Transitions Elements and Qualitative Analysis Flashcards
Define a transition element
A d-block element that forms at least one stable ion with partially filled d-sub shell
What are the 2 elements in d block that are not considered as transition metals?
Scandium and Zinc
Why are scandium and zinc not considered transition metals?
Scandium only forms Sc3+, where the d orbitals are empty.
Zinc only forms Zn2+ where the d orbitals are full
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)
- variable oxidation states —> take part in many redox reactions
- coloured compounds/ ions in solution
- good catalysts
- form complex ions
What are the two main ways in which transition metals act as an effective catalyst?
- they provide a surface on which reactions can take place
- they change oxidation states to form intermediates requires for pathways with lower activation energy
Give some examples of transition metal catalysts and the processes/reactions they catalyse? (5)
- 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 is a monodentate 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).
Cl-, H2O, NH3, CN-
Name the most common bidentate ligand.
ethane-1,2-diamine
How many coordinate bonds does EDTA4- form?
6
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.
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 are 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 Z or trans isomer.
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 cells and prevents cell division, hence reducing cell growth.
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 a 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+ that O2. Stops O2 from bonding to haemoglobin and being 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 metals 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 Cr2O7(2-)
Orange
What colour is Cr3+?
Green
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 CO2?
When carbon dioxide is bubbles in calcium hydroxide (lime water), calcium carbonate precipitate is formed.
