Transition Metal and group 2 Model Answers

Question 1

Method of UV-Visible spectroscopy

Answer 1

Standard solution of known conc is made up
Serial dilutions are made to get at least 5 different known concentrations that range around the unknown concentration
The absorbance of each solution is measured by passing the complementary colour of light through the solution
The absorbance of the unknown solution is measured
A graph is plotted: absorbance vs known conc
Graph is used to determine conc of unknown solution by reading absorbance

Question 2

Properties of transition metals

Answer 2

Form complex ions
Form coloured ions in solution
Have variable oxidation states
Show catalytic activity

Question 3

Complex ion

Answer 3

Central metal ion or atom surrounded by ligands

Question 4

Ligand

Answer 4

Molecule or ion that forms a coordinate bond with a transition metal by donating a pair of electrons

Question 5

Coordination number

Answer 5

Number of coordinate bonds to central metal atom or ion

Question 6

Naming ions: chloride, cyanide, hydroxide, ammonia, water

Answer 6

Chloro cyano hydroxo ammine aqua

Question 7

Which order do ligands come in

Answer 7

Negative then neutral

If same charge, alphabetical

Question 8

Naming ions: copper, manganese, chromium, silver, iron, vanadium, cobalt

Answer 8

Cuprate, manganate, chromate, argentate, ferrate, vanadate, cobaltate

Question 9

When does copper become cuprate?

Answer 9

If ion has overall negative charge

Question 10

Why do transition metals form coloured compounds? (5)

Answer 10

d-subshells split
Electrons absorb visible light and move to higher d-orbital
E=hf
Wavelengths not absorbed are transmitted or reflected

Question 11

How does haemoglobin enable oxygen to be transported in the blood?

Answer 11

Oxygen forms co-ordinate bond to Fe(II) in haemoglobin

Question 12

Linear complex example

Answer 12

[Ag(NH3)2]

Question 13

Tetrahedral complex example

Answer 13

[CoCl4]2-

Question 14

Square planar complex example

Answer 14

[PtCl2(NH3)2]

Question 15

Method for UV-visible spectroscopy

Answer 15

Make up 5 solutions of known concentration
Measure absorbance of complementary colour
Distilled water to set absorbance at 0
Plot calibration curve
Measure absorbance of unknown concentration
Use graph to determine unknown concentration

Question 16

Vanadium oxidation states, ion formulae and colours

Answer 16

V(2+) purple +2
V(3+) green +3
VO(2+) blue +4
VO2 (+) yellow +5

Question 17

If exposed to air what happens to V(2+)

Answer 17

Oxidises to V(3+)

Question 18

Precise colours of vanadium solutions depends on

Answer 18

Acids used

Question 19

Catalyst definition

Answer 19

Substance that increases rate of chemical reaction

Without being used up

Question 20

How does catalyst work?

Answer 20

Provide alternative reaction pathway with lower activation energy

Question 21

How do variable oxidation states allow TM to act as catalysts?

Answer 21

Transition metal provides alternative route for reaction to take place by first changing oxidation state then changing back to original oxidation state

Question 22

How can you increase surface area of catalyst?

Answer 22

Grind into powder

Convert solid into mesh

Question 23

Examples of catalyst poisoning

Answer 23

Sulfur poisoning in Haber process

Lead poisoning in catalytic converters

Question 24

Why does catalyst need to be Goldilocks?

Answer 24

If adsorption too strong, molecules can’t move around the active sites and product can’t be released from the active sites
If adsorption too weak, not many molecules will be adsorbed and surface concentration will be too low

Question 25

How is surface area of catalyst maximised in Haber?

Answer 25

Pea sized lumps used

Question 26

Contact process

Answer 26

2so2 +o2 reversible to 2so3

Question 27

Catalyst for contact process

Answer 27

V2O5

Question 28

Define autocatalysis

Answer 28

One of products of reaction acts as catalyst

Question 29

What happens to coordination number when water and ammonia are exchanged?

Answer 29

Stay same

Question 30

Cobalt (II) and ammonia

Answer 30

Pink solution to yellow-brown solution

Complete substitution of water ligands

Question 31

Copper (II) and XS ammonia

Answer 31

Incomplete substitution of only 4 water ligands

Blue solution to deep blue solution

Question 32

What happens to coordination number when substituting small ligands with large ones?

Answer 32

Changes (decreases)

Question 33

Cobalt (II) and HCl

Answer 33

Complete substitution

Pink solution to blue solution

Question 34

What kind of substitution do ethanedioate ions undergo?

Answer 34

Complete

Question 35

What kind of substituion do 1,2-diaminoethane ions undergo?

Answer 35

Complete with cobalt 2

And incomplete with copper 2 to still leave 2 water ligands attached

Question 36

Test for sulfate ions

Answer 36

Acidify with hydrochloric acid
Add barium chloride
White precipitate of barium sulphate seen