Unit 5- Transition metals Flashcards
1
Q
explain the reactions of Cr (III) when:
- Aqueous Sodium hydroxide is added
- excess sodium hydroxide
- aqeuous ammonia added
- excess ammonia
A
- Cr (III) is voilet in aqeuous solutions
- In sodium hydroxide - Blue-Violet with a precipitate of Cr(H2O)3(OH)3
- in excess sodium hydroxide - precipitate dissolves to form green solution containing [Cr(H20)(OH)4]-
- in ammonia - Blue violet precipirate of Cr(H2O)3(OH3)3
- in excess ammonia - precipitate dissolves to form a yellow solution of [Cr(NH3]6]3+
2
Q
explain the reactions of Mn(II) when:
- Aqueous Sodium hydroxide is added
- excess sodium hydroxide
- aqeuous ammonia added
- excess ammonia
A
- In solution - very pale pink
- In sodium hydroxide - gelatinous white precipitate of Mn(OH)2 -turns brown on standing in air
- in excess sodium hydroxide - insoluble in excess
- In ammonia - gelatinous white precipirate of Mn(OH)2
- in excess ammonia - insolube in excess
3
Q
explain the reactions of Fe(II) when:
- Aqueous Sodium hydroxide is added
- excess sodium hydroxide
- aqeuous ammonia added
- excess ammonia
A
- Pale blue green in solution
- when sodium hydroxide is added - gelatinous pale green precipitate of Fe(OH)2- turns brown standing in air
- in excess sodium hydroxide- insoluble in excess
- when ammonia is added- gelatinous pale green precipitate of Fe(OH)2- turns brown standing in air
- in excess ammonia- insoluble in excess
4
Q
explain the reactions of FeIII) when:
- Aqueous Sodium hydroxide is added
- excess sodium hydroxide
- aqeuous ammonia added
- excess ammonia
A
- yellow in solution
- when sodium hydroxide is added- Reddish-brown precipitate of Fe(H2O)3(OH)3
- in excess sodium hydroxide- insoluble in excess
- when ammonia is added - reddish brown precipitate of Fe(H2O)3(OH)3
- excess ammonia - insoluble in excess
5
Q
explain the reactions of Ni(II) when:
- Aqueous Sodium hydroxide is added
- excess sodium hydroxide
- aqeuous ammonia added
- excess ammonia
A
- emerald green in solution
- when sodium hydoxide is added- emerald green precipirate of Ni(OH)2
- excess sodium hydroxide- insoluble in excess
- when ammonia is added- emerald green precipitate of Ni(OH)2
- excess ammonia - precipirate dissolves to form lavender blue solution of [Ni(NH)3]2+
6
Q
explain the reactions of Cu(II) when:
- Aqueous Sodium hydroxide is added
- excess sodium hydroxide
- aqeuous ammonia added
- excess ammonia
A
- blue in solution
- when sodium hydroxide is added- gelatinous blue precipirate of Cu(OH)2
- excess sodium hydroxide- insoluble in excess
- when ammonia is added- gelatinous blue preicipiate of Cu(OH)2
- excess ammonia- precipitate dissolves to form deep blue solution containing [Cu(NH)4(H2O)2]2+
7
Q
What are transition metals and how is this different to a d block element?
A
Transition metals are an element which forms one or more stable ions which have incompletely filled d sub-shells
d block elements are elements in the d block of the periodic table therefore between the s and p block
8
Q
What are the characteristics of transition metals?
A
- variable oxidition state ( generally +2 due to the lost of the outer 4s electrons)
- forms coloured ions in solution
- forms complex ions such as poly, mono and bidentate ligands
- acts as a catalyst
9
Q
what shapes are formed in complex ions?
A
- Planar - co-ordination number of 2
- tetrahedal- co-ordination number of 4 and complete d orbitals
- square planar- co-ordination number of 4 and incomplete d orbitals
- octahedral- co-ordination number of 6
10
Q
How do transition metals act as catalysts?
A
- reacting mixtures are adsorbed to the surface of the catalst.
- the larger the surface area, more reactants are adsorbed.
- Therefore the bonds between the reactants are weakened therefore less energy is needed to break the reacting molecules, lowering activation energy.
- adsorbed at specific points- active sites
- transition metals are normally heterogenous
- variable oxidation states also provide an alternative route with lower activation energy
11
Q
Describe the uses of some transition metals
A
- Iron is a structural material and a catalst
- copper is an electrical conductor
- copper (I) chloride is used in photochromic sunglasses. - mixed with silver chloride. in sunlight, equilibrium shfits to the right causing more silver atoms thus darkending the glass. ( Cu+ + Ag+ <=> Ag++ Cu2+)
- chemotherapy- cis-platin is used ( platinum compound) however trans-platin is more currently used due to less side effects. Gold is becoming more common in chemo also. works best with heat.
12
Q
Why is the development of new catalyst important?
A
- to reduce the environmental impact of industrial processes.
- reactions will take place at lower temperatures and pressures therefore less electricity therefore less carbon dioxide
- ethanoic acid from methanol reaction - used cobalt and iodide, 300 degrees and 700atm however now rhodium/idodide ion catalyst followed by iridium as it is less active. Iridium reduces cost, realeases less carbon dioxide, reduces the drying colums (less water used) and less by products therefore greater atom economy
13
Q
what are the oxidation states and colours of vanadium?
A
V2+ - Vanadium (II) - +2 -purple solution
V3+- Vanadium (III) - +3 - green solution
VO2+ - Oxovanadium (IV) - +4 - blue solution
VO2+ - Dioxovanadium (V) - +5 - yellow
14
Q
how to prepare Chromium(II) ethanoate
A
- sodium dichromate is reduced by hyrogen to producde Cr (II)
- tap funnel is opened and HCl runs in the flask where it reacts with Zinc to produce Hydrogen
- Hydrogenr reduces orange dichromate to green chromium(III) then to blue chromium(II).
- tap funnel is closed and hydrogen pressure builds up
- reactrs with sodium ehanoate
- red precipirate of Cr(II) ethanoate is produced.
- tube should be removed, sealed and cooled in running water
