m5 - transition metals

Question 1

why are d block elements called d block

Answer 1

d is their outer (highest energy) sub shell

Question 2

transition metal def

Answer 2

a d-block element that forms at least one stable ion with an incomplete d-subshell

Question 3

electron configuration of transition metals

Answer 3

fill 4s2 shell first before 3d
EXCEPT in Cr and Cu

Cr ends in 3d5 4s1
Cu ends in 3d10 4s1

Question 4

how many unpaired electrons does Cr have

Answer 4

6

Question 5

which 2 are not transition elements

Answer 5

Sc and Zn
Sc only forms a 3+ ion in which the d subshell is empty
Zn forms only a 2+ ion in which the d subshell is full
so they don’t form any ions with a partially filled d subshell therefore not transition

Question 6

transition metals being used as catalysts (2 examples)

Answer 6

iron in haber process
mno2 in decomposition of h2o2

Question 7

what is a complex ion

Answer 7

a transition metal ion surrounded by (6) ligands

Question 8

ligand def

Answer 8

molecule or ion with a lone pair of e- that’s able to form a dative (coordinate bond) to the central metal ion by donation of this e- pair

Question 9

monodentate ligand examples and def

Answer 9

form one coordinate bond

h2o
nh3
cl-

Question 10

bidentate ligands example and def

Answer 10

form 2 coordinate bonds

nh2ch2ch2nh2

Question 11

coordination number def

Answer 11

no of coordinate bonds between central metal ion and it’s ligands

Question 12

if there are 6 coordination bonds what shape is the molecule

Answer 12

octahedral

Question 13

4 coordination bonds around a central atom is what shape

Answer 13

tetrahedral or square planar

Question 14

stereoisomerism in complex ions, bond angle for cis is

Answer 14

90°

so (example Cl) are next to each other

Question 15

stereoisomerism in complex ions, bond angle for trans is

Answer 15

180°

so (example Cl) are opposite each other

Question 16

optical isomers hack

Answer 16

flip them so a mirror image

Question 17

ligand substitution reactions and colour -> copper dissolving in water
(there are 2 reactions, one with cl one with nh3)

Answer 17

when dissolved in water = [Cu(H2O)6] 2+ + Cl-
water ligands can then be replaced by other ligands eg chloride from conc acid -> [CuCl4] 2-
blue => yellow

or 4 ammonias

[Cu(H2O)6] 2+ + 4NH3 -><- [Cu(NH3)4(H2O)2] 2+ + 4H2O
blue => deep blue

Question 18

ligand substitution reaction and colour - chromium dissolving in water

Answer 18

forms [Cr(H2O)6] 3+ + NH3 -> Cr(OH)3 + excess NH3 -> [Cr(NH3)6] 3+
violet => purple

[Cr(H2O)6] 3+ + NaOH -> Cr(OH)3 + excess NaOH -> [Cr(OH)6] 3-
violet => green

Question 19

reduction of Cu2+ to Cu+ using iodine ions

Answer 19

2Cu2+ + 4I- —> 2CuI + I2

Question 20

inter conversion between Fe2+ and Fe3+ (oxidation and reduction)

Answer 20

pale green => yellow
oxidation reaction by something eg MnO4- or Cr2O7 2-

reduction reaction by something eg I- colourless —> red brown I2

Question 21

inter conversion between Cr3+ and Cr2O7 2-

Answer 21

oxidation: green => orange in acidic conditions by oxidising agent
or green => yellow in alkaline OH- by H2O2

reduction: orange => green in acidic conditions by reducing agents eg Zn

Question 22

biochemical importance of iron

Answer 22

haemoglobin has Fe2+ ion at centre (5 coordinate N ligands)
oxygen acts as a ligand and binds readily to it, carried to cells where it’s released (weak and reversible attraction)

oxygen ligands can be replaced by CO ligands which bind more strongly and irreversibly, reduces O2 around body, tissues starved of oxygen and die

Question 23

colour of Cr3+ metal-aqua ion

Answer 23

violet solution

[Cr(H2O)6]3+

Question 24

colour of Fe2+ metal aqua ion

Answer 24

green solution

[Fe(H2O)6]2+

Question 25

colour of Fe3+ metal aqua ion

Answer 25

yellow solution

Question 26

colour of Mn2+ metal aqua ion

Answer 26

pale pink solution

Question 27

colour of Cu2+ metal aqua ion

Answer 27

blue solution

Question 28

colour of Cr3+ with OH- (and then xs OH-)

Answer 28

green precipitate Cr(OH)3

xs: green solution [Cr(OH)6] 3-

Question 29

colour of Fe2+ with OH-

Answer 29

green precipitate Fe(OH)2

Question 30

colour of Fe3+ with OH-

Answer 30

brown precipitate Fe(OH)3

Question 31

colour of Mn2+ with OH-

Answer 31

pale brown precipitate Mn(OH)2

Question 32

colour of Cu2+ with OH-

Answer 32

blue precipitate Cu(OH)2

Question 33

colour of Cr3+ with xs NH3

Answer 33

purple solution

[Cr(NH3)6] 3+

Question 34

colour of Cu2+ with xs NH3

Answer 34

dark blue solution

[Cu(NH3)4(h2o)2] 2+