Redox and electrode potentials and transition metals Flashcards
Define redox
A reaction in which both reduction and oxidation take place.
Define oxidation
The loss of electrons or an increase in oxidation number.
Define reduction
The gain of electrons or a decrease in oxidation number.
what is an oxidising agent?
The oxidising agent:
1) takes electrons away from the atom that is oxidised
2) contains the atom that is reduced
what is a reducing agent?
a reducing agent:
1) adds electrons to the atom that is reduced
2) is itself oxidised
how can redox reactions be written from oxidation numbers?
increase in oxidation number = decrease in oxidation number for another atom
Why is there no clear colour change at the end point of a Vanadium and Potassium Manganate titration?
KMnO(4) is purple/pink
V2+ is violet
What property does the voltmeter have in a cell?
High resistance
Which way does the current flow in the cell?
Negative electrode to the positive electrode
How do the ions flow between cells?
ions flow across the Salt bridge
What is the salt bridge generally made of?
Potassium nitrate (KNO3)
Ammonium nitrate (NH4NO3)
What is the electrode made of in a standard hydrogen cell?
Platinum
What is in the half cell of Fe3+ and Fe2+?
Inert Pt electrode and Equimolar Fe2+ and Fe3+ (1 mol dm^-3)
When two half cells are connected, which is oxidised and which is reduced?
More reactive metal is oxidised
Less reactive metal is reduced
Define standard electrode potential
The emf of a half cell compared with a standard hydrogen half cell, measured at 298K with solution concentrations of 1 mol/dm^3 and a gas pressure of 100kPa.
What is the electrode potential of a hydrogen half cell?
0.00V
What is the electrode potential of the cell?
Electrode potential of the positive terminal minus the electrode potential of the negative terminal
How do we know if a cell is feasible?
If the electrode potential of the cell is positive, the reaction is feasible.
what’s the Eo of a cell equation?
Eo cell = Eo (positive electrode) - Eo (negative electrode)
what are metal/metal ion half cells?
the half cell is a metal rod dipped in a solution of its metal ion
what is an ion/ion half cell?
An ion/ion half cell is a solution containing ions of the same element in different oxidation states
what is electrode potential?
electrode potential, E, is the tendency for electrons to be gained and for reduction to take place in a half cell
how do you measure a standard electrode potential?
To measure electrode potential, the half cell is connected to a standard hydrogen potential.
1) the electrodes are connected by a wire to allow a controlled flow of electrons through a voltmeter
2) The two solutions are connected by a salt bridge
3) The salt bridge contains ions
what does the more negative the Eo value mean?
The more negative the Eo value
1) it’s more likely to lose electrons and undergo oxidation
2) the less the tendency to gain electrons and undergo reduction
What are the two special cases in the d-block in terms of electron configuration?
1) Chromium: 3d5 4s1 instead of 3d4 4s2. Half filled subshell
2) Copper: 3d10 4s1 instead of 3d9 4s2. Full subshell
Why do these special cases exist in the d block electron configurations?
A half filled and a fully filled d sub shell gives greater stability to these atoms.
What are transition elements?
D-block elements that form at least one ion with a partially filled d-orbital.
Which d-block elements are excluded from being transition elements?
Scandium and zinc. scandium forms a sc 3+ ion and zinc forms a Zn 2+ ion.
the zinc is empty and scandium is scant.
What are the properties of the transition elements?
1) transition elements form compounds with different oxidation states.
2) Form coloured compounds
3) Elements and compounds can act as catalysts
what are the colours of the various ions of iron?
iron 2+ - pale green
iron 3+ - yellow
What colours are the various ions of Chromium (Cr) ? what are the colours?
chromium/cr 3+ is green
chromium/cr 6+ is yellow / orange
What colours are the various ions of Copper?
Cu 2+ is blue
Cu + and Cu 3+ is colourless
What colour is potassium dichromate(VI)?
K2Cr2O7 is Orange
What colour is cobalt(II) chloride?
cobalt(II) chloride is Pink-purple
What colour is nickel(II) sulfate (NiSO₄) ?
NiSO₄ is Green
What colour is hydrated copper(II) sulfate?
Blue
What is the catalyst used in the Haber process?
an iron catalyst is used in the haber proccess.
N2 (g) + 3H2 (g) = 2NH3 (g)
What is the catalyst used in the production of sulfur trioxide for the manufacture of sulfuric acid?
Vanadium(V) oxide
V2O5
2SO2 (g) + O2 (g) = 2SO3
What is the catalyst used in hydrogenation?
Nickel
What is the catalyst used in the reaction of zinc metal with acids?
Cu 2+ ions are used as a catalyst in the reaction of zinc metal with acids : Zn (s) + H2SO4 = ZnSO4 (aq) + H2 (g)
What is the catalyst used in catalytic decomposition of hydrogen peroxide?
Manganese(IV) oxide
MnO2
2H202 (aq) = 2H2O (l) + O2
Define what a complex ion is
A complex ion is formed when ligands bond to a central transition metal ion.
Define coordination number
The number of coordinate bonds attached to the central metal ion.
Define what a ligand is
A molecule or ion that can donates a pair of electrons to the central transition metal ion to form a coordinate bond or dative covalent bond.
What is meant by a monodentate ligand?
A ligand that is able to donate one (hence mono) pair of electrons to a central metal ion.
Give 5 examples of common monodentate ligands and their charges
Water, Ammonia, Cyanide, Chorine, Hydroxide
what is a bidentate ligand?
A bidentate (bi = two) ligand donates two pairs of electrons to the central metal ion
Define denticity
The number of separate sites in a molecule or ion that can donate an electron pair to a transition metal ion.
What shape is created from a complex ion having a coordination number of 6?
an Octahedral shape is formed when it has a coordination number of six.
What shapes can be created from a complex ion having a coordination number of 4?
when there is a coordination number if 4 the shape is:
Tetrahedral
OR
Square planar
When is a square planar shape formed in a complex ion?
When the transition metal in the complex ion has eight d-electrons in the highest energy d-sub-shell. e.g platinum (II) and palladium (II)
What is stereoisomerism?
Same structural formula but a different arrangement of the atoms in space.
What are the two types of stereoisomerism?
Cis-trans isomerism
Optical isomerism
when does cis-trans isomerism exist in monodente square planar complexes? what is the general formula?
cis and trans isomers exist in square planar complexes with:
1) two molecules/ions of one monodentate ligand, X
2) two molecules/ions of another monodentate ligand Y
the general formula is [MX2Y2]n (n=charge)
