Chem5 Transition Metals

Front 1

What is a transition metal?

Back 1

A metal that forms one or more stable ions with a partially filled d sub-shell

Front 2

Why are zinc and scandium not transition metals?

Back 2

Zn forms Zn2+ ion which has a full d sub-shell

Sc forms Sc3+ which has an empty d sub-shell

Front 3

What is the colour of V2+

Back 3

violet

Front 4

What is the colour of V3+?

Back 4

Green

Front 5

What is the colour of VO(2+)?

Back 5

blue

Front 6

What is the colour of VO2(+)?

Back 6

yellow

Front 7

What are the physical properties of transition metals?

Back 7

High melting and boiling points

High density

similar ionic radii

Front 8

What are the chemical properties of transition metals?

Back 8

Form complex ions

Form coloured ions

make good catalysts

have variable oxidation states

Front 9

What is the colour of Ni2+?

Back 9

green

Front 10

What is the colour of Mn2+?

Back 10

pale pink

Front 11

What is the colour of MnO4-?

Back 11

purple

Front 12

Why do transition metals have variable oxidation states?

Back 12

Energy levels of the 3d and 4s subshells are close to one another, so diff number of electrons can be lost using similar amounts of energy

Front 13

What is a complex ion?

Back 13

A central transiiton metal ion surrounded by co-ordinately bonded ligands

Front 14

What is a ligand?

Back 14

A species that forms a co-ordinate bond with a central metal ion

Front 15

What is the bond angle in a:

tetrahedral complex

octahedral complex

square planar complex?

Back 15

109.5

90 (and 180)

90

Front 16

Why are EDTA complexes more stable?

Back 16

Central ion held firmly by many co-ordinate bonds

Front 17

Why are cyanide ions in a metal complex not dangerous?

Back 17

Strongly bound to metal ion

Front 18

What are the uses of EDTA?

Back 18

Antitode to metal poisoning - trap and remove metal ions

remove calcium ions from blood during transfusions to prevent clotting

remove calcium ions from hardwater to prevent clogging of pipes

Front 19

What is the role of haemoglobin?

Back 19

Transport oxygen around the body in the blood

Front 20

Describe the structure and function of haemoglobin?

Back 20

Central Fe2+ ion

4 co-ordinately bonded nitrogen atoms from a porphydrin molecule

also coordinately bound globin molecule (protein)

In lungs, oxygen forms a weak co-ordinate bond forming oxyhaemoglobin

where needed, oxygen displaced by water to form deoxyhaemoglobin

Front 21

Why do transition metal complexes have colour?

Back 21

Absorb particular wavelengths of light

d electrons excited to a higher energy d orbital

remaining wavelengths reflected

wavelength absorbed dictated by energy gap between d orbitals when d-d splitting occurs

Front 22

Why does Sc3+ not have a colour?

Back 22

No electrons in d orbitals to excite

no wavleengths absorbed

Front 23

Why does Zn2+ not have a colour?

Back 23

No vacant d orbital for a d electron to be exicited

Front 24

How can spectrometry be used to determine the conc of a complex ion solution?

Back 24

Pass white light through a filter

Pass filtered light through the sample and a colorimeter

Produce calibration graph using samples of known conc (straight line as absorbance is prop to conc at low concs)

compare absorbance with graph

Front 25

What are the advantages of spectrometry?

Back 25

Easy to take many readings and can determine conc quickly

doesn't use up sample/interfere with reactions

Front 26

How can you reduce dichromate ions and what is the product

Back 26

zinc and dilute hcl

green Cr3+ ions

Front 27

How can you reduce Cr3+ ions and what is the product?

Back 27

zinc and hcl in an inert atmosphere

as blue Cr2+ is unstable

Front 28

How can you oxidise Cr3+ ions? What is the product?

Back 28

hydrogen peroxide in alkaline conditions

yellow CrO42- ions

Front 29

Why, when orange dichromate ions are reduced, is the solution not violet (the colour of [Cr(H2O6]3+)?

Back 29

Ligand substitution occurs by chloride ions in dilute HCl used to reduce

Front 30

How do you prevent oxidation of something?

Back 30

Stablilise through the addition of acid

Front 31

Why do you have to store Fe2+ ions in acidic solution?

Back 31

Prevent oxidation

Front 32

Why do you need dilute acid for reduction of dichromate ions?

Back 32

Enough H+ ions for all dichromate to be reduced

Front 33

Why do transition metals make good catalysts?

Back 33

Variable oxidation states

transfer electrons to speed up reactions

Front 34

How do heterogenous catalysts speed up rate of reaction?

Back 34

Reactants adsorb onto surface of the catalyst;

reactants held in position/in higher conc on surface so more likely to be a successful collision;

weakens bond/leads to fragmentation and lowers activation energy

Front 35

Why is catalyst poisoning expensive?

Back 35

Less product produced as slower rate of reaction

catalyst has to be replaced

Front 36

Describe 3 reactions that use a heterogenous catalyst

Back 36

N2 + 3H2 ----> 2NH3 (Fe(s) catalyst)

SO2 + O2 ---> SO3 (V2O5)

H2 + CO ----> CH3OH (Cr2O3)

Front 37

What determines the suitability of a catalyst to a reaction?

Back 37

How strongly adsorbed reactants are

too strong and prodcut not released

too weak and reaction cant take place

Front 38

What poisons the catalyst in a catalytic converter?

Back 38

Lead

Front 39

What poisons the catalyst in the Haber process?

Back 39

sulfur

Front 40

How do homogenous catalysts work?

Back 40

Produce intermediate species/provide alternative reaction route

of lower activation energy

Front 41

How do you reduce catalyst poisoning?

Back 41

Purify the reactants

Front 42

Why is the reaction between peroxidisulfate nad iodide slow?

Back 42

repulsion between negativ eions

unlikely colision

Front 43

How can you test for the presence of iodine?

Back 43

starch

Front 44

What is meant by autocatalysis?

Back 44

Product of a reaction acts as the catalyst