REDOX/TRANSITION METALS

Question 1

What is a transition metal

Answer 1

Forms at least one stable ion with partially filled d sub shell

Question 2

What key features do transition metals have

Answer 2

Form complex ions
Coloured ions
Catalytic properties
Variable oxidation states

Question 3

Define a coordinate bond

Answer 3

Shared pair of electrons which have both come from the same atom

Question 4

What is a ligand

Answer 4

An ion or molecule with a pair of electrons which can form a coordinate bond with a transition metal ion

Question 5

What is a Bidentate ligand

Answer 5

Molecule with two atoms with pairs of electrons available to form coordinate bonds with transition metal ion eg C2O4

Question 6

What’s a complex ion

Answer 6

Central atom or ion surrounded by lignands

Question 7

What’s a coordinate number

Answer 7

Number of coordinate bonds a transition metal ion can make

Question 8

What is a multidentate ligand

Answer 8

Each ligand forms two or more coordinate bonds

Question 9

What are the four common shapes transition metal complexes form

Answer 9

Octahedral eg [Cu(H2O)6]2+
Tetrahedral eg [CuCl4]2-
Square planer eg [Pt(NH3)2
Linear eg [Ag(H2O)2]+

Question 10

Ligand substitution reaction example
Show how the complex [Cu(H20)6]2+ can be converted into [Cu(H2O)3(NH3)3]2+

Answer 10

[Cu(H2O)6]2+ + 3NH3 -> [Cu(H2O)3(NH3)3]2+ + 3H2O

Question 11

When does the chelate effect occur

Answer 11

When a monodentate ligand is substituted out by a multi or Bidentate ligand

Question 12

Cisplatin as cancer treatment

Answer 12

Binds to DNA in cancerous cells
Prevents DNA from unwinding so cancer cell can not replicate
Prevents growth and spread
Two Cl- ions on cisplatin substitute two N atoms on adjacent guanine bases

Question 13

Why are transition metals coloured

Answer 13

Transition metal have a partially filled d sub shell
These electrons absorb specific amount of energy from visible light and transmits the rest
Electron d sub shell electrons become excited move from ground stable state to excited unstable state

Question 14

Roy and biv

Answer 14

Small e Roy - smaller energy waves, longer wavelength
big e biv- higher energy waves, short wavelength

Question 15

Changes that can alter the colour of compounds

Answer 15

Change in ligands
Change in oxidation state
Change in coordination number
Change in shape

LOCoS

Question 16

Oxidation is….

Answer 16

Loss of electrons

Question 17

Reduction is……

Answer 17

Gain of electrons

Question 18

What is a oxidising agent

Answer 18

Accepts electrons
Its being reduced

Question 19

What is a reducing agent

Answer 19

Loses electrons
Its being oxidised

Question 20

Degine oxidation state

Answer 20

Number assigned to atomd in a compund to follow which elements are gaining ir losing electrons in a reaction

Question 21

Oxidising state of
H
G1 metals
G2 metals
Al
O
F
Cl

Answer 21

H: +1
G1: +1
G2: +2
Al: +3
O: -2 (unless peroxide (H2O2) or bonded wiv F)
F: -1
Cl: -1 ( +1 if bonded with F or O)

Question 22

How to find concentration of an unkown sample from the calibratrion curve(3marks)

Answer 22

Measure abosorbance for a randfe of known concentration
Plot a graph of absorbance against concentration against cruve
Read the value of the concentration for the measured absorbance from the graph

Question 23

Heterogeneous catalyst

Answer 23

Catalyst is in a different phase to the reactant

Question 24

Homogeneous catalyst

Answer 24

Catalyst in the same phase as reactant

Question 25

Mechanism of heterogeneous catalysis (3marks)

Answer 25

Reactant adsorb onto surface of the catalyst on an active site
Reaction accurs on the surface of the catalyst
Products desorb from the surface of the catalyst

Question 26

Making catalysts more efficient

Answer 26

Increase surface area
Spread the caatlyst over an inert support medium

Question 27

Why cant catalyst last forever

Answer 27

Impurities blick active site
Prevents reactant from adsorbing
Purifying the reactant is the best way to prevent poisoning

Question 28

Heterogeneous catalyst equations + catalyst
1. Making Ammonia in the Haber Process
2. Making Sulfuric Acid in the Contact Process
3. Manufacture of Methanol

Answer 28

1. N2(g) + 3H2(g) <———-> 2NH3(g)
   Catalyst- IRON
   2.
   SO2(G) + V2O5(S) <———> SO3(G) + V2O4(S)
   2V2O4(S) + O2(g) <———>2V2O5(S)
   Overall equation: 2SO2(G) +O2(G) ——-> 2SO3(G)
   Catalyst- Vandium(V) oxide
2. CH4(G) + H2O(G) ——> CO(g) +3H2(g)
   CO(G) + 2H2(g) ——> CH3OH(G)
   Catalsyt- chromium (III) oxide (Cr2O3)

Question 29

Homogenous catalyst equations

Answer 29

S2O8 2- (AQ) + 2I-(AQ) ——>2SO4 2- (AQ) + I2(AQ)
2 step porcess
S2O8 2-(AQ) + 2FE2+(AQ) ——-> 2SO4 2-(AQ) + 2FE3+ (AQ)
28-(AQ) + 2FE3+(AQ) ——> I2(aq) +2FE2+HAQ)

Question 30

Autocatakysys mechanism (4 marks)

Answer 30

Rate start off slow as no catalyst present
2 negatively charged reactant collide with very high Ea
As Mn2+ formed rate increases as the reaction is bejng increasingly catalysed
Rate then decreases and levels off as the reactant get used up

Question 31

Autocatalysis equation

Answer 31

2MnO4- + 16H+ +5C2O4 2- —-> 2Mn2+ +8H2O +10CO2