5.3.1: Transition elements and 5.3.2: Qualitative analysis Flashcards
Define a transition element
A d block element that forms at least one stable ion with partially filled d subshell
Where are the transition metals located in the
periodic table?
In the middle block from Ti to Cu
What are the 2 elements in d block that are not
considered as transition metals?
Scandium and zinc
Why is scandium and zinc not considered as
transition metals?
Scandium only forms Sc3+, where the d orbitals are empty
Zinc only forms Zn2+ where the d orbitals are full
What is the noble gas configuration of chromium?
[Ar]4s1 3d5
What is the noble gas configuration of copper?
[Ar]4s1 3d10
Which electrons do transition metals lose first when
forming ions?
4s
What are some characteristic physical properties of
transition metals?
● Metallic ● High density ● High melting and boiling point ● Shiny ● Good conductors of heat and electricity
What are the characteristic chemical properties of transition metals (4 marks)?
● Variable oxidation states → take part in many redox reactions
● Coloured compounds/ions in solution
● Good catalysts
● Form complex ions
In potassium manganate (VII), what is the oxidation
number of Mn?
Mn = +7
What are the 2 main ways in which transition metals act
as an effective catalyst?
● They provide a surface on which reaction can take place
● They change oxidation states to form
intermediates required for pathways with lower
activation energy
Give some examples of transition metal catalysts and the
processes/reactions they catalyse (4 marks)?
● Iron - Haber process ● Vanadium (V) oxide - contact process ● Nickel - hydrogenation of alkenes ● Manganese (IV) oxide - decomposition of hydrogen peroxide ● Copper sulfate - hydrogen production
What is a complex ion?
Transition metal ion bonded to one or more ligands by coordinate bonds
Define a ligand
Molecule or an ion that can donate a pair of electrons to the metal to form a coordinate bond
What is a coordinate bond?
A bond in which one of the atom provides both the electrons required for bonding, also known as dative bonding.
What does the coordination number indicate?
The number of coordinate bonds formed
between the metal ion and its ligands
What is a mono/unidentate ligand?
A ligand that forms one co-ordinate bond to the central metal ion (one lone pair to donate)
What is a bidentate ligand?
A ligand that forms two coordinate bonds
to the central metal ion (2 lone pairs to
donate)
What is a multidentate ligand?
A ligand that forms three or more
coordinate bonds to the central metal ion
Give some examples of common monodentate
ligands (4 marks).
Cl-, H2O, NH3, CN
Name the most common bidentate ligand
ethane-1,2-diamine
ethanedioate; how many coordinate bonds can
it form to a transition metal ion?
2 co-ordinate bonds
benzene-1,2-diol; how many coordinate bonds
can it form to a transition metal ion?
2 coordinate bonds
ethane-1,2-diamine. What is its shortened
name? How many coordinate bonds does it form?
2 coordinate bonds, shortened name = en
How many coordinate bonds does EDTA4- form?
six
EDTA is a chelating agent, what does that mean?
EDTA decreases the concentration of
metal ions in the solution by binding to
them and forming complex ions
What ion is usually formed when a transition metal compound is dissolved in water? What shape is it?
Aqua ion, 6 H2O ligands around the central metal ion. Octahedral complex ion is formed
If a transition metal ion has 2 ligands, what shape is
it usually?
Linear
If a transition metal ion has 4 ligands, what shape is
it usually?
Tetrahedral
Name an exception to the general rule that ions with
4 ligands is generally tetrahedral. What shape is it?
Platin is square planar → forms cisplatin
What shape is a complex ion if it has 6 ligands?
Octahedral
How can complex ions display E-Z or cis-trans
isomerism? What shapes of ions does this apply to?
Ligands differ in the way in which they are arranged in space
2 ligands of the same type can be on the same side of the metal ion (next to each other), which forms the E or cis isomer
2 ligands of the same type can be on opposite sides of the metal ion (not next to each other), which forms the Z or trans isomer
Applies to square planar and octahedral complex ions
What conditions are needed for a complex ion to
display optical isomerism?
Usually applies to octahedral molecules with 2 or more bidentate ligands, so that the mirror images are non-superimposable
What is cis-platin used for? Describe its mechanism
of action
It is used as an anti-cancer drug
It binds to DNA of fast growing cancer cells and prevents cell division, hence reducing the growth of cancer
Which metal ion is present in a haem group?
Fe2+
What is the coordination number of a haem group?
6
What are the ligands in haem group?
4 nitrogen forming the porphyrin ring
1 oxygen
1 globin
Why is CO toxic?
CO also coordinately bonds to the Fe2+,and bonds more strongly to Fe2+ than O2.
Stops O2 from bonding to haemoglobin, so O2 cannot be transported around the body
What colour is [Cu(H2O)6]2+ solution?
pale blue
What colour is [Cu(NH3)4(H2O)2]2+ solution?
deep blue
What colour is [CuCl4]2- solution?
yellow
What colour is [Cr(H2O)6]3+ solution?
dark green
What is a precipitation reaction?
A reaction where soluble ions in separate solutions are mixed to form an insoluble compound
What colour is Fe2+’s aqua ion?
green
What colour is Fe3+’s aqua ion?
pale brown
What colour is Cr3+’s aqua ion?
violet
What colour is Mn2+’s aqua ion?
pink
When Cu2+ reacts with NH3 or OH-, what colour is the precipitate?
blue
When Fe2+ reacts with NH3 or OH-, what colour is the
precipitate?
green
When Mn2+ reacts with NH3 or OH-, what colour is the precipitate?
brown
When Cr3+ reacts with NH3 or OH-, what colour is the
precipitate?
green
When Fe3+ reacts with NH3 or OH-, what colour is the
precipitate?
brown
What colour is MnO4-?
purple
Write a half equation for the reduction of MnO4- to
Mn2+
MnO4- + 8H+ + 5e- → Mn2+ + 4H2O
Why are redox titrations with transition metal
compounds said to be self-indicating?
They usually involve a colour change as
the metal is changing oxidation state;
sometimes an indicator is still
needed/useful
What colour is Cr2O72-?
orange
What colour is Cr3+?
green
Write a half equation for the reduction of Cr2O72- to Cr3+.
CrO72- + 14H+ + 6e- → 2Cr3+ + 7H2O
Describe how to test for metal ions
● 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
Write the method used to test for ammonium ions
● Fill half the test tube with sample
● Add sodium hydroxide and warm gently
● Smelly gas is produced; damp red litmus paper turns blue
Why does lime water turn milky in the presence of
carbon dioxide?
When carbon dioxide is bubbled in calcium hydroxide (lime water), calcium carbonate precipitate is formed
