Qualitative analysis

Question 1

[Cu(H20)6]2+ NH3 (dropwise) → Cu(OH)2

Answer 1

Pale blue (Cu2+) → Blue (precipitate)

Question 2

[Cu(H20)6]2+ NH3 (excess) → [Cu(NH3)4(H20)2]2+

Answer 2

Pale blue (Cu2+) → Dark blue

Question 3

[Cu(H20)6]2+ + 4Cl- ⇌ [CuCl4]2-

Answer 3

Pale blue (Cu2+) ⇌ Green (mix) ⇌ Yellow

Question 4

KCr(SO4)• 12(H2O) + H2O → [Cr(H20)6]3+

Answer 4

Colourless → Violet

Question 5

Cr2(SO4)3 + H2O → [Cr(H20)5SO4]+

Answer 5

Colourless → Green

Question 6

[Cr(H20)6]3+ + NH3 (dropwise) → Cr(OH)3

Answer 6

Violet → Grey-Green (precipitate)

Question 7

[Cr(H20)6]3+ + NH3 (excess) → [Cr(NH3)6]3+

Answer 7

Violet → Purple

Question 8

Cu2+ + 2OH- → Cu(OH)2

Answer 8

Pale Blue → Blue (Precipitate)

Question 9

Fe2+ + 2OH- → Fe(OH)2

Answer 9

Pale green → Green (precipitate)

Question 10

(in air) Fe(OH)2 → Fe(OH)3

Answer 10

Green (precipitate) → Orange-Brown (precipitate)

Question 11

Fe3+ + 3OH- → Fe(OH)3

Answer 11

Pale yellow → Orange-Brown (precipitate)

Question 12

Mn2+ + 2OH- → Mn(OH)2

Answer 12

Pale Pink → Light Brown (precipitate)

Question 13

Cr3+ + 3OH- → Cr(OH)3

Answer 13

Violet → Grey-Green (precipitate)

Question 14

Cr(OH)3 + 3OH- → [Cr(OH)6]3-

Answer 14

Grey-Green (precipitate) → Dark Green

Question 15

2Fe3+ 2I- → 2Fe2+ + I2

Answer 15

Orange-Brown (Fe3+) → Pale Green (Fe2+) + Brown (I2) so unclear

Question 16

MnO4- + 8H+ + 5Fe2+ → Mn2+ + 5fe3+ + 4H2O

Answer 16

Purple (Mn7+) → Colourless (Mn2+)

Question 17

Cr2O72- + 14H+ + 3Zn → 2Cr3+ + 7H2O + 3Zn2+

Answer 17

Orange (Cr6+) → Green (Cr3+)

Question 18

? + 2Cr3+ + 10OH- → 2CrO42- + 8H2O

Answer 18

Hot alkaline H2O2

Question 19

2Cu2+ + 4I- → 2CuI + I2

Answer 19

Pale blue (Cu2+) → White precipitate (CuI) + Brown (I2)

Question 20

Cu2O + H2SO4 → Cu + CuSO4 + H2O

Answer 20

Colourless → Brown (Cu precipitate) + Pale blue (Cu2+)

Question 21

NH4+ + OH- → NH3 + H2O

Answer 21

(damp litmus paper) Red → Blue

Question 22

CO32- + 2H+ → CO2 + H2O

Answer 22

effervescence (Lime water goes cloudy)

Question 23

SO4- + Ba2+ → BaSO4

Answer 23

White precipitate

Question 24

Cl- + Ag+ → AgCl

Answer 24

White precipitate, Soluble in dilute NH3

Question 25

Br- + Ag+ → AgBr

Answer 25

Cream precipitate, Soluble in Conc NH3

Question 26

I- + Ag+ → AgI

Answer 26

Yellow precipitate, Insoluble in Conc NH3

Question 27

I2 (at RTP, solution in water, solution in cyclohexane)

Answer 27

shiny grey-black solid, brown, violet

Question 28

Br2 (at RTP, solution in water, solution in cyclohexane)

Answer 28

red-brown liquid, orange, orange

Question 29

Cl2 (at RTP, solution in water, solution in cyclohexane)

Answer 29

pale green gas, pale green, pale green

Question 30

Sequence of anion tests and why

Answer 30

1. Carbonate test (Only CO32- will produce CO2) 2. Sulphate test (Ba2+ + CO32- would also produce white precipitate) 3. Halide test (all Ag compounds could form precipitate so important to remove/rule out the others first)