transition metals

Question 1

Where are d-block elements located and what are they?

Answer 1

d-block elements are elements with the highest energy electrons in the d-subshell and are located between group 2 and group 13 from scandium to zinc

Question 2

What is a transition element?

Answer 2

A transition element is a d-block element that forms at least one ion with a partially filled d-orbital.

Question 3

Why are scandium and zinc not considered d-block elements?

Answer 3

Scandium only forms one Sc3+ ion from the loss of two 4s electrons and one 3d electron so they have no partially filled d-orbital

Zinc only forms Zn2+ by the loss of two electrons leaving from the 4s subshell leaving 3d subshells completely filled and not partially filled.

Question 4

What are the main features of transition elements?

Answer 4

+ They can form compounds with different oxidation states with each oxidation state having a characteristic colour
+ They can form coloured compounds
+ The elements and compounds of transition elements can act as catalysts

Question 5

What is a complex ion?

Answer 5

A complex ion is formed when one or more molecules/negatively charged ions (ligands) bond to a central metal ion.

Question 6

What is a ligand?

Answer 6

A ligand is a molecule or ion which donates a pair of electrons to a central metal ion to form a dative/coordinate bond.

Question 7

What is the coordination number?

Answer 7

The coordination number is the number of coordinate bonds attached to the central metal ion.

Question 8

What are monodentate, bidentate and multidentate ligands? Provide some examples.

Answer 8

Monodentate ligands only donate one pair of electrons to the central metal ion, e.g NH3, H2O, CL-, CN-, OH-

Bidentate ligands donate two pairs of lone electrons to the central metal ion forming two covalent bonds, for example 1,2 diaminoethane which provides two NH2

Multidentate ligands form three or more coordinate bonds by donating atleast three electron pairs for example EDTA that can form 6 dative covalent bonds

Question 9

What does EDTA stand for?

Answer 9

Ethylenediaminetetraaceticacid

Question 10

What shape will a complex ion have with 6 coordinate bonds?

Answer 10

Octahedral shape with a bond angle of 90*

Question 11

What shape will a complex ion have with four coordinate bonds?

Answer 11

Either will have a tetrahedral shape with bond angle 109.5* or a square planar shape if the complex ion is formed with a metal with the eight d-electrons in the highest energy d-subshell e.g platnium (II)

Question 12

What type of isomerism is found in square planar complexes?

Answer 12

Have the simplest form of cis-trans isomerism where they have no more than 2 identical ligands attached to the central metal ion.

cis: same side
trans: opposite side

Question 13

What type of isomerism is found in octahedral complexes?

Answer 13

Octahedral complexes with four types of one type of ligand and two of another type of ligand can exist as cis-trans isomerism.

Octahedral complexes with bidentate ligands can also show cis-trans isomerism.
Octahedral complexes with two or more bidentate ligands can form optical isomers which are non-superimposable mirror images of each other

Question 14

What is ligand substitution?

Answer 14

A reversible reaction where one type of ligand in a complex ion is replaced by another ligand to become more stable or for equilibrium reasons.

Question 15

What happens when [Cu(H2O)6] 2+ reacts with excess ammonia via a ligand substitution reaction? What colour changes occur?

Answer 15

+Initially a blue precipitate intermediate of Cu(OH)2 will form but will dissolve in excess ammonia if added
+ In the final product, four H2O molecules will be replaced by four NH3 molecules to become [Cu(NH3)4(H2O)2]
+ The colour will shift from a pale blue solution to a dark blue
+ There is no change of coordination number or shape

Question 16

What happens when [Cu(H2O)6] 2+ reacts with excess HCL via a ligand substitution reaction? What colour changes occur?

Answer 16

+ 4CL- ions will displace all the water molecules in [Cu(H2O)6] 2+ as CL- ions are bigger than H2O molecules
+ The shape will change from an octahedral to a tetrahedral as less ions fit around the central atom
+ The colour will change from pale blue to yellow

Question 17

What happens when [Cr(H2O)6]3+ reacts with excess excess ammonia via a ligand substitution reaction? What colour changes occur?

Answer 17

+ The six water molecules will be replaced by six molecules of NH3
+ Colour will change from violet to purple
+ Before the final product an intermediate can form of Cr(OH)3 when adding ammonia dropwise which is grey green. The final product is produced in excess ammonia.
+ Product = [Cr(NH3)6]3+

Question 18

How do haemoglobin show an example of ligand substitution reactions?

Answer 18

Haemoglobin contains 4 protein chains which have a haem molecule which can bind to O2.
When binding to O2 will form oxyhemoglobin which can later release O2 to body cells.
Carbon monoxide can also bind to the Fe3+ on the haem groups to form carboxyhaemoglobin where the O2 is replaced by CO.
This is a very stable bond and therefore prevents the carrying of O2.

Question 19

What is the colour change that occurs when Cu2+ reacts with NaOH?

Answer 19

Froms a blue precipitate of Cu(OH)2 from a pale blue solution

Question 20

What is the colour change that occurs when Fe2+ reacts with NaOH?

Answer 20

Forms a green precipitate of Fe(OH)2 from a pale green solution

Question 21

What is the colour change that occurs when Fe3+ reacts with NaOH?

Answer 21

Forms a orange-brown precipitate with formulae Fe(OH)3 from a pale green solution

Question 22

What is the colour change that occurs when Mn2+ reacts with NaOH?

Answer 22

Forms a brown precipitate of Mn(OH)2 from a pale pink solution

Question 23

What is the colour change that occurs when Cr3+ reacts with NaOH?

Answer 23

Forms a green precipitate of Cr(OH)3 from a violet solution

Question 24

What transition metal ions will dissolve in excess ammonia?

Answer 24

Cu2+ and Cr3+

Question 25

What transition metal ions will dissolve in excess NaOH?

Answer 25

Cr3+ which will change from a violet solution to a green precipitate then a dark green solution

Question 26

How can Fe2+ be oxidised to Fe3+ and what colour changes occur?

Answer 26

Fe 2+ can be oxidised to Fe3+ via acidified potassium maganate ions , MnO4-
The colour will change from purple to colourless

MnO4- + 8H+ + 5Fe -> Mn2+ + 5Fe3+ + 4H2O

Question 27

How can Fe3+ be reduced to Fe2+ and what observations can be made?

Answer 27

Fe3+ can be reduced to Fe2+ with the use of iodide ions.
The colour will change from yellow-orange to pale green but the colour will be obscured by the production of iodine which is brown.

2Fe3+ + 2I- -> 2Fe2+ + I2

Question 28

How can Cr3+ be oxidised to chromate (VI) ions? (CrO42-) and what observations are made?

Answer 28

Oxidation occurs by hot alkaline hydrogen peroxide , H2O2

2Cr3+ + 3H2O + 10OH- -> 2CrO42- + 8H2O

Colour will change from green to yellow

Question 29

How can Cr2O7 2- ions be reduced to Cr3+ ions? state any observations!

Answer 29

Can be reduced by zinc metal.
Orange -> Green

Cr2O7 2- + 14H+ + 3Zn -> 2Cr3+ + 7H2O + 3Zn2+

Question 30

How can copper (II) ions be reduced Cu (I) ions?

Answer 30

Reduced to CuI by iodide ions
Forms a white precipitate from a pale blue solution

2Cu2+ + 4I- -> 2CuI + I2

Question 31

What disproportionation reaction does Cu2O go through?

Answer 31

Cu2O reacts with HOT dilute H2SO4 to form a brown precipitate of copper metal and a blue solution of copper (II) sulphate

Copper is reduced and oxidised at the same time

Cu2O + H2SO4 -> Cu + CuSO4 + H2O