hydrocarbons

Question 1

organic compounds def

Answer 1

compounds that contain carbon atoms covalently bonded to atoms of other elements, usually hydrogen, oxygen, nitrogen or chlorine.

Question 2

homologous series def

Answer 2

consists of a family of compounds with the same general formula, and similar chemical properties because they have the same functional group

–> gradual change of physical properties as a result of increase in size and mass of molecules

Question 3

functional group def (for understanding)

Answer 3

atom or combination of atoms which gives organic molecules distinctive chemical properties

Question 4

alkanes and functional group

Answer 4

carbon-carbon single bond (C–C)
general formula: CnH2n+2

Question 5

alkenes and functional group

Answer 5

carbon-carbon double bond (C=C)
general formula: CnH2n

Question 6

alcohol and functional group

Answer 6

hydroxyl (—O–H)
general formula: CnH(2n+1)OH

Question 7

carboxylic acid and functional group

Answer 7

carboxyl O
||
—C–O–H
(–COOH)
general formula: C(n-1)H(2n-1) COOH

Question 8

meth- prefix, carbon atoms = ?

Answer 8

1

Question 9

eth- prefix, carbon atoms = ?

Answer 9

2

Question 10

prop- prefix, carbon atoms = ?

Answer 10

3

Question 11

but- prefix, carbon atoms = ?

Answer 11

4

Question 12

–ane suffix, homologous series = ?

Answer 12

alkane

Question 13

–ene suffix, homologous series = ?

Answer 13

alkene

Question 14

–ol suffix, homologous series = ?

Answer 14

alcohol

Question 15

–oic acid, homologous series = ?

Answer 15

carboxylic acid

Question 16

alkanes def

Answer 16

hydrocarbons that contain only carbon-carbon single bonds and carbon-hydrogen bonds

obtained from fractional distillation of petroleum

Question 17

saturated meaning in terms of alkanes

Answer 17

molecule contains only carbon-carbon single bonds. each carbon atom is covalently bonded to four other atoms (single bonds) so no new atom can add to it anymore

Question 18

alkane solubility

Answer 18

insoluble in water but soluble in organic solvents like tetrachlormethane (CCl4)

can be used as solvents for other organic compounds (liquid hexane to alkenes)

Question 19

changes in physical properties as size and mass of alkane molecules increases down series

Answer 19

1. melting point and boiling point increases
2. density increases
3. viscosity increases
4. flammability decreases

Question 20

what happens to alkanes during COMPLETE combustion + equation

Answer 20

alkanes burn with blue flame without smoke

alkane + oxygen gas –> CO2 + H2O

Question 21

what happens to alkanes during INCOMPLETE combustion

Answer 21

alkanes burn with yellow smoky flame to produce products like soot (carbon), CO, H2O

alkane + oxygen –> C(s) + CO (g) + H2O [not always all three]

Question 22

catalyst for a substitution reaction

Answer 22

UV light

Question 23

what happens during a substitution reaction

Answer 23

a hydrogen atom is substituted to form chloromethane and hydrogen chloride is produced too

eg. methane (CH4 (g)) + chlorine (Cl2 (g)) -UV light-> chloromethane (CH3Cl (g)) + HCl (g)

more hydrogen atoms can be replaced to form products like dichloromethane

Question 24

alkenes def

Answer 24

hydrocarbons that contain carbon-carbon double (C=C) bonds

obtained from the cracking of alkanes

Question 25

types of hydrocarbons of alkenes

Answer 25

unsaturated hydrocarbons; contains carbon-carbon double bonds, where each carbon atom is covalently bonded to three atoms only ratio of C:H atoms: 1:2

Question 26

solubility of alkenes

Answer 26

insoluble in water but soluble in organic solvents like hexane and tetrachloromethane not used as solvents as they are reactive, so they can interfere with reactions

Question 27

change of physical properties as size and mass of alkenes increases

Answer 27

1. boiling point increases 2. density increases 3. viscosity increases 4. flammability decreases

Question 28

what happens during combustion of alkenes + eqn

Answer 28

burn with sootier flames than alkanes because the percentage of carbon by mass in alkenes is higher than that in alkanes for the same number of carbon atoms present in respective molecules alkene + oxygen gas --> CO2 + H2O

Question 29

what happens during hydration of alkenes + eqn

Answer 29

1. pressure = 60 atm 2. temperature = 300 degree celsius 3. concentrated phosphoric (V) acid as a catalyst alkenes are converted to alcohol after addition of steam alkene + steam --> alcohol

Question 30

what happens during hydrogenation

Answer 30

hydrogen is added to carbon-carbon double bond at high temperature and pressure to change to alkanes - nickel (transition metal) as catalyst alkene + hydrogen --> alkane

Question 31

what happens during bromination

Answer 31

important test to distinguish alkanes from alkenes 1. alkene: bromine is decolourised 2. alkane: bromine remains brown, no reaction takes place

Question 32

what is polymerisation

Answer 32

it is a process of joining small identical units to form large molecules with a high temperature and pressure and a catalyst

Question 33

what is cracking

Answer 33

it is the breaking down of large alkane molecules to produce smaller useful molecules, with the use of high temperatures and pressures without a catalyst with a catalyst, it is catalytic cracking, which requires aluminium oxide or silicon dioxide as a catalyst, and a high temperature of about 500-700 degree celsius, and a pressure of 1 atm. two different pathways which lead to different product formation 1. large alkane --> mixture of alkenes + alkane 2. large alkane --> mixture of alkenes + hydrogen

Question 34

isomer def

Answer 34

compounds that have the same molecular formulae but different structural formulae

Question 35

straight chain vs branched chain of alkanes

Answer 35

straight: all carbon atoms connecting in a single continuous line branched: carbon atom(s) not connecting in a single continuous line and form a side chain known as alkyl group

Question 36

alkyl group and their names

Answer 36

1. –CH3: methyl 2. –C2H5: ethyl 3. –C3H7: propyl

Question 37

steps to naming isomers

Answer 37

1. look for the longest chain of carbon atoms (main chain), named according to number of carbon atoms 2. identify alkyl groups 3. indicate position of alkyl groups on the main chain. the position must be the lowest possible number