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Chemistry OCR A > Redox and electrode potentials and transition metals > Flashcards

Redox and electrode potentials and transition metals Flashcards

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1
Q

Define redox

A

A reaction in which both reduction and oxidation take place.

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2
Q

Define oxidation

A

The loss of electrons or an increase in oxidation number.

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3
Q

Define reduction

A

The gain of electrons or a decrease in oxidation number.

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4
Q

what is an oxidising agent?

A

The oxidising agent:

1) takes electrons away from the atom that is oxidised
2) contains the atom that is reduced

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5
Q

what is a reducing agent?

A

a reducing agent:

1) adds electrons to the atom that is reduced
2) is itself oxidised

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6
Q

how can redox reactions be written from oxidation numbers?

A

increase in oxidation number = decrease in oxidation number for another atom

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7
Q

Why is there no clear colour change at the end point of a Vanadium and Potassium Manganate titration?

A

KMnO(4) is purple/pink

V2+ is violet

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8
Q

What property does the voltmeter have in a cell?

A

High resistance

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9
Q

Which way does the current flow in the cell?

A

Negative electrode to the positive electrode

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10
Q

How do the ions flow between cells?

A

ions flow across the Salt bridge

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11
Q

What is the salt bridge generally made of?

A

Potassium nitrate (KNO3)
Ammonium nitrate (NH4NO3)

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12
Q

What is the electrode made of in a standard hydrogen cell?

A

Platinum

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13
Q

What is in the half cell of Fe3+ and Fe2+?

A

Inert Pt electrode and Equimolar Fe2+ and Fe3+ (1 mol dm^-3)

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14
Q

When two half cells are connected, which is oxidised and which is reduced?

A

More reactive metal is oxidised

Less reactive metal is reduced

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15
Q

Define standard electrode potential

A

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.

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16
Q

What is the electrode potential of a hydrogen half cell?

A

0.00V

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17
Q

What is the electrode potential of the cell?

A

Electrode potential of the positive terminal minus the electrode potential of the negative terminal

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18
Q

How do we know if a cell is feasible?

A

If the electrode potential of the cell is positive, the reaction is feasible.

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19
Q

what’s the Eo of a cell equation?

A

Eo cell = Eo (positive electrode) - Eo (negative electrode)

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20
Q

what are metal/metal ion half cells?

A

the half cell is a metal rod dipped in a solution of its metal ion

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21
Q

what is an ion/ion half cell?

A

An ion/ion half cell is a solution containing ions of the same element in different oxidation states

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22
Q

what is electrode potential?

A

electrode potential, E, is the tendency for electrons to be gained and for reduction to take place in a half cell

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23
Q

how do you measure a standard electrode potential?

A

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

24
Q

what does the more negative the Eo value mean?

A

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

25
Q

What are the two special cases in the d-block in terms of electron configuration?

A

1) Chromium: 3d5 4s1 instead of 3d4 4s2. Half filled subshell
2) Copper: 3d10 4s1 instead of 3d9 4s2. Full subshell

26
Q

Why do these special cases exist in the d block electron configurations?

A

A half filled and a fully filled d sub shell gives greater stability to these atoms.

27
Q

What are transition elements?

A

D-block elements that form at least one ion with a partially filled d-orbital.

28
Q

Which d-block elements are excluded from being transition elements?

A

Scandium and zinc. scandium forms a sc 3+ ion and zinc forms a Zn 2+ ion.

the zinc is empty and scandium is scant.

29
Q

What are the properties of the transition elements?

A

1) transition elements form compounds with different oxidation states.
2) Form coloured compounds
3) Elements and compounds can act as catalysts

30
Q

what are the colours of the various ions of iron?

A

iron 2+ - pale green

iron 3+ - yellow

31
Q

What colours are the various ions of Chromium (Cr) ? what are the colours?

A

chromium/cr 3+ is green

chromium/cr 6+ is yellow / orange

32
Q

What colours are the various ions of Copper?

A

Cu 2+ is blue

Cu + and Cu 3+ is colourless

33
Q

What colour is potassium dichromate(VI)?

A

K2Cr2O7 is Orange

34
Q

What colour is cobalt(II) chloride?

A

cobalt(II) chloride is Pink-purple

35
Q

What colour is nickel(II) sulfate (NiSO₄) ?

A

NiSO₄ is Green

36
Q

What colour is hydrated copper(II) sulfate?

A

Blue

37
Q

What is the catalyst used in the Haber process?

A

an iron catalyst is used in the haber proccess.

N2 (g) + 3H2 (g) = 2NH3 (g)

38
Q

What is the catalyst used in the production of sulfur trioxide for the manufacture of sulfuric acid?

A

Vanadium(V) oxide
V2O5

2SO2 (g) + O2 (g) = 2SO3

39
Q

What is the catalyst used in hydrogenation?

A

Nickel

40
Q

What is the catalyst used in the reaction of zinc metal with acids?

A

Cu 2+ ions are used as a catalyst in the reaction of zinc metal with acids : Zn (s) + H2SO4 = ZnSO4 (aq) + H2 (g)

41
Q

What is the catalyst used in catalytic decomposition of hydrogen peroxide?

A

Manganese(IV) oxide
MnO2

2H202 (aq) = 2H2O (l) + O2

42
Q

Define what a complex ion is

A

A complex ion is formed when ligands bond to a central transition metal ion.

43
Q

Define coordination number

A

The number of coordinate bonds attached to the central metal ion.

44
Q

Define what a ligand is

A

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.

45
Q

What is meant by a monodentate ligand?

A

A ligand that is able to donate one (hence mono) pair of electrons to a central metal ion.

46
Q

Give 5 examples of common monodentate ligands and their charges

A

Water, Ammonia, Cyanide, Chorine, Hydroxide

47
Q

what is a bidentate ligand?

A

A bidentate (bi = two) ligand donates two pairs of electrons to the central metal ion

48
Q

Define denticity

A

The number of separate sites in a molecule or ion that can donate an electron pair to a transition metal ion.

49
Q

What shape is created from a complex ion having a coordination number of 6?

A

an Octahedral shape is formed when it has a coordination number of six.

50
Q

What shapes can be created from a complex ion having a coordination number of 4?

A

when there is a coordination number if 4 the shape is:
Tetrahedral
OR
Square planar

51
Q

When is a square planar shape formed in a complex ion?

A

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)

52
Q

What is stereoisomerism?

A

Same structural formula but a different arrangement of the atoms in space.

53
Q

What are the two types of stereoisomerism?

A

Cis-trans isomerism

Optical isomerism

54
Q

when does cis-trans isomerism exist in monodente square planar complexes? what is the general formula?

A

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)

55
Q
A

Chemistry OCR A (13 decks)

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