transition metal ions reactions

Question 1

State the equation and colour change when some OH- (aq) is added dropwise to the aqueous solution of Cu2+

Answer 1

• [Cu(H2O)6]2+(aq) + 2OH-(aq) -> [Cu(OH)2(H2O)4] (s) + 2H2O (l)
• pale blue solution to pale blue precipitate

Question 2

State the equation and colour change when some NH3 (aq) is added dropwise to the aqueous solution of Cu2+

Answer 2

[Cu(H2O)6]2+(aq) + 2NH3(aq) -> [Cu(OH)2(H2O)4] (s) + 2NH4+ (aq)

blue solution to pale blue ppt

Question 3

State the equation and colour change when some OH- (aq) is added dropwise to the aqueous solution of Fe2+

Answer 3

[Fe(H2O)6]2+ (aq) + 2OH- (aq) -> [Fe(OH)2(H2O)4] (s) + 2H2O (l)

pale green solution to dark green precipitate

Question 4

State the equation and colour change when some NH3 (aq) is added dropwise to the aqueous solution of Fe2+

Answer 4

[Fe(H2O)6]2+ (aq) + 2NH3 (aq) -> [Fe(OH)2(H2O)4] (s) + 2NH4+ (aq)

pale green solution to dark green precipate

Question 5

State the equation and colour change when some OH- (aq) is added dropwise to the aqueous solution of Fe3+

Answer 5

[Fe(H2O)6]3+ (aq) + 3OH- (aq) -> [Fe(OH)3(H2O)3] (s) + 3H2O (l)

yellow solution to orange/brown precipitate

Question 6

State the equation and colour change when some NH3 (aq) is added dropwise to the aqueous solution of Fe3+

Answer 6

[Fe(H2O)6]3+ (aq) + 3NH3 (aq) -> [Fe(OH)3(H2O)3] (s) + 3NH4+ (aq)

yellow solution to orange/brown precipitate

Question 7

State the equation and colour change when some OH- (aq) is added dropwise to the aqueous solution of Mn2+

Answer 7

[Mn(H2O)6]2+ (aq) + 2OH-(aq) -> [Mn(Oh)2(H2O)4] (s) + 2H2O (l)

a pale pink solution to pale brown precipitate

Question 8

State the equation and colour change when some NH3 (aq) is added dropwise to the aqueous solution of Mn2+

Answer 8

[Mn(H2O)6]2+ (aq) + 2NH3-(aq) -> [Mn(Oh)2(H2O)4] (s) + 2NH4+ (aq)

a pale pink solution to pale brown precipitate

Question 9

State the equation and colour change when some OH- (aq) is added dropwise to the aqueous solution of Cr3+

Answer 9

[Cr(H2O)6]3+ (aq) + 3OH-(aq) -> [Cr(OH)3(H2O)3] (s) + 3H2O (l)

pale purple (if heated turns green) solution to dark green precipitate

Question 10

State the equation and colour change when some NH3 (aq) is added dropwise to the aqueous solution of Cr3+

Answer 10

[Cr(H2O)6]3+ (aq) + 3NH3(aq) -> [Cr(OH)3(H2O)3] (s) + 3NH4+ (aq)

pale purple (if heated turns green) solution to dark green precipitate

Question 11

State the equation (if any) when excess OH- is added to the precipitate of copper (II) hydroxide

Answer 11

insoluble in excess NaOH so there is no change

stays as [Cu(OH)2(H2O)4] (s) a pale blue precipate

Question 12

State the equation (if any) when excess NH3 (aq) is added to the precipitate of copper (II) hydroxide

Answer 12

[Cu(OH)2(H2O)4] (s) forms [Cu(NH3)4(H2O)2]2+ (aq)

colour change from pale blue ppt to dark blue solution

Question 13

State the equation (if any) when excess OH- is added to the precipitate of iron (II) hydroxide

Answer 13

insoluble in excess NaOH so there is no change

stays as [Fe(OH)2(H2O)4] (s) dark green ppt

Question 14

State the equation (if any) when excess OH- is added to the precipitate of iron (II) hydroxide

Answer 14

insoluble in excess NH3 so there is no change

stays as [Fe(OH)2(H2O)4] (s) dark green ppt

Question 15

State the equation (if any) when excess OH- is added to the precipitate of iron (III) hydroxide

Answer 15

insoluble in excess NaOH so there is no change

stays as [Fe(OH)3(H2O)3] (s) orange/brown ppt

Question 16

State the equation (if any) when excess NH3 is added to the precipitate of iron (III) hydroxide

Answer 16

insoluble in excess NH3 so there is no change

stays as [Fe(OH)3(H2O)3] (s) orange/brown ppt

Question 17

State the equation (if any) when excess OH- is added to the precipitate of manganese (II) hydroxide

Answer 17

insoluble in excess NaOH no change

stays as [Mn(Oh)2(H2O)4] (s) pale brown ppt

Question 18

State the equation (if any) when excess NH3 is added to the precipitate of manganese (II) hydroxide

Answer 18

insoluble in excess NH3 no change

stays as [Mn(Oh)2(H2O)4] (s) pale brown ppt

Question 19

State the equation (if any) when excess OH- is added to the precipitate of chromium (III) hydroxide

Answer 19

[Cr(OH)3(H2O)3] (s) forms Cr(OH)6 3- (aq)

tuns from dark green ppt to dark green solution

Question 20

State the equation (if any) when excess NH3 is added to the precipitate of chromium (III) hydroxide

Answer 20

[Cr(OH)3(H2O)3] (s) forms Cr(NH3)6 3+ (aq)

turns from dark green ppt to purple solution

Question 21

MnO4-/Fe2+ –> Mn2+/Fe3+

Answer 21

• purple (MnO4-) to pale pink (Mn2+)
• in titrations it is so dilute that it is practically colourless

Question 22

I-/Fe3+ –> I2/Fe2+

Answer 22

orange brown (Fe3+) to brown (I2)

Question 23

name the 5 transition metal ions and their colours in solution

Answer 23

Cr 3+ = green
-
Fe 2+ = pale green
-
Fe 3+ = yellow
-
Mn 2+ = pale pink

Question 24

what is the pattern for ionic equations of transition metal reactions with OH- ions? use M as for the metal and x for the charge

Answer 24

M X+ + xOH- -> M(OH)x

Question 25

what are the colours of the 5 transition metal hydroxide precipitates?

Answer 25

Cu(OH)2 = blue - Cr(OH)3 = grey/green - Fe(OH)2 = green - Fe(OH)3 = orange/brown - Mn(OH)2 = light brown

Question 26

which metal hydroxides change colour on standing with air? give reason why

Answer 26

- Fe(OH)2 turns from green to orange/brown at the surface as Fe2+ oxidises to Fe3+ - Mn(OH)2 darkens on standing with air

Question 27

what reagents are used to reduce Fe3+ to Fe2+? what is the colour change

Answer 27

- iodide ions I- - yellow to pale green

Question 28

what happens if Cl- ions are added to Cu2+ solution? give full complex equation

Answer 28

- ligand substitution - colour change from blue to yellow [Cu(H2O)6]2+ + 4Cl- -> [CuCl4]2- + 6H2O

Question 29

what reagents are used to oxidise Cr3+ to Cr2O7 2-? what is the colour change

Answer 29

- warm hydrogen peroxide H2O2/OH- - green to orange

Question 30

what reagents are used to reduce Cu2+ to Cu+? what is the color change?

Answer 30

- iodide ions I- - blue solution to off-white precipitate of CuI

Question 31

what happens to Cu+ in solution?

Answer 31

spontaneously disproportionates into Cu2+ and Cu(s)

Question 32

what happens to Cu+ in the solution?

Answer 32

spontaneously disproportionates into Cu2+ and Cu(s)

Question 33

list the hydroxide precipitates that react with excess aqueous ammonia

Answer 33

1. Cr III 2. Cu II

Question 34

list the hydroxide precipitates that react with excess NaOH

Answer 34

1. Cr III