsitution

Question 13

Halogenation with limited Br2

Answer 13

C2H6 (limting Br2, heat) = C2H5Br + HBr

Question 14

Halogenation with excess Br2

Answer 14

C2H6 (excess Br2, heat) = C2Br6 + HBr

Question 15

Characteristics of tree radical

Answer 15

1. is highly reactive because it has a electron deficient site
2. Is electrically neutralas it has equal number of protons and elections

Question 16

How are radicals made stable

Answer 16

The more alkyl groups attached to carbon radical, the more stable the alkyl radical as alkyl groups are electron donatinf and make the radical less electron deficient

Question 17

Define homolytic fission

Answer 17

Bond breaks in such way that each of the atok involved in forming the bond acquires 1 of the 2 bonding electrons to form 2 free radicals

Question 18

Why is light only shone at the beginning of the subsitution reaction

Answer 18

Provides enough energy for some halogen moleculesto undergo homolyticbond fission to form radicals during initiation step
Chain reaction can step and propagation steps can proceed successively for manycycles unaided

Question 19

What is a trace quantity

Answer 19

Compound that wasn’t formed in a propagation step
Contains at least twice the number of C atoms compared to starting alkane
Not the major product

Question 20

How does stability of radical intermediate affect ratio of products formed

Answer 20

More stable radical intermediate and its subsequent is likely to beformed

Question 21

How does type of hydrogenatoms affect ratio of products formed

Answer 21

Subsitution favours hydrogem attached to carbons that lead to more stable radicals