Transition elements Module 5

Question 1

Where are the transition elements found?

Answer 1

In the d block

Question 2

Definition of a transistion element?

Answer 2

A d block element, that can form at least one stable ion with an incomplete d sub shell

So scandium and Zinc aren’t transition elements

Question 3

Which transition elements are exceptions to the electron configuration filling up rules?

Answer 3

Chromium- prefers to have one electron in each orbital of the 3d subshell and just one in the 4s subshell, makes it more stable

Copper- prefers to have a full 3d subshell, and only one electron in the 4s subshell

Question 4

When transition elements form ions, what shell are the electrons lost from first?

Answer 4

4s

Question 5

Why scandium and Zinc aren’t transition elements?

Answer 5

Zn2+ only ion, which has a full d subshell

Sc3+ only ion, doesn’t have a d subshell

Question 6

What is special about oxidation numbers in transition elements?

Answer 6

They can exist in variable oxidation states

Question 7

Why are transistion elements good catalysts?

Answer 7

They can change oxidation states by losing or gaining electrons, within their d orbitals, so can transfer electrons to speed up reactions

Good at adsorbing substances onto their surfaces to lower the activation energy of reactions

Question 8

3 examples of transition elements acting as catalysts?

Answer 8

CuSO4 catalyses the reaction of zinc with acids

MnO4 catalyses the decomposition of hydrogen peroxide

Iron is the catalyst in the haber process to produce ammonia

Question 9

Pros and cons of catalysts?

Answer 9

Good for industry and the environment, as they allow reactions to happen faster, and at lower temperatures and pressures reducing energy usage

Can pose health risks as many of the metals and their compounds are toxic

Question 10

Formula for when a transition element, is in aqueous solution?

Answer 10

{M(H2O)6)n+

Question 11

What happens when you mix Copper(II) with NH3 (including equations)?

Answer 11

Cu2(+) + 2OH- = Cu(OH)2 goes from pale blue solution to a pale blue precipitate
OH is there as NH3 is a weak alkali

Then in excess NH3,Cu(OH)2 dissolves to form {Cu(NH3)4(H2O)2}2+ which is a dark blue colour

So the reaction is 4NH3 + {Cu(H20)6}2+ = (reversible) {Cu(NH3)4(H20)2}(2+) + 4H2O

Question 12

What happens when you mix Iron(II) with NH3 (including equations)?

Answer 12

Fe(2+) + 2OH- = Fe(OH)2 pale green solution to a green precipitate, OH there as NH3 is a weak alkali

Question 13

What happens when you mix Iron(III) with NH3 (including equations)?

Answer 13

Fe3+ + 3OH- = Fe(OH)3 goes from yellow solution to an orange precipitate, OH there as NH3 is a weak acid

Question 14

What happens when you mix Manganese (II) with NH3 (including equations)?

Answer 14

Mn(2+) + 2OH- = Mn(OH)2 goes from pale pink solution to a light brown precipitate

Question 15

What happens when you mix Chromium (III) with NH3 (including equations)?

Answer 15

Cr(3+) + 3OH- = Cr(OH)3 goes from a purple solution to a grey-green precipitate

Then in excess NH3, Cr(OH)3 dissolves to form {Cr(NH3)6}(3 +)which is a purple solution

So the equation is {Cr(H2O)6} + 6NH3 =(reversible) {Cr(NH3)6}(3+) + 6H20

Question 16

What’s a complex ion?

Answer 16

A metal ion surrounded by coordinately (dative bond, both electrons are from the same atom) bonded ligands

Question 17

What’s a ligand?

Answer 17

An atom, ion or molecule, that donates a pair of electrons to a central metal atom or ion

Question 18

What’s the coordination number?

Answer 18

The number of coordinate bonds that are formed with the central metal atom (will either be 4 or 6)

Question 19

What shape does 6 coordinate bonds form?

Answer 19

An octahedral shape, 90 degree bond angle

Question 20

What shape does 4 coordinate bonds form?

Answer 20

Tetrahedral shape, 109.5 degree bond angle, or a square planar shape 90 degree bond angle

Question 21

What must all ligands have?

Answer 21

A lone pair of electrons to be able to form the coordinate bond

1 lone pair = monodentate
2 lone pairs = bidentate, so can form 2 coordinate bonds with central atom

Question 22

When can optical ismomerism occur in complex ions?

Answer 22

Occurs when an ion can exist in 2 non-superimposable mirror images (don’t match each other when put on top of each other)

So occurs when in octahedral complexes, when 3 biodentate ligands are attached to the central ion

Question 23

How can cis-trans isomerism occur in complex ions?

Answer 23

When there’s only 2 different groups involved

The Cis isomers have the same groups on the same side (so are close together as they can be)

Trans have the same groups on opposite side

Question 24

What is Cis platin?

Answer 24

A complex of platinum(II), with 2 chloride ions and 2 ammonia molecules in a square planar shape

Question 25

How does Cis-Platin act as an anti cancer drug?

Answer 25

The 2 chloride ligands are very easy to displace. So the cis-platin displaces them, and bonds to 2 Nitrogen atoms on the DNA molecule, inside the cancerous cell instead This block on it's DNA prevents the cancerous cell from reproducing by division, causing the cell to die as unable to repair the damage

Question 26

Why does Cis-platin need to be CIs and not Trans?

Answer 26

Needs the 2 chloride ions to be next to each other, in order to bind and work correctly

Question 27

Downside of Cis-Platin as a cancer treatment?

Answer 27

Prevents normal cells from reproducing, including blood, so represses the immune system, increasing risk of infection Can also damage the kidneys

Question 28

In ligand subsitution what happens if the ligands are of similar size, eg H20, NH3 or CN-?

Answer 28

The ligands directly swap places, and the coordination number stays the same (sometimes may be partial)

Question 29

In ligand subsitution what happens if the ligands are of different sizes, eg H2O and Cl-?

Answer 29

There's a change of coordination number and shape

Question 30

How do you write a ligand substiution reaction?

Answer 30

Complex ion and reactant ligand on one side Reversible reaction sign New complex ion (coordination number, shape and charge may have changed) and the displaced ligand

Question 31

Describe the Ligand substiution in haemoglobin?

Answer 31

Haemoglobin contains Fe2+ ions, which form 6 coordinate bonds, 4 of the lone pairs come from Nitrogen atoms, within a circular part of the molecule called haem, the fifth lone pair comes from a nitrogen atom binded to a protein (globin) The last one is a water ligand which attaches to the Iron In the lungs there is high oxygen concentration, so the water ligand is substituted for an Oxygen molecule, forming oxyhaemoglbobin, this is then transported to respiring tissues where the oxygen is now dropped off and O2 concentration is low, so H2O binds back on Can explain this reffering to le Chateillers principles and the reversible equation

Question 32

What happens if CO is inhaled?

Answer 32

Water ligand is swapped for CO, forming a carboxyhaemoglobin, it's a strong ligand so won't readily exchange back with oxygen or water lingands, meaning haemoglobin can't transport oxygen anymore

Question 33

How do transition elements change oxidation number?

Answer 33

By gaining or losing electrons during a redox reaction

Question 34

Describe the interconversion between Fe 2+ ions and Fe3+ ions?

Answer 34

Fe(2+) ions (pale green) are oxidised to Fe(3+) (yellow), by acidified potassium manganate solution Fe(3+) ions (yellow) are reduced to Fe(2+) ions (pale green) by Iodide ions

Question 35

Interconversion between Cr(3+) and Cr2O7(2-)?

Answer 35

Cr(3+) ion in (Cr(OH)6)3- (dark green) is oxidised to the yellow CrO4(2-) by warming with hydrogen peroxide solution in alkaline conditions Then dilute sulfuric acid is added to CrO4(2-) to produce the orange Cr2O7(2-) Cr2O7(2-) (orange) is reduced to Cr3+ (green) by acidified zinc

Question 36

Interconversion between Cu2+ and Cu+?

Answer 36

Cu(2+) (pale blue) is reduced to the off-white precipitate Copper iodide by iodide ions Cu(+) spontaneously disproportionates into to produce Cu and Cu(2+)

Question 37

What colour precipitate is formed, when NaOH is reacted with the transistion Ion Cu(2+)?

Answer 37

blue

Question 38

What colour precipitate is formed, when NaOH is reacted with the transistion Ion Fe(2+)?

Answer 38

green

Question 39

What colour precipitate is formed, when NaOH is reacted with the transistion Ion Fe(3+)?

Answer 39

Orange

Question 40

What colour precipitate is formed, when NaOH is reacted with the transistion Ion Mn(2+)?

Answer 40

Light brown

Question 41

What colour precipitate is formed, when NaOH is reacted with the transistion Ion Cr(3+)?

Answer 41

Grey/green

Question 42

How do you test for a carbonate ligand?

Answer 42

Add Nitric acid to the test compound, and bubble any gas given off through limewater Limewater will go cloudy if present, as CO2 produced

Question 43

How do you test for a chloride ligand?

Answer 43

Add silver nitrate to the compound White precipitate formed if present

Question 44

How do you test for a bromide ligand?

Answer 44

Add silver nitrate to the compound Cream precipitate forms if present

Question 45

How do you test for an Iodide ligand?

Answer 45

Add silver nitrate to the compound Yellow precipitate forms if present

Question 46

How do you test for Sulphate ligand?

Answer 46

Add Barium Nitrate or Barium Chloride, white precipitate will form if present

Question 47

How do you test for an ammonium ligand?

Answer 47

Add cold NaOH to the test compound and warm, hold damp, red litmus paper over the solution Red litmus paper will turn blue in presence of ammonia

Question 48

How do you get [Cr(OH)6]?

Answer 48

React Cr(OH)3 with NaOH

Question 49

How do you get {Cu(Cl)4}2-?

Answer 49

{Cu(H2O)6}(2+) + 4Cl- =(reversible) {Cu(Cl)4}(2-) + 6H2O