Redox, halogens, group 1 and 2 and 7 titrations Flashcards
0
Q
What is the loss of electrons?
A
Oxidation.
1
Q
What is the gain of electrons?
A
Reduction.
2
Q
What is more electronegative? Carbon or oxygen?
A
Oxygen.
3
Q
What is the oxidation number of a molecule?
A
0
4
Q
What is the oxidation number of an un combined element?
A
0
5
Q
In a simple ion, what is the oxidation number?
A
The charge of the ion e.g. In calcium chloride the metal is Ca²⁺ ion and the oxidation number of calcium is 2+
6
Q
What is the oxidation number of hydrogen?
A
+1 (except in metal hydrides where it is -1)
7
Q
What is the oxidation number of fluorine?
A
-1
8
Q
What is the oxidation number of oxygen?
A
-2
except in peroxides,(-1) O₂²⁻ and compounds with fluorine.
9
Q
What is the oxidation number of chlorine, bromine and iodine?
A
-1 except in compounds with oxygen and fluorine.
10
Q
When 2 atoms are in a covalent bond, which will have what oxidation number?
A
The more electronegative one will have a negative oxidation number.
11
Q
What is reduction?
A
The gain of hydrogen or the loss of oxygen.
12
Q
What are oxidation numbers?
A
Systems of electron counting.
13
Q
What is the symbol of an oxidising agent?
A
[o]
14
Q
What is the symbol of a reduction agent?
A
[H]
15
Q
What are oxidation states?
A
The same as oxidation numbers
16
Q
What do oxidising agents do?
A
Gain electrons and get reduced.
17
Q
What do reducing agents do?
A
Donates electrons and gets oxidised.
18
Q
What is the oxidation number of a simple monatomic ion?
A
The same as the charge. An example is Na⁺
19
Q
In copper (II) sulfate, what is the oxidation number of copper?
A
+2
20
Q
When an electron is lost, what happens to the oxidation number?
A
Increases by 1
21
Q
What an electron is gained, what will happen to the oxidation number?
A
It will decrease by 1
22
Q
What is disproportionation?
A
When an element is oxidised and reduced at the same time.
23
Q
What is the trend with group 2 metals and ionisation energy?
A
It decreases down the group as:
Each element down has an extra electron shell.
The inner electron shells shield the outer ones.
The outer electrons are further away.
Thus the outer electrons is easier to remove.
24
How do group 2 elements react with water?
They give a metal hydroxide and hydrogen. They get increasing more reactive down the group as ionisation energy decreases.
These metal hydroxides dissolve to give OH⁻ ions.
25
How do group 2 metals react with oxygen when burnt?
They form solid white oxides.
| They burn with characteristic flame colours. These oxides act as bases and produce metal hydroxides when added to water.
26
How do group 2 metals react with chlorine?
They form white sold chlorides.
27
Does beryllium react with water?
No
28
Does magnesium oxide react with water?
Yes but very slowly. The oxide it gives isn't very soluble meaning it doesn't form a very alkali solution.
29
What happens when a group 2 metal oxides react with acid?
It will produce water and a something elss.
30
When group 2 metals form singly charged negative ions like MgOH⁻ what is the trend in solubility?
It increases down the group.
31
When group 2 metals form double negative ions like with SO₄²⁻ what is the trend with solubility ?
It decreases down the group.
32
Is barium sulphate soluble ?
No, unlike most sulphates.
33
For group 1 and 2 carbonates and nitrates what is the trend with thermal stability? Why is this?
It increases down the group.
Carbonate and nitrate ions are large and can be made unstable by the presence of cations. It polarises the anion, distorting the electron field and making it unstable.
Larger cations cause less distortion so are more stable.
34
Are group 2 compounds less or more thermally stable than group 1 compounds?
Why?
Less stable.
The greater the charge on the cation, the greater the distortion and the less stable it is. Group 2 metals have a 2+ charge as opposed by 1+ charges of group 1 metals.
35
Can you thermally decompose group 1 carbonates with a bunson burner?
No as they are too stable and so need high temps to decompose.
(Apart from Li₂CO₃ with will form Li₂O and CO₂)
36
How do group 2 carbonates thermally decompose?
They form CO₂ and the oxide.
37
Explain the thermal decomposition of of group 1 nitrates
They decompose to form oxygen gas and a nitride. (XNO₂)
| except LiNO₃ which decomposes to form Li₂O, NO₂ and O₂ which is the same way as group 2 nitrates.
38
How do group 2 nitrates thermally decompose
They give the oxide, nitrogen dioxide and oxygen.
39
How would you test the thermal stability of a nitrate?
Time how long it takes for it to produce oxygen gas or brown fumes of NO₂
40
How would you test the thermal stability of a carbonate?
See how long it takes to produce CO₂
41
When doing a flame test, what colour does Li give?
Red
42
When doing a flame test, what colour does Na give?
Orange/yellow
43
When doing a flame test, what colour does K give?
Lilac
44
When doing a flame test, what colour does Rb give?
Red
45
When doing a flame test, what colour does Cs give?
Blue
46
When doing a flame test, what colour does Ca give?
Yellow red
47
When doing a flame test, what colour does Sr give?
Crimson.
48
When doing a flame test, what colour does Ba give?
Green
49
How do you do a flame test?
Mix a small amount of compound with HCl.
Heat a piece of platinum or nichrome wire in a Bunsen to clean it.
Dip the wire in the mixture and put in the hottest part of the flame.
50
Why do different compounds give different colours?
The electrons in the atoms absorb energy and then release it in the form of photons as they drop energy levels. These are of different wavelengths meaning different colours.
51
What is the trend with electronegativity in the halogens?
It increases up the group.
52
What does fluorine look like?
A pale yellow gas.
53
What does chlorine look like?
A green gas.
54
What does bromine look like?
A red-brown liquid.
55
What does iodine look like?
Grey solid.
56
Are halogens soluble in water?
No as they are covalent.
57
Colour of chlorine in water.
Virtually colourless.
58
Colour of bromine in water?
Yellow/orange
59
Colour of iodine in water?
Brown.
60
What is the trend with reactivity with halogens?
They get less reactive down the group.
They react by gaining electrons. They are reduced and act as oxidising agents.
As you go further down, they get bigger meaning more electron shielding meaning the electrons that need to be gained feel less of an attractive force. They become less oxidising.
61
What is the trend with melting and boiling points with halogens?
They increase down the group.
62
What happens when halogens react with alkalis?
They get disproportionated.
63
When a halogen reacted with an alkali, what difference does it make when the alkali is hot or cold?
If it is cold, it will produce water, NaXO and NaX (Na has been used as an example here)
If hot, water, NaX and NaXO₃
64
What is the trend with the reactivity of halides?
They can act as a reducing agent by losing an outer shell electron.
As you go down the group, the bigger the ion and so the bigger the distance and the greater the shielding. Thus is is easier to remove the outer shell electrons.
The reducing power of halides increases down the group.
65
How do the halides react with sulphuric acid?
Before hand they may have bonded to potassium.
KF + H₂SO₄ → KHSO₄ +HF. They always give a hydrogen halide which will be shown as misty fumes.
Any HCL or HF that could be produced isn't a strong enough oxidising agents to reduce the acid so the reaction stops.
Is isn't a redox reaction.
66
How does KBr react with H₂SO₄
KBr + H₂SO₄ → KHSO₄ + HBr.
The HBr acts as a reducing agent to the acid.
2HBr + H₂SO₄ → Br₂ + SO₂ + 2H₂O.
67
How does KI react with H₂SO₄?
KI + H₂SO₄ ➲ KHSO₄ + HI
2HI + H₂SO₄ ➩ I₂ + SO₂ + 2H₂O
Then the HI reduced the SO₂ as well.
6HI + SO₂ ➛ H₂S + 3I₂ + 2H₂O
68
What are the properties of hydrogen halides?
Colourless gases.
Very soluble, dissolving in water to form strong acids.
They react with ammonia gas to give white fumes.
NH₃ + HCL ⇒NH₄Cl
69
What can displace a halide ion?
A solution of more reactive halogen.
70
When seeing if a halide ions will be displaced by a solution of a different halogen what makes is easier to see the colour change?
Add an organic solvent like hexane. The halogen will dissolve in it and form a layer under the purple hexane layer.
The colour of the bottom layer will be that of the displaced halogen in water.
71
What halogen will displace what halide?
A halogen will displace a halide from a solution if the halide is below it in the periodic table. It will oxidise it.
72
Before testing the type of halide by adding silver nitrate, why do you add dilute nitric acid before?
To remove ions that might interfere with the test.
73
How do silver halides react with the sun?
Light will cause them to decompose to silver and the halogen.
74
What do you do when doing and acid base titration?
Use a pipettes to measure out some alkali and add some phenolphthalein.
Do a rough titration so you know where the end point is.
When the colour changes is when it has been neutralised.
phenolphthalein will go from red to colourless when adding acid to alkali.
75
What do iodine sodium thiosulfate titrations find?
The concentration of an oxidising agent. The greater the concentration, the more ions that will be oxidised by a set volume of it.
76
If you wanted to find the concentration of a solution of the oxidising agent potassium iodate, what would you do?
Measure out a certain amount of the oxidising agent.
Add this to an excess of acidic potassium iodide solution. This should produce lots of iodine.
Titrate this with sodium thiosulfate. (Know the concentration)
When the solution goes to pale yellow, add starch solution. Then it goes dark blue. Add it drop by drop untill the blue goes away.
77
How does the iodine react with thiosulphate ions?
I₂ + 2S₂O₃²⁻ ⇉ 2I⁻ + S₄O₆²⁻
78
Give the equation of the thermal decomposition of magnesium nitrate.
2Mg(NO₃)₂ ⇢ 2MgO + 4NO₂ + O₂
79
What colour does Mg give in a flame test?
Colurless.
80
What happens when magnesium reacts with cold water, what about hot steam?
As a general rule, if a metal reacts with cold water, you get the metal hydroxide. If it reacts with steam, the metal oxide is formed. This is because the metal hydroxides thermally decompose (split up on heating) to give the oxide and water.
81
What is is the equivalence point?
A specific stoichometoric ratio of reactants and products. This is theoretical. We want to get it but never do.
82
Why is iodine dissolved in KI?
It has limited solubility in water.
| I₂ + I⁻ ⇆ I⁻₃ . The I⁻ comes from the KI and it is the I⁻₃ that we actually titrate.
83
What is a problem with thiosulphate in titrations?
It is unstable in acid conditions.
| 4e⁻ + S₂O₃ ²⁻ +6H⁺ ⇨ 2S + 3H₂O
84
Why is the starch added close to the end?
To avoid the formation of a starch iodine complex meaning it won't work.
85
What can p and d block elements do with their oxidation states?
They can change be a greater amount as the outer shells can be expanded.
86
When a group 2 metal forms a chloride, what affects the electrical conductivity?
The size of the ion.
87
What is the equation for the thermal decomposition of lithium nitrate?
4LiNO"3" = 2Li"2"O + 4NO"2" +O"2".
| This is the same as the decomposition of group 2 nitrates.
