3.2.5 - Transition metals

Question 1

Why is the reaction slow before a catalyst is added? (2)

Answer 1

• Negative ions repel
• Resulting in high activation energy

Question 2

Why does s block not form catalysts?

Answer 2

They don’t have variable oxidation states

Question 3

What determines pH level? (3)

Answer 3

• Charge to size ratio
• Greater ratio = more polarising = weaker O-H bond
• More H+ ions released

Hexa-aqua ions can dissasociate to produce H+ ions

Question 4

Colours of iron2/3, copper, aluminium and their reaction products (except Cl- reaction)

Answer 4

Iron 2+ = Green
Iron 3+ = Brown
Copper = Blue
Aluminium = White

Question 5

What is a bidentate ligand?

Answer 5

A ligand which binds to a metal in 2 different places via donation of 2 lone pairs

Question 6

How are the coordinate bonds formed?

Answer 6

Ligand donates lone pair of electrons to central metal ion

Question 7

What is the only ligand that forms tetrahedral complexes?

Answer 7

Chlorine

Question 8

What shape does NH3 ligands form?

Answer 8

Octahedral

Question 9

What isomerism do bidentate ligands exhibit?

Answer 9

Optical isomerism

Question 10

What isomerism do square planar complexes exhibit?

Answer 10

Cis-trans

Question 11

What isomerism do octahedral complexes exhibit? How do you determine which isomer it is?

Answer 11

• Cis-trans
• If the two odd ligands are opposite each other, it is trans

Question 12

List all possible shapes of molecules and examples of each

Answer 12

• Octahedral (NH3/bidentates)
• Tetrahedral (chlorine)
• Square planar (cis-platin)
• Linear (silver)

Question 13

Why are complex ions coloured? (3)

Answer 13

• Absorption of certain wavelengths of light
• Causes promotion of d-orbital electrons
• Remaining wavelengths reflected

Question 14

Why might the enthalpy change of a reaction be very small/0? (2)

Answer 14

• Same types of bonds broken and made (i.e Cu—N)
• Same number of bonds broken and made

Question 15

Why may a reaction become feasible? (3)

Answer 15

• Increase in number of particles
• Increase in entropy
• Free energy change becomes negative

Question 16

Why is chlorine not a ligand?

Answer 16

It does not donate a lone pair

Question 17

How does the iron catalyst in the Haber process work? (3)

Answer 17

• Reactants bind to active site of catalyst (adsorption)
• Reaction takes place
• Products desorb from catalyst

Question 18

How can the iron catalyst become poisoned in the Haber process?

Answer 18

• Sulfur binds to catalyst
• Blocking active sites

Question 19

How would you use colorimetry to determine the concentration of a sample? (3)

Answer 19

• Produce calibration curve
• By testing known concentrations of the sample with the colorimeter
• Compare the sample against the curve

Question 20

What is the overall equation for the reaction between S2O8(2-) and I-?

Fe2+ is the catalyst for this reaction

Answer 20

S2O8(2-) + 2I- —–> I2 + 2SO4(2-)

Question 21

What are the two reactions to show Fe2+ is a catalyst?

Answer 21

1. S2O8(2-) + 2Fe(2+) —-> 2Fe(3+) + 2SO4(2-)
2. 2Fe(3+) + 2I- —-> I2 + 2Fe(2+)

Fe2+ lowers the Ea because oppositely charged ions attract

Question 22

What is the reaction between MnO4- and C2O4(2-)?

Mn2+ is the autocatalyst for this reaction, 2:5 ratio

Answer 22

2MnO4- + 16H+ + 5C2O4(2-) —-> 2Mn(2+) +8H2O + 10CO2

Question 23

What are the two equations which show that Mn2+ acts as a catalyst?

Answer 23

1. 4Mn2+ + MnO4- + 8H+ —-> 5Mn3+ + 4H2O
2. 2Mn3+ + C2O4(2-) —-> 2Mn(2+) + 2CO2

Mn2+ lowers Ea beacuse oppositely charged ions attract

Question 24

What is the equation of the reaction between Fe(2+) and MnO4-?

5:1 ratio

Answer 24

MnO4- + 8H+ + 5Fe(2+) —-> Mn(2+) + 4H2O + 5Fe(3+)

Question 25

What are the two Contact Process equations?

Answer 25

1. V2O5 + SO2 ----> V2O4 + SO3 2. V2O4 + 0.5O2 ----> V2O5