Module 5-Physical Chemistry and Transition Elements Flashcards
(106 cards)
1
Q
If a reactant is first order what will its effect be on the reaction rate?
A
If it is doubled it will double, tripled it will triple etc. (factor x^1)
2
Q
If a reactant is second order what will its effect be on the reaction rate?
A
Increase by a factor of x^2 i.e. if it is doubled rate will quadruple, tripled it will be 3^2.
3
Q
How would you calculate overall order?
A
Add the orders of those present in the rate equation.
4
Q
What is the effect on the reaction rate of a change in concentration of a zero order reactant?
A
Nothing.
5
Q
What is continuous monitoring?
A
Taking continuous measurements throughout the course of the reaction.
6
Q
What does the concentration-time graph look like for a zero order reactant?
A
A straight line with a negative gradient where gradient=k.
7
Q
What does the concentration-time graph look like for a first order reactant?
A
Downward curve with a decreasing gradient over time and a constant half-life (exponential decay).
8
Q
What does the concentration-time graph look like for a second order reactant?
A
Also a downward curve but steeped at the start and leveling off more slowly.
9
Q
How would you calculate k for a FIRST ORDER reaction using the half-life?
A
ln2/t1/2(half-life)
10
Q
How would a rate-concentration graph look for a zero order reaction?first?second?
A
Rate=k so y intercept=k and is a line of y=a number.
Straight line graph through the origin k=gradient.
Upward curve with an increasing gradient (k cannot be directly obtained due to the increasing gradient).
11
Q
How would you calculate k for a second order reaction starting with a rate-concentration graph?
A
Cannot be directly obtained so plot a graph of rate against concentration squared will produce a straight line through the origin from which the gradient would give k.
12
Q
What are clock reactions and what are their purpose?
A
A way of obtaining an initial rate estimation, time is measure from start of reaction until a visual change occurs. Provided there is no significant change in rate during this time, temp’ remains constant and provided the reaction hasnt gone too farit can be assumed that the average rate over this time is the same as the initial rate which is proportional to 1/t.
This is repeated at differing concentrations to calculate experimental values of 1/t for each run.
13
Q
Give an example of a common clock reaction.
A
Iodine, usually mixed with starch to form deep blue colour.
h2o2 added to iodide in acidic conditions, sodium thiosulphate added, when sodium thiosluphate has fully reacted with iodine produced there will be an excess of iodine hence blue colour will appear and reaction is complete.
14
Q
How accurate are clock reactions?
A
Approximation, however, is reasonably accurate provided less than 15% of the reaction has ensued.
15
Q
What is the rate-determining step?
A
The slowest in the reaction mechanism.
16
Q
The effect of temperature on rate constants. Why?
A
It will increase (for every 10 degree rise k doubles).
This is because increasing temp’ shifts Boltzmann to the right increasing the proportion of particles exceeding Ea, as energy increases the particles will also collide more frequently. (mainly determined by Ea though as collision frequency effect is relatively small)
17
Q
What is the Arrhenius equation?
A
the exponential relationship between k and temperature which also includes the frequency (pre-exponential) factor and Ea.
k=Ae^-Ea/RT
18
Q
With heterogenous equilibria what is omitted?
A
Solids and liquids which are seen as effectively constant
19
Q
Mole fraction=
A
Number of mole of the gas/total number of moles in gas mixture
20
Q
Partial pressure=
A
Mole fraction x total pressure
21
Q
Define a transition element.(1)
A
A d block element that can form at least one stable ion with an incomplete d subshell.
(Zn and Sc aren’t!)
22
Q
Why do transition elements make good catalysts?(2)
A
Variable oxidation states mean they can easily transfer electrons hence speed up the reaction
Can also adsorb reactants onto surface.
23
Q
Negatives of transition element uses?(1)
A
Usually toxic eg copper exposure long term leads to kidney and liver damage whilst manganese leads to psychiatric problems.
24
Q
Give examples of transition element catalysts.(2)
A
Fe in Haber process
CuSO4 in zn with acid.
25
Copper(II) reaction with sodium hydroxide, colour change.
What does it form with excess NH3?What is this reaction?
Pale blue solution to blue ppt
With excess the Cu(OH)2(H2O)4 (s) formed goes to [Cu(NH)4(H2O)2]2+ (aq) which is dark blue
A partial ligand substitution reaction.
Both are octrahedral
26
Iron(II) colour change with NaOH or NH3.(2)
Pale green solution to green ppt which darkens.
[Fe(H20)6]2+ + 2NH3 —> [Fe(OH)2(H20)4] (s)
27
Iron(III) + NaOH/NH3 colour change
| Give NH3 equation.
Yellow solution to an orange ppt which darkens with colour
[Fe(H20)6]3+ + 3NH3 —> [Fe(OH)3(H20)3] (s)
28
Manganese(II) colour change with NaOH/NH3, give NH3 equation.
I pale pink solution to pink ppt which darkens.
29
Chromium (III) colour change with NaOH, excess NaOH and NH3.What complexes are formed?(3)
Green solution to grey-green/ppt. Of [Cr(OH)3(H20)3] in excess this reacts further to form Cr(OH)6^3- which is dark green
On addition of excess ammonia this then further reacts to form purple [Cr(NH3)6]3+(aq)
30
Define a complex ion.(1)
A complex ion is a metal ion coordinately bonded to and surrounded by ligands.
31
What is a ligand?
Something which donates a pair of electrons to the central metal ion/atom.
32
What is a monodentate ligand?
One lone pair to donate.
33
What are bidentate ligands?
Two lone pairs to donate to the metal ion.
34
What are multidentate ligands?
Two or more coordinate bonds can be formed meaning the ligand is multidentate.
35
What is the coordination number?
The number of coordinate bond that are formed with the central metal atom/ion.
36
Shape of:
6 coordinate bonds
4 coordinate bonds.
(3)
Octrahedral
| Tetrahedral OR square planar.
37
What is optical isomerism?when does it happen?
A type of stereoisomerism when an ion can exist in two non-superimposable mirror images.
Happens when in octrahedral complexes when 3 bidentate ligands are attached to the central ion (happens with [Ni(en)3]2+.
38
What is cis platin and what is its use?(8)
Anti cancer drug
Pt with two NH3 and 2 Cl bonded in a square planar arrangement
How it works
Chloride ligands displaced by nitrogen atoms on DNA molecule preventing dna replication on the cancerous cell, causing cell death as it is unable to repair damage to the cell
Downside is that it prevents this for normal cells resulting in a suppressed immune system and damage to the kidneys is common.
39
Define the standard enthalpy change of atomisation.(1)
Enthalpy change that takes place for the formation of one mole of gaseous atoms from the element in its standard state under standard conditions.
40
Define lattice enthalpy. What is it a measure of?(2)
The enthalpy change that accompanied the formation of one mole of an ionic lattice from its gaseous ions under standard conditions.
Ionic bond strength, the greater the lattice enthalpy the weaker the bonds, the more negative a lattice enthalpy value the stronger the bonds.
41
Define the first electron affinity.(1)
The energy required to gain one electron by each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions.
42
Define standard enthalpy change of solution.(1)
The enthalpy change that ensues when one mole of solute dissolved in a solvent, if the solvent is water the ions will finish up being surrounded by water molecules as aqueous ions.
43
What does H+(AQ) really represent?(1)
The hydronium ion, H3O+
44
What is special about conc’ HNO3?(1)
Strong oxidising agent.
45
What is special about sigfigs when it comes to pH values?(1)
The sigfigs only start after the decimal point as the whole number before is the logarithmic way for showing powers of 10, unless stated otherwise usually give pH to 2 d.p.
46
In weak dibasic and Tribasic acids, with each subsequent dissociation does pKa increase or decrease?What does this tell you about the strength of the acid?(2)
pKa increases and Ka decreases meaning acid becomes weaker with each dissociation.
47
What approximation do you use to calculate the concentration of a weak acid at eqm using its initial concentration?(2)
Initial conc-H+ conc.
Seeing as those dissociation is small you assume the conc at the start is the same as at eqm
Breaks down for very dilute solutions and for stronger acids (Ka>10^-2) as the difference between HAeqm and HAintial-H+eqm becomes significant.
48
What assumption do you make when calculating Ka about the concentration of H+ and A-?When does this breakdown?(2)
That they are the same at equilibrium (the acid dissociated into equal parts and despite there being some additional H+ due to dissociation of water this is tiny so is neglected)
For very dilute solutions or very weak acids (pH>6) as water will become significant.
49
The simple dissociation of water, H2O—> OH- + H+ is a simplification of what equation?(1)
2H2O—> H3O+ + OH-
50
Kw=[H2O]x?=?
What is its importance?
Ka.
[H+]x[OH-]. (aq)
Sets up the neutral point on the pH scale, controlling H+ and OH- conc in aq, is 1x10-14 at 298K.
51
What is a dibasic base?What does this mean for calculation pH?(2)
One which releases two moles of OH- ions
This means that the conc of the base x2 =OH- conc.
52
When is a buffer most effective?What is the usual operating range of a buffer?(2)
When HA conc is equal to conc of A- (conjugate base)
Range of 2 typically (+/-1 from pKa value of the acid)
Eg if pKa is 5 the pH range would typically be 4-6.
53
What is the pH range for blood plasma and what buffer system is responsible for its maintenance?What happens if you fall below or above this range?(4)
Carbonic acid-hydrogen carbonate buffer solution maintains it between 7.35-7.45
H2Fao3/HCO3-
Below, acidosis which causes fatigue, shortness of breath and in extreme cases death
Above, alkalosis which causes muscle spasms, light-headedness and nausea.
54
Explain how you would obtain a pH titration curve.How could you improve this?(5)
- add pipette to pipette acid into a conical flask and add base to burette
- add base 1cm3 at a time recording pH using a pH meter (an electrode connected to a meter which displays the reading) by placing the electrode into the conical flask, after each addition swirl the contents Nd total the volume of base used
- continue this until pH starts to change more rapidly in which case add the base dropwise for each reading until it slows again
- continue adding 1cm3 again until an excess of base has been added and the pH reading remains constant/shows little change for several additions.
Could use data logger and magnetic stirrer so graph could automatically be drawn using the correct computer software.
55
What is the point on a pH titration curve called when the volumes have exactly reacted with one another?(1)
The equivalence point.
56
What is an indicator?How does this allow it to work?What is its range usually and how do you choose the best indicator?(4)
It is a weak acid, in acidic conditions it is in the acid state and in alkali it is in the conjugate base state
These two have distinctive colour changes which can be detected.
Over 2 pH units, ideally equivalence point and end point would be the same, needs to cover vertical section.
57
What two things are said for the end point of a titration?(2)
[HA]=[A-]
Ka=[H+] therefore pKa of HA=pH of end point
58
Why are Sc and Zn not classed as transition elements?(2)
Don’t form at least one stable ion with an incomplete d subshell
Sc3+ is only Sc ion formed and this has an empty 3d subshell
Zn2+ is the only Zn ion corned and this has a complete 3d subshell
59
Give varying oxidation states of chromate ions and their colours.(2)
Cr2O7- (Cr=+6) orange
| Cr3+ green.
60
Give varying oxidation states of manganese ions and their colours.(3)
MnO4- (Mn=+7) purple
MnO4^2- (Mn=6) green
Mn2+ pale pink
61
Give varying oxidation states of Vanadium ions and their colours.(4)
VO2^+ (+5) yellow
VO^2+ (+4) blue
V3+ green
V2+ violet
62
Give varying oxidation states of titanium ions and their colours.(2)
Ti3+ purple
| Ti2+ violet.
63
Give the colours of cobalt and nickel ions and their colours.(2)
Co2+ pink
| Ni2+ green.
64
Give examples of common monodentate ligands.(4)
Which one of these is bigger out of them all and what does this mean?(1)
CN-, Cl-, H20, NH3
Cl-, bigger so firms tetrahedral arrangement rather than octrahedral.
65
What common bidentate ligand is there?What is its role in optical isomerism?(2)
Ethane-1,2-diamine (NH2CH2CH2NH2) also referred to as ‘en’.
3 of these bidentate ligands attaches to metal such as nickel results in optical isomers, octrahedral shape.
66
What is interesting about [Cr(H20)6]3+?Give the ligand substitution reaction equation for it reacting with NH3.(2)
It is violet but in practise it appears green.
[Cr(H20)6]3+ + 6NH3 —> [Cr(NH3)6]3+ + 6H20
Violet (green) to purple
Both octrahedral as ligands are similar sizes.
67
Write the equations for the reaction of complex ion of hexa-aqua copper (II) with Cl-, what is special about this reaction?Note any colour changes.(3)
Ligands are different sizes so go from octrahedral to tetrahedral (pale blue to yellow)
[Cu(H20)6]2+ + 4Cl- —> [CuCl4]2- + 6H20
68
Explain the biochemical importance of iron in haemoglobin (to do with ligand substitution of both O2 and CO).(4)
Fe2+ complex with 6 coordinate bonds, 4 from N atoms within circular molecule called harm
5th comes from nitrogen on globin protein
H20 bond to 6th but in lungs this is subbed for O2 forming oxyhaemoglobin, reverse happens at tissues
If CO present this subs instead forming carboxyhaemoglobin, CO don’t wanna leave nd this is irreversible as O2 can no longer be transported.
69
What is used to convert Fe2+ to Fe3+, write the half equations and mention colour change.What type of reaction is this?(4)
Acidified potassium manganate (VII), oxidation of Fe reduction of KMnO4-REDOX
Pale green to yellow
MnO4- + 8H+ + 5e- —> Mn2+ +4H20
Fe2+—>Fe3+ + e-
70
What is used to reduce Fe3+ to Fe2+?Write half equations Nd State colour change.(4)
Iodide ions, yellow to pale green
Iodide ions oxidised, Fe reduced.
Fe3+ + e—-> Fe2+
2I- —-> I2 + 2e-
71
How do you convert Cr3+ in [Cr(OH)6]3- to Cr6+ in CrO4- (chromate)?What is the colour change?How do you then get to Dichromate ions?How do you get back to Cr3+?State any colour changes.(5)
Warming with H202 in alkaline conditions
Dark green to yellow.
Chromium is oxidised O2 is reduced.
Add dilute H2S04 produces dichromate ORANGE
then reversed with acidified Zn to Cr3+ GREEN. Zn is oxidised m, chromate reduced.
72
What is used to reduce Cu2+(aq), What is formed?(2)
Iodide ions, white ppt of CuI2 (s) and I2 (aq)
73
What happens to Cu+ (aq) and why?(2)
Unstable to spontaneously disproportionately to produce Cu(s) and Cu2+ (aq).
74
What are the only things you can add to a redox half equation to balance it?(3)
Electrons
Protons (H+)
H20.
75
When trying to find out how many MnO4- ions are needed to oxidise completely a reducing agent what do you need to do?(3)
Titration placing acidified (adding excess H2SO4) reducing agent eg Fe3+ in conical flask and MnO4- in burette adding dropwise towards rough titre the end
Wait for drop that changes colour ie end point, repeat until you get concordancy/3 times (not including rough titre) and calculate mean titre.
76
What is the use of a Iodine-Sodium Thiosulphate titration?(1)
A way of finding the concentration of an oxidising agent, eg potassium iodide (V)
77
What are the two stages in a iodine-thiosulphate titration?(2)
Use a sample of oxidising agent to oxide iodide as much as possible (add known volume of potassium iodate (V) to excess of KI this will form iodine
Find out how many moles of iodine have been produced by titration great with sodium thiosulphate (when iodine turns pale yellow the end point is nearing so add starch (turns dark blue) this way clear end point will be seen-add dropwise.
Use these moles to calculate the concentration of the oxidising agent.
78
What is the cell potential/e.m.f/Ecell?(1)
The voltage between two half cells.
79
Describe how you would set up a electrochemical cell for:
Two metals
Aqueous metal ions of the same element in varying oxidation states
For non metals.
(4)
All connected by a salt bridge soaked in KNO3 which allows the flow of ions and balance out charges
- two metals with metal electrode dipped into aqueous ions of the metal
- aqueous ions eg Fe2+ and Fe3+ with platinum electrode (used as inert and conducts)
- in has eg chlorine gas it can be bubbled over a Pt electrode sitting in a solution of its aqueous ions, in this case Cl-.
80
What does the E• (electrode potential) say about a particular half equation?How is it calculated?(2)
More likely to be reduce the higher the E• (• means under standard conditions)
More postive E•-more negative E•.
81
Define the standard electrode potential, E•.How is a standard hydrogen electrode set up?(2)
The E• of a half cell is the voltage measure under standard conditions when the half-cell is connected to a standard hydrogen electrode where the hydrogen electrode is always on the left hand side.
H2(g) pumped in, Pt electrode, H+ 1M (aq)
82
What are the standard conditions for E•?What does this allow?(4)
- any solutions must be 1moldm-3 or equinoxes
- 298k
- 100kPa.
For E• valued to be controlled
83
How do you determine feasibility of a reaction using E•?(1)
Determine which way the half cells would combine and determine whether that matches the reaction eg
Half equation for copper =+.34V
For H2 is 0V
Determine whether copper would react with H2SO4
No as equations would should copper ions reacting with H2 gas which wouldn’t be the same therefore not feesible.
84
Why might the prediction of feasibility using E• be wrong?(4)
-Kinetics May be unfavourable eg Too high an Ea or too slow a rate to observe reaction
-non standard conditions:
If conc of one is increased or decreased this would effect E• eg if the more reactive metal is increased in conc ( one with lower E• therefore is oxidised) this will shift eqm to the left causing more oxidation (great electron loss) therefore a E• of the metal will become less negative so whole cell potential will be lower.
Alternatively, if conc of the oxidising metal (less reactive therefore higher E• as itself reduced) is increased this will cause eqm to shift right hence increasing the electrode potential for the metal and leading to an overall higher E• for the whole cell.
85
What is an energy storage cell?(1)
A battery, works like an electrochemical cell.
86
What’s the difference between a primary and secondary modern storage cell, give examples of some in use.(2)
Primary are non-rechargeable eg wall clocks
| Secondary are rechargeable eg lithium ion cells in laptops, phone chargers or lead acid batteries in car batteries.
87
Advantages a disadvantages of electrochemical cells.(4)
-limited by products unlike combustion, in Hydrogen fuel cell only water as by product
-more efficient as don’t give off heat as wasted energy like combustion
However
Lithium ion batteries are highly reactive Nd flammable if overheated
Toxic chemicals used which have to be disposed of after use.
88
What is a fuel cell?What is part of a hydrogen fuel cell, in each type?(3)
Fuel cell produced fuel by reacting a fuel with an oxidant, namely oxygen.
Acid hydrogen fuel cell, o2 and fuel fed in H+ is electrolyte and H20 leaves, at anode H2 is split and electrons travel around circuit to cathode whilst H+ can travel across polymer electrolyte membrane (PEM)
The H+ e- and O2 combine to form water.
1.23V is the E• value
Alkali hydrogen fuel cell uses same principle but slightly different as OH- reacts with H2 to make water.
89
What is a reactant order?What is overall order?(2)
It tells you the effect of the concentration of a reactant on a reaction rate.
The sum of all of the orders in a particular reaction.
90
If the overall order of a reaction is 1 how can you calculate its rate constant from a rate-concentration graph?(1)
Calculate the gradient of the graph, as k=rate/[X]^1.
| the bigger k is the faster the reaction, where k is at a particular temperature!
91
What is the half-life?(1)
The time taken for the concentration of a reactant to half, this remains constant for first order reactants regardless of their concentration (i.e. they have a constant half life)
92
What should be remembered when proposing a reaction mechanism from a rate equation and vice versa?(3)
catalysts can be in the rate equation and hence in the RDS
Just because a chemical equation has a balancing number in-front of it does not mean this is the order, this can only be determined experimentally
-the RDS doesn't have to be the first step.
93
What do you need to remember when you are working out A and Ea from an Arhennius plot?(2)
Do e^of your value, remeber your y intercept=lnA therefore to get just A need to do inverse of ln (e).
Gradient is equal to -Ea/R so multiply gradient by -R.
94
What do you omit from a Kc/Kp expression if it is a heterogeneous reaction?What is the exception to this?(2)
Solids and liquids, however, if the solvent isnt aqueous you need to include any water involved in the expression.
95
If in an equation two products have the same stoichiometry, what does this tell you about their partial pressures?(1)
They are the same.
96
What is the effect of the following on Kc/Kp:
Temperature
Pressure concentration. (2)
Temp can effect Kc/p depending on the type of reaction and whether it is increased or decreased.
Pressure and conc' cannot, yes these effect amounts at equilibrium but this is as a direct consequence of keeping Kc/Kp constant as the eqm shifts to restore the ratio of Kc/Kp
97
Define the enthalpy of hydration.(1)
Is the enthalpy change when 1 mole of gaseous ions dissolves in water.
98
What affects lattice enthalpy?Explain both factors.(
- Ionic charge-the greater the ionic charge the stronger the electrostatic forces of attraction between the cations and anions therefore a more exothermic lattice enthalpy, /_\leH value
- Ionic radius/ion size-the smaller the ionic radii the higher the charge density therefore the greater the electrostatic forces of attraction, also means ions can pack closer together which both result in stronger forces of attraction and therefore a more exothermic lattice enthalpy value.
99
From a Born-Haber cycle /_\leH is equal to...(1)
/_\f- the sum of the rest (inc. atomisation energy, IE(s), EA(s)
100
When is it that a substance tends to dissolve?What does this mean is usually the case for enthalpies of solution of soluble substances?(2)
When the energy released is roughly the same as, or greater than, the energy taken in
Means a more exothermic enthalpy of solution value.
101
From a Born-Haber cycle, how would you calculate lattice enthalpy?(1)
/_\solH- sum of /_\hydH (hydrations).
102
What factors affect the enthalpy of hydration?Explain them.(2)
- Ionic charge-the greater the ionic charge the greater the electrostatic forces of attraction between the ions and the water molecules therefore more energy is released in bond making hence a more exothermic /_\solH value
- ionic radii/size of the ions-higher charge density therefore greater electrostatic forces of attraction between the water molecules and the ions and hence greater energy released in bond formation therefore a more exothermic /_\solH value.
103
What is entropy?What does a higher entropy value mean and how do you calculate entropy change?(3)
The number of ways particles can be arranged and the number of ways energy can be shared out amongst particles, the greater the enthalpy the more disorder
remember SOI (/_\S=Out-In)
104
What two factors affect entropy?(2)
Physical state
| no of moles/particles.
105
What does the entropy say about a substances thermodynamic feesibility?(2)
The more disorder (higher entropy) the more stable, this explains why some reactions are feasible even if their /_\H is endothermic as they trying to increase entropy.
When a substance has reached its highest entropy state (lowest energy state) the substance is said to be thermodynamically stable therefore will not react without the input of energy.
106
Why does a negative /_\G not guarantee a feasible reaction?(2)
Too high an Ea
| Too slow a reaction rate.
