Redox/titration metals

Question 1

Oxidising Fe 2+ to Fe 3+

Answer 1

MnO4/ H+ - (to Mn 2+)
purple to colourless

Question 2

Reducing Fe 3+ to Fe 2+

Answer 2

Iodide (2I -) to Iodine(I2)
colour change of Fe masked by I2 formed

Question 3

Reducing (Cr6+) in Cr2O7 2- to Cr 3+

Answer 3

Zn/H+
Orange to green (Cr)
(excess zinc Cr 3+ to Cr 2+ (pale blue))

Question 4

oxidising Cr 3+ to Cr 6+ (in Cr2O7 2-)

Answer 4

Hot alkaline hydrogen peroxide

Question 5

Cu 2+ reduced to Cu +

Answer 5

reaction with Iodide ions (4I -)
Formation of brown iodine and CuI white precipitate

Question 6

Cu + oxidised to Cu 2+

Answer 6

disproportionation reaction of hot dilute sulphuric acid
Cu2O +H2SO4 —> Cu +CuSO4 +H2O

Question 7

Cu 2+ precipitation reaction eg. with NaOH

Answer 7

Pale blue solution to pale blue precipitate

Question 8

Cu 2+ ligand substitution with 4NH3

Answer 8

pale blue solution to dark blue solution (PARTIAL LIGAND SUB)

Question 9

Cu 2+ ligand substitution with 4Cl- (could use conc HCl)

Answer 9

pale blue solution to yellow solution
(shape change from octahedral to tetrahedral as Cl- ligand bigger)

[Cu(H2O)6] 2+ +4Cl - —-> [CuCl4] 2- +6H2O

Question 10

Cr 3+ precipitation reaction with eg. NaOH

Answer 10

Violet solution to grey/green precip

Question 11

Cr 3+ ligand substitution with 6NH3

Answer 11

Violet solution to purple solution

Question 12

Cr(OH)3 reacts further with NaOH

Answer 12

grey green precipitate to dark green solution [Cr(OH)6] 3-

Question 13

Mn 2+ precipitation reaction

Answer 13

pale pink solution to light brown precipitate

Question 14

Fe 2+ precipitation reaction

Answer 14

Pale green solution to green precipitate

Question 15

Fe 3+ precipitation reaction

Answer 15

pale yellow solution to orange/brown precipitate