transition elements colours Flashcards
[Cu(H2O)6]2+ (aq)
pale blue solution
Cu(OH)2 (s)
- NH3 added drop wise to Cu2+ (aq)
- pale blue precipatate
[Cu(NH3)4(H2O)2]2+
- excess NH3 to Cu2+ (aq)
- dark blue
CuCl4 2-
- excess HCl to Cu2+ (aq)
- yellow solution
Cu+
- reduction of Cu2+ with I-
- white precipitate (CuI)
- brown solution (I2)
CoCl4 2-
- formed from CoCl2.6H2O + water and excess HCl
- blue solution
[Cr(H2O)6] 3+
- from KCr(SO4)2.12H2O (s)
- pale purple (with heat turns green)
- due to impurities it is common for Cr (III) to appear green in solution
Cr(OH)3 (s)
- NH3 dropwise to Cr3+ (aq)
- dark green precipitate
[Cr(NH3)6] 3+ (aq)
- excess NH3 to Cr2+
- purple solution
CrO4 2-
- oxidation of Cr3+ with hot alkaline H2O2
- yellow solution
[Mn(H2O)6]2+
- from MnSO4.4H2O (s)
- pale pink solution
Mn(OH)2 (s)
- NaOH dropwise to Mn2+
- pale brown precipitate
[Fe(H2O)6]2+
- from FeSO4.7H2O (s)
- pale green
Fe(OH)3 (s)
- NaOH dropwise to Fe3+ (aq)
- orange/brown precipitate
MnO4-/Fe2+ –> Mn2+/Fe3+
- purple (MnO4-) to pale pink (Mn2+)
- in titrations it is so dilute that it is practically colourless
I-/Fe3+ –> I2/Fe2+
orange brown (Fe3+) to brown (I2)
Cu2+/Cu
- brown solid (Cu)
- CuSO4 blue solution
[Cr(OH)6]3-
- excess OH- to Cr(OH)3
- dark green solution
Cr2O7 2-
- from K2Cr2O7 in 0.1mol H2SO4
- orange solution
Fe(OH)2
- NaOH dropwise to Fe2+
- dark green precipitate
[Fe(H2O)6]3+
- from FeCl3.6H2O
- yellow solution
name the 5 transition metal ions and their colours in solution
Cr 3+ = green
-
Fe 2+ = pale green
-
Fe 3+ = yellow
-
Mn 2+ = pale pink
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
M X+ + xOH- -> M(OH)x
what are the colours of the 5 transition metal hydroxide precipitates?
Cr(OH)3 = grey/green
-
Fe(OH)2 = green
-
Fe(OH)3 = orange/brown
-
Mn(OH)2 = light brown
which metal hydroxides change colour on standing with air? give reason why
- 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
What happens if excess NaOH is added to Cr(OH)3? give an equation
- Cr(OH)3 precipitate redissolved to form a dark green solution of [Cr(OH)6]3+
-
- Cr(OH)3 (s) + 3OH- (aq) -> [Cr(OH)6]3- (aq)
what happens if excess NH3 is added to Cu(OH)2? give full complex equation
- Cu(OH)2 precipitate redissolved to form a dark blue solution of [Cu(NH3)4(H2O)2]2+
- [Cu(H2O)6]2+ (aq) + 4NH3 (aq) -> [Cu(NH3)4(H2O)2]2+ (aq) + 4H2O (l)
what happens if excess NH3 is added to Cr(OH)3? give the full complex equation
- Cr(OH)3 precipitate redissolved to form purple solution of [Cr(NH3)6]3+
- [Cr(H2O)6]3+ (aq) + 6NH3 (aq) -> [Cr(NH3)6]3+ (aq) + 6H2O (l)
what happens if Cl- ions are added to Cu2+ solution? give full complex equation
- ligand substitution
- colour change from blue to yellow
[Cu(H2O)6]2+ + 4Cl- -> [CuCl4]2- + 6H2O
what reagents are used to reduce Fe3+ to Fe2+? what is the colour change
- iodide ions I-
- yellow to pale green
what reagents are used to oxidise Cr3+ to Cr2O7 2-? what is the colour change
- warm hydrogen peroxide H2O2/OH-
- green to orange
what reagents are used to reduce Cu2+ to Cu+? what is the color change?
- iodide ions I-
- blue solution to off-white precipitate of CuI
what happens to Cu+ in solution>
spontaneously disproportionates into Cu2+ and Cu(s)
