CH5 Flashcards
(82 cards)
1
Q
What is a redox reaction?
A
A reaction in which something is oxidised and something else is reduced.
2
Q
Define oxidation
A
Loss of electrons OR oxidation state becoming more positive
3
Q
Define reduction.
A
Gain of electrons OR oxidation state becoming more negative.
4
Q
Define standard electrode potential (Eᶿ)
A
The potential difference when any half-cell is connected to the standard hydrogen electrode under standard conditions
5
Q
Define amphoteric
A
A substance that can react with both acids and bases.
6
Q
Define inert pair
A
ns² Pair of electrons not involved in bonding
7
Q
Define co-ordinate bond
A
Shared pair of electrons, both from the same atom.
8
Q
Define dimer
A
A species created when two molecules join together.
9
Q
Define electron deficient
A
A species with fewer than eight electrons in its outer shell, so this shell is not full.
10
Q
Define lone pair
A
Pair of electrons in an outer shell that are not involved in bonding
11
Q
Define isoelectronic
A
Same number of electrons in the outer shell
12
Q
Define acidic oxide
A
Oxide that reacts with bases.
13
Q
Define basic oxide
A
Oxide that reacts with acids
14
Q
Define disproportionation
A
A reaction where atoms of the same element become oxidised and reduced to form two different products.
15
Q
define transition elements
A
elements with partially filled d-orbitals in their atoms or ions
16
Q
define ligand
A
a small molecule with a lone pair that can bond to a transition metal ion.
17
Q
define complex (in terms of ligands)
A
ligands joined to a transition metal by co-ordinate bonds
18
Q
define monodentate
A
ligand that has one atom that can bond to a metal ion
19
Q
define bidentate
A
ligand that has two atoms that can bond to a metal ion
20
Q
in terms of rate = k[A]ᵐ[B]ⁱ , what is the overall reaction order?
A
m + i
21
Q
define rate determining step
A
the slowest step in a reaction mechanism
22
Q
define an acid
A
H⁺ ion donor (a proton donor)
23
Q
define a base
A
H⁺ ion acceptor (a proton acceptor)
24
Q
what are oxidising agents?
A
they become reduced as they oxidise something else.
25
what are reducing agents?
they become oxidised as they reduce something else.
26
what does the sum of all the oxidation states equal to?
the charge of the species.
for a species with no charge the sum = zero.
27
when the oxidation states becomes more positive is it oxidation or reduction?
oxidation
28
when the oxidation state becomes less positive or more negative, is it oxidation or reduction?
reduction
29
when writing cell diagrams what does ||, | and a comma mean?
|| means the salt bridge
| means a change in state
, goes between species in the same physical state
30
when writing cell diagrams which metal do you put on the left?
the metal with the most negative Eᶿ goes on the left.
31
when creating electrochemical cells what type of voltmeter do we use?
high-resistance voltmeter
32
what do we use to measure the standard electrode potential (Eᶿ)?
the standard hydrogen electrode
33
how do we make a standard hydrogen electrode?
H2 gas
1 atm
inert platinum electrode in 1 mol dm-3 H+ (aq)
298K
34
what is the standard electrode potential of the standard hydrogen electrode?
0 volts
35
how do you find the standard potential of a cell? explain why this formula is used?
standard potential of cell = Eᶿ (more positive) - Eᶿ(less positive)
the more positive the value of the Eᶿ the more likely the system is to gain electrons. if you connect two half-cells together, electrons will flow from the more negative half-cell to the more positive one.
36
how can we tell if the reaction is feasible? (in terms of emf)
EMF = Eᶿ for reduction - Eᶿ for oxidation
the EMF must be positive for the reaction must be positive.
37
What does Eᶿ stand for?
Standard electrode potential
38
what do we use to measure Cu2+ concentration?
thiosulfate
39
what are the advantages of the hydrogen fuel cell?
* water is the only product, so no carbon dioxide (a green house gas) is produced.
* highly efficient, as less energy is wasted as heat, so much more energy is used effectively.
* hydrogen gas can be produced using renewable resources by the electrolysis of water.
* hydrogen can be produced from water, which is a sustainable resource.
40
what are the disadvantages of hydrogen fuel cells?
* hydrogen gas is highly flammable and difficult to store.
| * hydrogen gas is usually produced from fossil fuels, which leads to a net energy loss.
41
in terms of p block elements, what are the two factors that affect whether these elements reach their maximum oxidation values?
octet expansion and the inert pair effect
42
what is octet expansion?
for compounds in groups 5 or 6 to form their highest oxidation states, they would need 5 or 6 covalent bonds giving 10 or 12 electrons in their outer shell.
elements in period 3 downwards have outer electrons in the d orbital. this means they can form more bonds because they can expand their octet by using the d-orbitals.
43
what is the inert pair effect?
going down the p-block the ns2 pair of electrons are less able to be involved in bonding, so we call them an inert pair.
this makes the elements lower in the group show an oxidation state 2 lower than the group number. the stability of the lower oxidation state becomes greater as you go down the group.
44
due to the inert pair effect the elements of group 3 will have a oxidation state of ...
+1
45
describe the compound of aluminium chloride due to its electon deficency.
* chlorine atoms have three lone pairs each.
* this allows co-ordinate bonds to form between a chlorine atom of one AlCl3 and the aluminium atom of another
* with two co-ordinate bonds between AlCl3 monomers forming a dimer.
46
AlCl3 can also co-ordinate bond to a chloride ion to form the tetrachloroaluminate ion, AlCl4-. what two areas of chemistry is this formation used for?
* chloronation of benzene - AlCl3 is called a halogen carrier.
* ionic liquids - liquids at room temp. that contain AlCl4- anions. they are being developed as solvents and catalysts for reactions such as the polymerisation of alkenes.
47
what are the advantages of ionic liquids?
* they make it much easier to separate the products from the reactants and solvent
* their low volatility means the liquid doesn't evaporate during use.
48
what is a donor-acceptor compounds?
when an electron deficient bonds with something that donates a lone pair to the bond that is made. thus one donates and one accepts the lone pair.
e.g. BF3 + NH3 --> NH3.BF3
49
boron nitride is _______ with carbon and so it forms similar structures to the allotropes of carbon: graphite, diamond and nanotubes. fill in the blank.
isoelectronic
50
what are the differences between hexagonal boron nitride and graphite?
* the hexagons in boron nitride have the atoms lying above one another. in graphite they don't.
* boron nitride acts like an insulator while graphite can carry electricity
51
what are the similarities between boron nitride and graphite?
* they both have covalent bonds between atoms.
| * they both can be used as lubricants
52
what shape is cubic boron nitride similar to in terms of carbon.
diamond
53
what are the properties of cubic boron nitride?
```
same tetrahedral arrangement as diamond.
one of the hardest materials known
high melting temperature
excellent heat conductor
chemically unreactive
```
54
what are the uses of cubic boron nitride?
mounting high power electronic components
as wear-resistant coatings
supports for catalysts
55
what is the use for boron nitride nanotubes?
used to wrap around carbon nanotubes to act as an insulating layer to keep the current within the carbon nanotube.
56
in terms of group 4, what type of bonding will there be at the top of the group and at the bottom?
at the top they are non-metals so they will have covalent bonding
at the bottom they are metals so there will be metallic bonding.
57
what two metal ions form a yellow precipitate with iodide ions?
silver and lead(||)
58
When a transition metal forms a complex it causes the d-orbitals to ________?
Split
59
When the d-orbitals split, what energy levels does it form?
2 higher energy orbitals
| 3 lower energy orbitals
60
The colour seen is made up of _______?
The frequencies not absorbed.
61
What causes different ligands to have different colours?
They cause different splitting of the d-orbitals, so different frequencies are absorbed and this gives different colours.
62
What is the colour of chromium(|||), Cr3+, solution?
Green
63
What is the colour of iron(||), Fe2+ , solution?
Pale green
64
What is the colour of iron(|||), Fe3+ , solution?
Yellow
65
What is the colour of copper(||), Cu2+, solution?
Blue
66
What is the observation of chromium(|||), Cr3+, with NaOH (aq)?
Grey-green precipitate
67
What is the observation of iron(||), Fe2+, with NaOH (aq)?
Dark green precipitate
68
What is the observation of iron(|||), Fe3+, with NaOH (aq)?
Red-brown precipitate
69
What is the observation of copper(||), Cu2+, with NaOH (aq)?
Pale blue precipitate
70
____________ turns back to its original green solution when excess NaOH (aq) is added to it.
Chromium(|||), Cr3+
71
What is the colour change for the reduction of iodine?
Brown to colourless
72
How does a transition metal act as a catalyst?
The reactants use vacant d-orbitals to form temporary bonds with the catalyst which holds the reactants so that reaction can take place.
73
When a complexes d-orbital split there is a ΔE between the lower and higher energy orbitals. What determines the value of ΔE?
* the identity of the metal
* its oxidation state
* the nature of the ligands in the octahedral complex
74
What formula matches ΔE and f (frequency)?
ΔE=hf
75
Give one example of the uses of trace elements in living systems.
• Vanadium. This is found in some marine creatures.
• Manganese. Is found in bones, tissues and some organs. It is present in many enzyme systems.
Like many trace elements the daily requirement is vague being about 3 mg per day. Major sources
are nuts and unrefined cereals.
• Iron. Iron is present in the blood in haemoglobin. The iron occupies a similar place in the
porphyrin structure in haemoglobin, to magnesium in the porphyrin structure in chlorophyll. It is present in all tissues and organs and is excreted slowly by the body so that iron is a necessary part of a healthy diet. Large intakes of iron are to be avoided although at such times as pregnancy iron supplements are usually prescribed by doctors. Common forms of iron supplements are in the form of iron(II) sulphate, iron(II) fumarate and iron(II) gluconate. Iron deficiency leads to anaemia.
• Cobalt. This is a component of vitamin B12
• Chromium. This is a cofactor in the insulin hormone system which regulates blood glucose levels.
• Copper. This is important in the formation of haemoglobin so that among the symptoms of copper
deficiency is anaemia.
• Zinc. This is found in many enzyme systems and is important in the metabolism of glucose.
76
In what ways can we measure the rates of a reaction?
*measure volume of gas evolved over time
*measure change in mass over time
*measure concentration of acid by sampling at intervals
and titration
*measure change in colour over time with a colorimeter
*use iodine clock technique/or use colorimeter
77
Give a brief description of the iodine clock.
This method is used where the reaction produces iodine.
Included in the reaction mixture is a small but constant amount of sodium thiosulphate and some starch indicator.
When the reaction begins the first iodine that is formed reacts with sodium thiosulphate
2S2O3^2-(aq) + I2(aq) --> S4O6^2-(aq) + 2I^-(aq)
and only when the thiosulphate is used up does the iodine produce the dark blue colour with starch.
The time (t) taken from mixing the reactants to the formation of the dark blue starch complex gives a measure of the initial rate of reaction.
78
What does an increase in temperature do to the molecules to increase the rate of a reaction?
This can be explained in terms of the fraction of molecules having energy equal to, or greater than, the activation energy for the reaction.
79
What effect does increasing the temperature have on the rate of a reaction in equilibrium?
For an equilibrium, an increase in temperature increases the rates of both the forward and reverse reactions. This means that equilibrium is attained more quickly but the effect on the position of equilibrium cannot be determined from kinetic data.
80
In terms of entropy what is meant by the disorder of the particles?
the freedom possessed by the molecules or atoms within the system
81
What does kinetic data show us?
Kinetic data tells us how fast a reaction proceeds.
82
What does equilibrium data show us?
Equilibrium data tells us how far a reaction goes.
