15.4 variable oxidation state

Question 1

how could transition metals have variable oxidation states?

Answer 1

similiar energy in both 3d & 4s sub-shells
- ions containing partially filled sub-shells of d e- could be easily lost / gained

Question 2

what is the main oxidation state for Mn -> Zn?

Answer 2

2+

Question 3

what is the main oxidation state for Sc -> Cr?

Answer 3

3+

Question 4

VO2 +

Answer 4

yellow (+5)

Question 5

VO 2+

Answer 5

blue (+4)

Question 6

V 3+

Answer 6

green (+3)

Question 7

V 2+

Answer 7

violet (+2)

Question 8

which is the strongest oxidising agent within vanadium oxidation states?

Answer 8

VO2 +

Question 9

where could VO 2+ be found in?

Answer 9

• exist as VO3- ion in NH4VO3

Question 10

Cr 3+

Answer 10

green

Question 11

Cr 2+

Answer 11

blue

Question 12

what are the reactants and conditions needed for reducing dichromate ions to Cr 2+ / Cr 3+?

Answer 12

zinc in acidic conditions: O2 in air will oxidise Cr2+ to Cr3+

Question 13

how could transition metals with low oxidative states be oxidised more easily?

Answer 13

in alkaline conditions

Question 14

how could dichromate ions be produced from Cr3+ ions?

Answer 14

use hydrogen peroxide & Cr3+ in alkaline conditions ( Cr[OH]6)3- )
followed by acidification

Question 15

list the 3 equations used to produce dichromate ions from Cr3+ ions.

Answer 15

1- H2O2 + 2e- -> 2 OH-
2- [Cr(OH)6]3- + 2 OH- -> CrO4 2- + 4H2O + 3e-

acidification: 2 CrO4 2- + 2H+ <-> Cr2O7 2- + H2O