module 4

Question 1

properties of alkanes

Answer 1

-general formula - CnH2n+2
-non-polar as theres no significant difference between the electronegativities of carbon and hydrogen
-used as fuels

Question 2

structure and bonding of alkanes

Answer 2

-there are 4 bonding pairs and 0 lone pairs around the C atom
-tetrahedral shape and 109.5
-all electron pairs repel

Question 3

sigma bonds

Answer 3

-caused by end on end overlap of bonding orbitals directly between atoms
-how well they overlap determines bond strength

Question 4

alkanes boiling and melting points - chain length

Answer 4

-as the chain length increases
-the boiling and melting points increase
-longer chains have more points of surface contact between molecules
-increases the strength of induced dipole dipole interactions between molecules
-more energy need to overcome

Question 5

alkanes boiling and melting points - isomers

Answer 5

-the more branches in an isomer molecules the lower the boiling point
-there are less points of surface contact between molecules
-so weaker induced dipole dipole interactions between molecules
-less energy needed to overcome

Question 6

complete combustion

Answer 6

burning of a substance in excess supply of oxygen

Question 7

incomplete combustion

Answer 7

-burning of a substance in a limited supply of oxygen

Question 8

radical

Answer 8

highly reactive species with an unpaired electron

Question 9

homolytic fission

Answer 9

covalent bond breaks and one electron goes to each atom forming two radicals

Question 10

heterolytic fission

Answer 10

covalent bond breaks and both electrons goes to one atom forming two ions

Question 11

pi bonds

Answer 11

sideways overlap of p orbitals to give a pi bond above and below

Question 12

nucleophiles

Answer 12

electron par donator
-regions of high electron density

Question 13

testing for alcohols

Answer 13

-tertiary alcohols don’t react with acidified potassium dichromate
-add a few drops of potassium dichromate and conc. sulphuric acid
-colour change from orange to green shows the presence of 1 and 2 alcohols

Question 14

testing for alkenes

Answer 14

-add bromine water and shake
-colour change from orange to colourless shows the presence of a double bond

Question 15

properties of alcohols

Answer 15

-polar molecules
-due to the elctronegativite hydroxyl groups which pulls the electrons in the C-OH bond away from the carbon atom

Question 16

boiling points of alcohols

Answer 16

-alcohols have higher boiling points than alkanes
-alcohols are less volatile than alkanes of similar carbon atoms

Question 17

solubility of alcohol - short chain lengths

Answer 17

-soluble in water
-alcohol and water molecules make hydrogen bonds with each other
-alcohols make neutral solutions
-the more OH groups the more hydrogen bonds so the alcohol is more soluble

Question 18

solubility of alcohol - long chain lengths

Answer 18

-the greater the chain length the less soluble the alcohol is in water
-there are stronger induced dipole dipole interactions
-which break up hydrogen bonds between molecules

Question 19

properties of alkanes

Answer 19

-formula CnH2n
-unsaturated hydrocarbon with at least one C=C bond
-alkenes are more reactive than alkanes in addition reactions

Question 20

shape and rotation - alkenes

Answer 20

-triganol planar around each atom in the C=C bond
-no rotation around the C=C bond as p orbitals must stay in their position to overlap and form pi bond
-C-C bonds still rotate

Question 21

define stereoisomers

Answer 21

-the same structural formula but different arrangement of atoms in space

Question 22

disposing of waste - polymers

Answer 22

-polymers are unreactive so arent biodegradable
-pro: long lasting and reusable
-con: difficult to dispose of

Question 23

uses of mass spectrometry

Answer 23

-determine the abundance of isotopes in an element
-monitor breathing of patients under anastethic
-testing for drug use
-analysing molecules in space
-testing for toxic chemicals in marine life

Question 24

describe purification through a seperating funnel

Answer 24

-products of a reaction and water is added to the separating funnel, shaken then allowed to settle
-the less dense organic layer settles at the top
-water soluble impurities dissolve in the lower aqueous layer
-open tap using stopper so aqueous layer is run off