chap 19 hydrocarbons

Question 1

what are hydrocarbons

Answer 1

organic compounds that contain only carbon and hydrogen

Question 2

organic compounds in the same homologous series have? (4)

Answer 2

-same functional group
- same genetic formula
- similar chemical properties
- show a gradual change in physical properties

Question 3

what is the general formula of alkane

Answer 3

CnH2n+2 (n is the number of carbon)

Question 4

what is the structure of alkanes (2)

Answer 4

simple covalent molecules, weak intermolecular forces of attraction

Question 5

physical properties of alkanes (3)

Answer 5

low melting boiling point, insoluble in water but soluble in most organic compounds, alkanes with larger molecules are more viscous (flow less easily)

Question 6

chemical properties of alkanes

Answer 6

generally unreactive due to strong C-C single bonds

Question 7

what happens in the combustion of alkanes

Answer 7

alkanes burn in excess oxygen to produce carbon dioxide and water

Question 8

what happens in a substitution reaction of alkane

Answer 8

alkanes react with halogen in the presence of ultraviolet light, hydrogen atom is replaced

Question 9

general formula of alkenes

Answer 9

CnH2n (n is the number of carbon)

Question 10

what is the functional group of alkenes

Answer 10

C=C

Question 11

is alkane saturated or unsaturated

Answer 11

saturated

Question 12

is alkene saturated or unsaturated

Answer 12

unsaturated

Question 13

what are the three addition reactions for alkenes

Answer 13

addition of bromine (bromination), addition of hydrogen (hydrogenation), addition of steam (hydration)

Question 14

what happens in addition of bromine to the C=C of alkene

Answer 14

C=C bond becomes C-C bond, product name starts with “dibromo” (eg dibromoethane)

Question 15

how to use bromination to test for unsaturated organic compounds

Answer 15

gaseous hydrocarbon is bubbled through aqueous bromine

Question 16

results when alkane is bubbles through aq bromine

Answer 16

brown aw bromine remains brown

Question 17

results when alkene is bubbled through aq bromine

Answer 17

brown aq bromine turns colourless rapidly

Question 18

what happens in hydrogenation

Answer 18

a molecule of hydrogen is added to C=C of alkenes, unsaturated alkenes are converted to saturated alkenes

Question 19

what are the conditions for addition of hydrogen to alkenes

Answer 19

high temperature and nickel catalyst

Question 20

what happens in addition of steam to alkene

Answer 20

a molecule of water is added to the C=C of alkenes, alkenes are converted to alcohols

Question 21

what are the conditions for addition of steam to alkenes

Answer 21

high temperature, 60 atm, phosphoric (V) acid catalyst

Question 22

what is catalytic cracking

Answer 22

is the process by which long chain hydrocarbons are broken down into smaller molecules

Question 23

conditions for cracking to occur (2)

Answer 23

high temperature, catalyst (aluminium oxide and silicon dioxide)

Question 24

what are the uses of cracking (2)

Answer 24

• to convert less useful long chain alkanes into short chain alkanes or alkenes which are in higher demands
• to produce hydrogen as fuel or haber process

Question 25

what are isomers (3)

Answer 25

- compounds with same molecular formula but different structural formula - different chemical compounds as they have different structures and therefore different physical properties like melting boiling points - they have similar chemical properties