Developing metals Flashcards
Fill in the gaps
A loss of electrons is _____
A gain of electrons is ______
A reducing agent _____ some of its electrons to ____ something and gets _____ itself
The more powerful a reducing agent is the more easilly it cann be _____ itself
The oxidising agent ____ electrons saway from something to _____ and gets _____ itself
The more powerful an oxidising agent is the more easily it can be _____
Oxidation
Reduction
Donates
Reduce
Oxidised
Oxidised
Takes
Oxidise
Reduced
Reduced
What do you do to ionic half equations to combine and balance them?
Multiply up an cancel out the electrons
If the oxidising agent contains oxygen add H+ and H2O
What are the steps for a redox titration?
1) Measure out your reducing agent (Fe2+) using a volumetric pipette and put in a conical flask
2) Add dilute sulfuric acid in excess (H+ allows the oxidising agent to be reduced)
3) Add the oxidising agent (MnO4-) to the reducing agent using a burette
4) Stop at the first permanent pink colour
Describe the colour change in the redox titration
Manganate ions in potassium manganate are purple
When added to the reducing agent they are reduced to Mn2+ which are colourless
The reaction continues until all the reducing agent has reacted and the one drop too much will turn it pink
Describe and draw an electrochemical cell
Two different metals dipped in salt solutions of their own ions and connected by a wire and a KNO3 salt bridge
Electrons flow from the most reactive metal to the least
Does oxidation/ reduction happen at the anode or cathode?
Oxidation - anode
Reduction - cathode
What is the purpose of the salt bridge?
Complete the cell and balance out charged
Prevents charge from building up
What is the defenition of a transition metal?
forms at least one stable ion with an incompletely filled d orbital
What is the general configuration of a TM?
[Ar] 4sx 3dy
(4s fills and empties before 3d)
What are the TM exceptions and why?
Sc only makes Sc3+ which is a completley empty d orbital
Zn only makes Zn2+ which is a completley filled d orbital
What is the electron config of Cr and Cu and why?
Cr
[Ar] 4s1 3d5
- the 4s electron moves to 3d giving only unpaired electrons so there is less repulsion meaning its more stable
Cu
[Ar] 4s1 3d10
- the 4s electron moves to the 3d making a completely filled subshell which is more stable
What are the 4 characteristic chemical properties of TM?
- Act as catalysts
- Variable oxidation states
- Form coloured compounds
- Form complexes
Why are TM good homogeneous catalysts?
they have variable oxidation states so they accept and loose electrons easilly so can form intermediates
Why are TM good heterogeneous catalysts?
they use 4s and 3d for adsorption
Why do TM have variable oxidation states?
the 4s and 3d subshell have similar energies so there are no big jumps in sucsessive ionisation energy
What is a complex?
a central transition metal ions surrounded by ligands
What is a ligand?
species which donates a pair of electrons to a TM ion to forma dative bond
What describes a ligand which makes one, two or multiple dative bonds and give examples?
One - monodentate (water, ammonia, chlordie, cyanide)
Two - bidentate (1,2 - diamino ethane and ethanedioate)
Many - polydnetate/ hexadentate (6) (edta4-)
How are complexes written?
[TM ion (ligand 1) x (ligand 2) x] overall charge
x = coordination number
Name the shape and bond angle for the complexes if they have a coordination number of 2,4 or 6
2 - linear 180
4 - tetrahedral 109.5 or square planar 90 (rare)
6 - octahedral 90
What is a ligand substitution reaction and when do they occur?
When ligands are swapped for another
Happen if the new complex is more stable or if there is an increase in entropy
Why are complexed coloured?
When ligands surround a TM ions the 3d orbital splits in two sets creating an energy gap which corresponds to visible light this is absorbed to excite electrons from a low d orbital to a high one and the complimentary colour is transmitted
How can you change the colour of a complex?
change the…
TM ion
the oxidation state of the TM ion
the ligand
the coordiation number
What does a colorimeter do?
measures the absorbance of light
How do you prepare a colorimeter?
zero it with water and choose the right filter (the complimentary colour to the solution or which ever gives the highest absorbance)
How do you find the conc of an unknown using a colourimeter?
Make 5 solutions of known conc above and below the unknown
Measure absorbance and plot a calibration curve (absrobance against conc)
Line of best fit should go through (0,0)
How do you find the formula of a TM complex using a colourimeter?
Mix ion with different ratios of ligand 1 and 3
Measure absorbance
Plot a graph with the conc of the two ligands both on the x axis against absorbance
Draw two lines of best fit - where they cross is the perfect ratio
What is the colour of…
[Cu(H2O)6] 2+
Cu(OH)2
[Cu(NH3)4 (H2O)2] 2+
[CuCl4] 2-
blue
blue
dark blue
yellow
What is the colour of…
[Fe(H2O)6] 2+
Fe(OH)2
green
What is the colour of…
[Fe(H2O)6] 3+
Fe(OH)3
orange
What is an elecrode potential?
Gives a measure of the tendancy to loose or gain electrons
What does a positive E cell mean?
better oxidising agent
more easily reduced
forwards reaction occurs
equilibrium lies to the right
What does a negative E cell mean?
better reducing agent
more easily oxidised
backwards reaction occurs
equilibrium lies to the left
What is the purose of the voltmeter in a electrochemical cell?
it is high resistance so few electrons pass so minimal current flows so the conc of the solutions don’t change
What do you use in an electrochemical cell if there is a gas?
platinum flag
How do you calculate standard electrode potential?
Flip the sign of the most negative E value and add them together
Which way do electrons flow in electrochemical cells?
More negative to more positive half cell
Draw the standard hydrogen electrode
What is the standard electrode potential?
the potential different between a half cell and a standard hydrogen half cell under standard conditions
What are the pros and cons for the standard calomel electrode?
Pros
- portable
- no gas involved
Cons
- mercury is toxic
What are the equations invloved in rusting?
O2 + 2H2O + 4e- <—> 4OH-
Fe2+ + 2e- <—> Fe(s)
Describe what happens in rusting at the edge of the water droplet and at the center
1) At the edge
- hight oxygen
- O2 + 2H2O + 4e- –> 4OH-
- Reduction
- Cathode site
2) At the center
- low oxygen
- Fe — Fe2+ + 2e-
- As Fe dissolves a hole forms
- Oxidation
- Anode site
Electrons flow from 2 to 1
What reaction forms green rust and why does it happen?
Fe2+ + 2OH- —> Fe(OH)2
when there isn’t enough oxygen
What is the equation for brown rust and when does it happen?
Fe(OH)2 —> Fe2O3 xH2O
when there is enough oxygen
What increases rusting and why?
Salt - improves conductivity becuase there are more ions
Acidic conditions - (1) decreased OH- so POE shitfs right so less electrons formed (2) causing POE to shift right making more Fe2+
1) O2 + 2H2O + 4e- —> 4OH-
2) Fe —> Fe2+ +2e-
What decreases rusting and why?
Impurities that form precipitates of Fe2+ or OH- due to interference with electrochemical properties
Alkaline conditions - (1) increased OH- so POE shifts left forming more electrons (2) causes POE to shift left making more Fe2+
1) O2 + 2H2O + 4e- —> 4OH-
2) Fe —> Fe2+ +2e-
How do you prevent rusting?
Make a barrier between the iron and the air/ water (paint/oil)
Sacraficial protection - a more reactive metal in replace of iron
Stainless steel - an alloy of iron and chromium
Chromium corrodes in preference to iron and forms a protective oxide layer
Impressed current
