5.3.1- Transition Elements & 5.3.2- Qualitative Analysis

Question 1

Define a transition element

Answer 1

A d block element that forms at least one stable ion with partially filled d subshell

Question 2

Where are transition metals located in periodic table?

Answer 2

In middle block from Ti to Cu

Question 3

What are the 2 elements in d block that are not considered as transition metals?

Answer 3

Scandium and Zinc

Question 4

Why are scandium and zinc not considered as transition metals?

Answer 4

Scandium only forms Sc^3+, where the d orbitals are empty
Zinc only forms Zn^2+ where d orbitals are full

Question 5

What is the noble gas configuration of chronium?

Answer 5

[Ar]4s1 3d5

Question 6

What is noble gas configuration of copper?

Answer 6

[Ar]4s1 3d10

Question 7

Which electrons do transition metals lose first when forming ions?

Answer 7

4s

Question 8

What are some characteristic physical properties of transition metals?

Answer 8

• Metallic
• High density
• High melting and boiling point
• Shiny
• Good conductors of heat and electricity

Question 9

What are characteristic chemical properties of transition metals?

Answer 9

• Variable oxidation states -> take part in many redox reactions
• Coloured compounds/ ions in solution
• Good catalysts
• Form complex ions

Question 10

In potassium manganate(VII) what is oxidation number of Mn?

Answer 10

Mn= +7

Question 11

What are 2 main ways in which transition metals act as an effective catalyst

Answer 11

• They provide a surface on which reactions can take place
• They change oxidation states to form intermediates required for pathways with lower activation energy

Question 12

Give some examples of transition metals located catalysts and the reactions they catalyse (5)?

Answer 12

• Iron- haber process
• Vanadium (V) oxide- contact process
• Nickel- hydrogenation of alkenes
• Manganese (IV) oxide- decomposition of hydrogen peroxide
• Copper sulfate- hydrogen production

Question 13

What is a compex ion?

Answer 13

Transition metal ion bonded to one or more ligands by coordinate bonds

Question 15

What is a coordinate bond?

Answer 15

A bond in which one of the atom provides both the electrons required for bonding, also known as dative bonding

Question 16

Define a ligand

Answer 16

Molecule or an ion that can donate a pair of electrons to the metal to form a coordinate bond

Question 16

What does coordinate number indicate?

Answer 16

The number of coordinate bonds formed between the metal ion and its ligand

Question 17

What is a mono/ unidentate ligand?

Answer 17

A ligand that forms one coordinate bond to the central metal ion (one lone pair to donate)

Question 18

What is a bidentate ligand?

Answer 18

A ligand that forms two coordinate bonds to the central metal ion (2 lone pairs to donate)

Question 19

What is a multidentate ligand?

Answer 19

A ligand that forms three or more coordinate bonds to the central metal ion

Question 20

Give some examples of common monodentate ligands (4)

Answer 20

Cl-
H2O
NH3
CN-

Question 21

Name the most common bidentate ligand

Answer 21

ethane-1,2- diamine

Question 22

How many coordinate bonds does EDTA^4- form?

Answer 22

Six

Question 23

EDTA is a chelating agent, what does that mean?

Answer 23

EDTA decreases the concentration of metal ions in solution by binding to them and forming complex ions

Question 24

What ion is usually formed when a transition metal compound is dissolved in water? What shape is it?

Answer 24

Aqua ion. 6H2O ligands around central metal ion. Octahedral complex is formed.

Question 25

If a transition metal has 2 ligands, what shape is it usually?

Answer 25

Linear

Question 26

If a transition metal has 4 ligands, what shape is it usually?

Answer 26

Tetrahedral

Question 27

Name an exception to the general rule that ions with 4 ligands is generally tetrahedral. What shape is it?

Answer 27

Platin is square planar -> forms cisplatin

Question 28

What shape is a complex ion if it has 6 ligands?

Answer 28

Octahedral

Question 29

How can compex ions display E-Z or cis-trans isomerism? What shapes of ions does this apply to?

Answer 29

Ligands differ in the way in which they are arranged in space. 2 ligands of same type can be on the same side of the metal ions (next to each other), which forms E or cis isomer 2 ligands of the same type can be on opposite sides of the metal ion (next to each other), which forms the Z or trans isomer Applies to square planar or octahedral complex ions

Question 30

What conditions are needed for a complex ion to display optical isomerism?

Answer 30

Usually applies to octahedral molecules, with 2 or more bidentate ligands so that the mirror images are non-superimposable

Question 31

What is cis-platin used for? Describe its mechanism of action?

Answer 31

- It is used as an anti-cancer drug - It binds to DNA of fast growing cancer cells and prevents cell division, hence reducing growth of cancer

Question 32

Which metal ion is present in a haem group?

Answer 32

Fe2+

Question 33

What is the coordination number of a haem group?

Answer 33

6

Question 34

What are the ligands in haem group?

Answer 34

- 4 nitrogen forming the porphyrin ring - 1 oxygen - 1 globin

Question 35

Why is CO toxic?

Answer 35

CO also coordinately bonds to the Fe2+ and bonds more strongly than O2. Stops O2 from bonding to haemoglobin so O2 cannot be transported around the body

Question 36

What colour is [Cu(H2O06]2+ solution?

Answer 36

Pale blue

Question 37

What colour is [Cu(NH3)4(H2O)2]2+ solution?

Answer 37

Deep blue

Question 38

What colour is [CuCl4]2- solution?

Answer 38

Yellow

Question 39

What colour is [Cr(H2O)6]3+ solution?

Answer 39

Dark green

Question 40

What is a precipitation reaction?

Answer 40

A reaction where soluble ions in separate solutions are mixed to form an insoluble compound

Question 41

What colour is Fe2+'s aqua ion?

Answer 41

Green

Question 42

What colour is Fe3+'s aqua ion?

Answer 42

Pale brown

Question 43

What colour is Cr3+'s aqua ion?

Answer 43

Violet

Question 44

What colour is Mn2+'s aqua ion?

Answer 44

Pink

Question 45

When Cu2+ reacts with NH3 or OH-, what colour is the precipitate?

Answer 45

Blue

Question 46

When Fe2+ reacts with NH3 or OH-, what colour is the precipitate?

Answer 46

Green

Question 47

When Mn2+ reacts with NH3 or OH-, what colour is precipitate ion?

Answer 47

Brown

Question 48

When Cr3+ reacts with NH3 or OH-, what colour is the precipitate?

Answer 48

Green

Question 49

When Fe3+ reacts with NH3 or OH-, what colour is the precipitate?

Answer 49

Brown

Question 50

What colour is MnO4-?

Answer 50

Purple

Question 51

Write a half equation for the reduction of MnO4- to Mn2+

Answer 51

MnO4- + 8H+ + 5e- -> Mn2+ + 4H2O

Question 52

Why are redox titrations with transition metal compounds said to be self-indicating?

Answer 52

They usually involve a colour change as the metal is changing oxidation state; sometimes an indicator is still needed/ useful

Question 53

What colour is Cr2O7^2-?

Answer 53

Orange

Question 54

What colour is Cr3+?

Answer 54

Green

Question 55

Write a half equation for the reduction of Cr2O7^2- to Cr3+

Answer 55

Cr2O7^2- + 14H+ + 6e- -> 2Cr3+ + 7H2O

Question 56

Describe how to test for metal ions

Answer 56

- Fill half of the test tube with the sample - Add aqueous ammonia or sodium hydroxide drop by drop - Colour of precipitate indicates the ion present

Question 57

Write the method used to test for ammonium ions

Answer 57

- Fill half the test tube with sample - Add sodium hydroxide and warm gently - Smelly gas is produced; damp red litmus paper turns blue

Question 58

Why does lime water turn milky in the presence of carbon dioxide?

Answer 58

When carbon dioxide is bubbled in calcium hydroxide (lime water), calcium carbonate precipitate is formed