ES Flashcards
(79 cards)
1
Q
Describe the halogens
A
- found in the p-block
- group 7
- occur as diatomic molecule with covalent bonds
- have weak IDIDB between molecules
- down the group:
-become darker in colour
-m.p./b.p. increases
-reactivity decreases
-become less volatile - ## partially soluble in water. more soluble in non-polar solvent
2
Q
explain why reactivity decreases down group 7
A
the most reactive halogens are the strongest oxidising agents
the attraction between the nuclear core an the electron that completes the outer shell weakens due to each atom down the group having another complete shell, increased shielding and atomic radius
- fluorine is the most reactive as it has the IDIDBs
3
Q
What are IDIDBs?
A
instantaneous dipole-induced dipole bonds
4
Q
How can a halogen atom achieve stability?
A
- gain an electron from a metal atom, ionic
- share an electron with a non-metal atom, covalent
5
Q
Why does boiling point increase down group 7?
A
- more electron shells
-stronger instantaneous dipoles - stronger induced dipoles on neighbouring molecule
- stronger IDIDBS
- requires more energy to overcome
6
Q
what colour are halide ions?
A
colourless
7
Q
What happens when halogens react with halide ions?
A
a displacement reaction/ redox reaction if the halogen is more reactive than the halide
8
Q
what happens when halide ions react with silver ions?
A
a silver halide will be precipitated
9
Q
what is added to help distinguish between silver halides?
A
ammonia solution
10
Q
what colour is AgCl and what is its solubility in ammonia?
A
white precipitate
soluble in dilute solutions
11
Q
what colour is AgBr and what is its solubility in ammonia?
A
cream precipitate
soluble in concentrated solutions
12
Q
what colour is AgI and what is its solubility in ammonia?
A
pale yellow precipitate
insoluble
13
Q
halogen + metal=
A
salt
14
Q
halogen + hydrogen =
A
hydrogen halides
- dissolve in water to produce acidic solutions
15
Q
oxidation is:
A
- gain of oxygen
- loss of electrons
- increase in oxidation number
16
Q
reduction is:
A
- loss of oxygen
- gain of electrons
- decrease in oxidation number
17
Q
what is a redox reaction
A
a reaction that involves both oxidation and reduction
18
Q
what can oxidation numbers also be called?
A
oxidation states
19
Q
why are oxidation numbers useul?
A
- in naming inorganic compounds
- recognising oxidation/reduction in a reaction
- recognising the oxidising /reducing agents
- balancing equations
20
Q
What is an oxidation state?
A
indicates how much a molecule/ion is oxidised or reduced
21
Q
What are the rules for oxidation states?
A
- atoms in elements are in oxidation state 0
- in simple ions the oxidation state is the same as the charge on the ion
- in complex ions the sum of all the oxidation states of constituent atoms is equal to the overall charge
22
Q
The _____________ halogen will ___________ the halide ions of the less __________ one
A
more reactive
displace/oxidise
reactive
23
Q
describe reducing agents
A
- usually a metal or negative ion
- loses electrons to another element or ion
- is itself oxidised
24
Q
describe oxidising agents
A
- usually a non-metal or positive ion
- causes oxidation reactions to take place
- gains electrons from other atoms or ions
- is itself reduced
the strongest oxidising agents are highly electronegative elements
25
What can oxidising agents be used for?
- kill fungi and bacteria
- form aldehydes, ketones and carboxylic acids from alcohols
26
How are oxidation states shown in systematic names?
- roman numeral showing oxidation state
applies to preceding element
27
define oxyanions
a negative ion with oxygen in it
- name always ends in -ate
28
What colour is chlorine in aqueous solutions and solutions in cyclohexane?
pale green
pale green
29
What colour is bromine in aqueous solutions and solutions in cyclohexane?
yellow/orange
red/brown
30
What colour is iodine in aqueous solutions and solutions in cyclohexane?
brown
purple/violet
31
What is a disproportionation reaction?
a reaction in which the same element is both oxidised and reduced
32
Define electrolysis
decomposing a compound using an electric current
33
define co-products
additional producs that are made alongside the wanted product
34
for electrolysis ions must.....
be free to move
35
describe cations
- positive
- usually metal
- migrate to cathode
- are reduced
36
describe anions
- negative
- usually non-metals/hydrogen
- migrate to anode
- are oxidised
37
Is the cathode negative or positive?
negative
38
Is the anode negative or positive?
positive
39
What is the problem with electrolysing solutions?
water can also dissociate into H+ and OH- ions so can be a product
- there is competition at the electrode
40
What is reduced at the cathode?
- positive ions
- the least reactive metal/hydrogen
41
what is oxidised at the anode?
- negative ions
- halide ions first then the OH- ions then other negative ions1
42
WHat happens when the electrodes are made of the same metal that is being electrolysed?
the anode will lose mass and the ions will be deposited at the cathode
- used in electrplating
43
What is the equation for the oxidisation of water?
- at anode
2H2O -> O2 + 4H+ +4e-
44
What is the equation for the reduction of water?
- at cathode
2H2O + 2e- --> 2OH- + H2
45
define dynamice equilibrium
is established in a closed system when:
- the rate of the forward reaction is the same as the rate of the reverse reaction
- the concentratons of the reactants and products remain constant
46
in dynamic equilibrium can the concentrations of products to reactants be different?
yes
47
What does it mean when Kc > 1?
more product than reactants at equilibrium
48
What does it mean when Kc >>1?
- greater than 10*10*
reaction appears to have gone to completion
49
What does it mean when Kc < 1?
more reactants than products at equilibrium
50
What does it mean when Kc << 1?
- less than 10*-10*
reaction appears to have not happened
51
True are false: all reactions are equilibrium reactions
true
52
Kc is _____________ dependent
temperature
-temperature will be quoted alongside the constant
53
What safety measures are taken when transporting chlorine?
- transported as a liquid to move a lager volume at once
- pressure vents to release a build up of gas
- lined with strong steel
- tanks must be dry to prevent the formation of acid
- protective housing on top that all loading and unloading happens through
- large tanks will have a excess flow valve
However it is preferably made of site
54
What safety precautions are taken in the unloading of chlorine?
Any air displaced from the tanks must pass through a scrubber unit. This contains sodium hydroxide solution that will react with and chlorine in the air ti form sodium chlorite/bleach.
55
what test is used to check for a chlorine leak?
A stick with a cloth soaked in ammonia. White cloud will be produced in presence of chlorine.
56
List the uses of chlorine
- water treatment
- household bleach and cleaning products
- remove stains from fabric
57
Are iodine-thiosulfate titrations redox?
Yes
58
What colour will iodine be?
Brown
59
What colour will iodine turn t=in the presence of thiosulfate solution?
Brown to place yellow and eventually colourless
60
what can used to make the end point in an iodine-thiosulfate titration easier to see?
Starch solution
Add when iodine is pale yellow
Will be blue/black and turn colourless
61
addition reactions have ________ atom economy. Why?
100% as they only form one product
62
what halogen is the strongest oxidising agent?
Fluorine
63
Sodium fluoride reacts with _________ to make ______.
Concentrated sulfúrico acid to make hydrogen fluoride
64
Sodium chloride reacts with ___________ to make ________ and ________ is seen?
Concentrated sulfúrico acid to make hydrogen chloride gas that will react with water so white fumes are seen
65
Describe the reaction of sodium bromide to form hydrogen bromide
- first reacts with concentrated sulfuric acid to produce hydrogen bromide
- however the bromide ions are strong reducing agents so with reduce the sulfuric acid into sulfur dioxide, SO2
- product will be impure: sulfur dioxide, hydrogen bromide and bromine vapour
66
Describe the reaction of sodium iodide to from hydrogen iodide
- first reacts with concentrated sulfuric acid to make hydrogen iodide
- the iodide ions are strong reducing agents so will reduce sulfuric acid into hydrogen sulfide gas, H2S
- product is impure: sulfuric acid, hydrogen sulfide
67
what other acid can be used to make pure hydrogen bromide/iodide?
Concentrated phosphoric acid
68
Thermal stability __________ down the group. Why?
Decreases because the bond strength hydrogen and the halogen decreases so less energy is needed to break the bond
69
Describe what happens when the hydrogen halides are heated
- both hydrogen fluoride ad chloride don’t break down
- brown bromide gas will be made when HBr is strongly heated
- purple iodine gas is made in presence of red hot needle
70
Acidity _______ down group 7
Increases
All hydrogen halides will dissociate (besides HF) in to acid
- very soluble
71
what is made when hydrogen halides react with ammonia?
An ammonium halide
NH3 + HX -> NH4X
72
what is the test for sulfur dioxide, SO2?
Will turn potassium manganate from purple to colourless
73
What is the test for hydrogen sulfide, H2S?
Will form a black precipitate with lead ethanoate
74
Define Le Chatelier’s principle
When a system in dynamic equilibrium is subjected to change, the position of equilibrium will shift to minimise change
- in a reversible reaction at dynamic equilibrium, the position of equilibrium will shift in order to counteract any changes made
75
What will affect the position of equilibrium?
- concentration
- pressure (in gas phase)
- temperature
76
A catalyst does _______________ the position of equilibrium. It _____________ the _________ at which equilibrium is ___________.
Not change/shift
Increases
Rate
Established
77
What is the Deacon process?
4HCl + O2 <=> 2Cl2 + 2H2O ^H= -144kJmol*-1*
- developed by Henry Deacon in 1874
- used to produce chlorine
78
What are the best conditions for the deacon process to optimise yield of chlorine?
- high pressure
- low temperature
- excess oxygen
79
What is the equation for the formation of bleach?
Cl2 + 2NaOH <=> Na + NaClO + H2O
