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CHEMISTRY OCR A > 5.7 TRANSITION ELEMENTS > Flashcards

5.7 TRANSITION ELEMENTS Flashcards

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1
Q

What are D-block elements?

A

D-block elements:
- located between group 2 and group 13
- 3rd subshell has the highest energy
- electrons added to 3d orbitals
- all metallic (high mp and bp, shiny, conduct electricity and heat)
- used in coinage, construction, production of tools, electrical cables, water pipes, aerospace industry, medical applications (joint replacement and cosmetic dentistry)

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2
Q

What are the anomalies for electron configuration of d-block elements?

A

Chromium and copper do not follow the expected principle for electron configuration. This is due to stability, a half filled d5 subshell and a fully filled d10 subshell give additional stability to atoms of Cr and Cu

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3
Q

What is the configuration of ions for d block elements?

A

Configuration of ions:
- lose 4s electrons before any others
- this means that when forming an atom, the 4s orbital fills before the 3d orbitals but when forming an ion the 4s empties before the 3d

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4
Q

What are transition elements?

A

Transition elements are d block elements that form at least one ion with a partially filled d orbital
- although scandium and zinc are d block elements they do not match the definition and are not transition elements
- scandium only forms Sc3+ by losing two 4s electrons and one 3d electron (removing the 3d orbital)
- zinc only forms Zn2+ by the loss of two 4s electrons (leaving a full 3d orbital)

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5
Q

What are the properties of transition metals and compounds?

A

Properties:
- form compounds in which the transition element has different oxidation states
- they form coloured compounds
- the elements and their compounds can act as catalysts

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6
Q

Variable oxidation states.

A

Variable oxidation states:
- transition elements form compounds with more than one oxidation state
- e.g iron forms two chlorides FeCl2 and FeCl3
- the number of oxidation states increase across the transition elements to manganese, then decreases
- all transition elements form compounds with an oxidation number of +2, resulting from the loss of two electrons
- each oxidation state often has a characteristic colour
- a species containing a transition element in its highest oxidation state is often a strong oxidising agent

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7
Q

Formation of coloured compounds.

A

Formation of coloured compounds:
- compounds and ions of transition elements are frequently coloured
- potassium dichromate (VI) is bright orange, cobalt (II) chloride is pink-purple, nickel (II) sulfate is green, whilst hydrated copper (II) sulfate is blue
- the solid compounds can be dissolved in water to produced coloured solutions
- the colour of a solution is linked to the partially filled d-orbitals of the transition metal ion
- the colour of a solution can vary with different oxidation states
= e.g iron (II) is pale green, iron (III) is yellow
= e.g chromium (III) is green and chromium (VI) is yellow or orange

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8
Q

Transition metals as catalysts.

A

Transition metals as catalysts:
- important catalysts used in a variety of industrial processes and in the lab
= the haber process is catalysed by a finely divided iron catalyst
= contact process is catalysed by vanadium (V) oxide V2O5
= hydrogenation of vegetable fats in the manufacture of margarine uses a nickel catalyst
= catalytic decomposition of hydrogen peroxide forming oxygen uses manganese (IV) oxide MnO2
- heterogenous catalysts ^
- homogenous catalysts
= reaction between iodide ions and peroxodisulfate ions S2O8-
= the reaction of zinc with acids is catalysed by the presence of Cu2+

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9
Q

What are complex ions?

A

Complex ions:
- metal ions form complex ions by accepting electron pairs from other ions or molecules
- the bonds formed are dative covalent bonds (coordinate bonds)
- an ion or molecule (with a lone pair of electrons) that can form such bonds with a transition metal are known as ligands
- all complex ions have a metal ion centre of ligands surrounding it (usually 4-6)
- the coordination number refers to the number of dative covalent bonds

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10
Q

What are monodentate ligands?

A

Monodentate ligands form one dative covalent bond with metal ion
Cl- OH - CN- NH3 H20

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11
Q

What are bidentate ligands?

A

Bidentate ligands form two dative covalent bonds with metal ion
H2NCH2CH2NH2 C2O4^2-

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12
Q

What is stereoisomerism (cis trans) in complex ions?

A

Stereoisomerism:
- square planar complexes or the form [MA2B2]^n exist in two forms
- at least one pair of identical ligands at 180 = trans
- at least one pair of identical ligands at 90 = cis

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13
Q

How is optical isomerism shown in complex ions?

A

Optical isomerism:
- octahedral complexes with bidentate ligands can exist as a pair of enatiomers (optical isomers)

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14
Q

What are the properties of ligands?

A

Properties of ligands:
- some ions/molecules like H2O do not make particularly good ligands and can be replaced by better ligands
- NH3 is a better ligand due to nitrogen being less electronegative than oxygen
- Cl- is a better ligand as it is negatively charged, making it electrostatically attracted to the positive transition metal ion

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15
Q

What is cis-platin?

A

Cis-platin:
- used in medicine as an anti-cancer drug
- works by forming a platinum complex inside of a cell which binds to DNA and prevents the DNA of the cell from replication (targets tumour cells)
- use can lead to kidney damage

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16
Q

What colour is Ti3+?

A

Ti3+ is purple/lilac.

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17
Q

What colour is V2+?

A

V2+ is purple/lilac.

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18
Q

What colour is V3+?

A

V3+ is green.

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19
Q

What colour is V4+?

A

V4+ is blue.

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20
Q

What colour is V5+?

A

V5+ is yellow.

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21
Q

What colour is Cr2+?

A

Cr2+ is blue.

22
Q

What colour is Cr3+?

A

Cr3+ is green.

23
Q

What colour is Cr6+?

A

Cr6+ is orange.

24
Q

What colour is Mn2+?

A

Mn2+ is pink.

25
Q

What colour is Mn4+?

A

Mn4+ is brick red.

26
Q

What colour is Mn6+?

A

Mn6+ is green.

27
Q

What colour is Mn7+?

A

Mn7+ is purple/lilac.

28
Q

What colour is Fe2+?

A

Fe2+ is pale green.

29
Q

What colour is Fe3+?

A

Fe3+ is pale yellow/brown.

30
Q

What colour is Co2+?

A

Co2+ is pink.

31
Q

What colour is Co3+?

A

Co3+ is green.

32
Q

What colour is Ni2+?

A

Ni2+ is green.

33
Q

What colour is Cu2+?

A

Cu2+ is blue.

34
Q

What is the equation and what is formed when Cu2+ ions are mixed with NaOH?

A

When Cu2+ mixed with NaOH:
Cu2+ + 2OH- = Cu(OH)2
- blue solution reacts to form a blue precipitate of copper II hydroxide
- the precipitate is insoluble in excess NaOH

35
Q

What is the equation and what is formed when Fe2+ ions are mixed with NaOH?

A

When Fe2+ mixed with NaOH:
Fe2+ + 2OH- = Fe(OH)2
- pale green solution reacts to form a green precipitate of iron II hydroxide
- the precipitate is insoluble in excess NaOH but turns brown at its surface on standing in air as iron II is oxidised to iron II
Fe(OH)2 = Fe(OH)3

36
Q

What is the equation and what is formed when Fe3+ ions are mixed with NaOH?

A

When Fe3+ mixed with NaOH:
Fe3+ + 3OH- = Fe(OH)3
- pale yellow solution reacts to form an orange brown precipitate of iron III hydroxide
- the precipitate is insoluble in excess NaOH

37
Q

What is the equation and what is formed when Mn2+ ions are mixed with NaOH?

A

When Mn2+ mixed with NaOH:
Mn2+ +2OH- = Mn(OH)2
- pale pink solution reacts to form a light brown precipitate of manganese II hydroxide which darkens on standing in air
- the precipitate is insoluble in excess NaOH

38
Q

What is the equation and what is formed when Cr3+ ions are mixed with NaOH?

A

When Cr3+ mixed with NaOH:
Cr3+ + 3OH- = Cr(OH)3
- violet solution reacts to form a grey green precipitate of chromium III hydroxide
- the precipitate is soluble in excess NaOH forming a dark green solution
Cr(OH)3 + 3OH- = [Cr(OH)6]3-

39
Q

What is the precipitation reaction when Cu(OH)2 is mixed with excess NH3?

A

When Cu(OH)2 mixed with NH3:
Cu(OH)2 + 4NH3 = [Cu(NH3)4(H2O)2]3+
- blue precipitate dissolves in excess NH3 to form a deep blue solution containing [Cu(NH3)4(H2O)2]3+

40
Q

What is the precipitation reaction when Cr(OH)3 is mixed with excess NH3?

A

When Cr(OH)3 mixed with NH3:
Cr(OH)3 + 3NH3 = [Cr(NH3)6]3+
- green precipitate dissolves in excess NH3 to form a purple solution containing [Cr(NH3)6]3+

41
Q

What occurs when Fe2+, Fe3+ and Mn2+ are mixed with excess NH3?

A

When Fe2+, Fe3+ and Mn2+ are mixed with excess NH3, the precipitates do not dissolve and form Fe(OH)2, Fe(OH)3 and Mn(OH)2.

42
Q

What happens when carbonate ions are mixed with dilute nitric acid?

A

When carbonate ions mixed with HNO3:
CO3^2- + 2H+ = CO2 + H2O
- effervescence as carbon dioxide is evolved.

43
Q

What happens when sulfate ions are mixed with Barium ions?

A

When sulfate ions mixed with Ba2+
Ba2+ + SO4^2- = BaSO4
- white precipitate of BaSO4 formed.

44
Q

What happens when halide ions are mixed with silver ions?

A

When halides mixed with Ag+:
Cl- + Ag+ = AgCl
- white precipitate of AgCl formed
- precipitate soluble in dilute NH3
Br- + Ag+ = AgBr
- cream precipitate of AgBr formed
- precipitate soluble in concentrated NH3
I- + Ag+ = AgI
- yellow precipitate of AgI formed
- precipitate insoluble in NH3

45
Q

What is the equation and what is formed in the redox reactions involving Fe2+ and Fe3+?

A

Oxidation of Fe2+ to Fe3+:
MnO4^- + 8H+ + 5Fe2+ = Mn2+ + 5Fe3+ + 4H2O
- acidic conditions, used as a basis for a redox titration
- Fe2+ oxidised to Fe3+
- MnO4^- reduced to Mn2+
- purple solution decolourised by Fe2+ ions to form a colourless solution (purple to colourless)

Reduction of Fe3+ to Fe2+:
2Fe3+ + 2I- = 2Fe2+ + I2
- Fe3+ reduced to Fe2+
- I- oxidised to I2
- orange-brown solution reduced to pale green, however colour change is obscured by the oxidation of I- (no colour change)

46
Q

What is the equation and what is formed in the redox reaction involving Cr2O7^2- and Cr3+?

A

Reduction of Cr2O7^2- to Cr3+:
Cr2O7^2- + 14H+ + 3Zn = 2Cr3+ + 7H2O + 3Zn2+
- acidified Cr2O7^2- and addition of Zn as zinc is most powerful oxidising agent
- orange solution to green
- with an excess of zinc, chromium III ions are reduced further to chromium II ions
Zn + Cr3+ = Zn2+ + Cr2+
- green solution to pale blue

47
Q

What is the equation and what is formed in the redox reaction involving Cr3+ and CrO4^2-?

A

Oxidation of Cr3+ to CrO4^2-:
3H2O2 + 2Cr3+ + 10OH- = 2CrO4^2- + 8H2O
- chromium is oxidised from +3 in Cr3+ to +6 in CrO4^2-
- oxygen is reduced from -1 in H2O2 to -2 in CrO4^2-
- hot alkaline H2O2 used (powerful oxidising agent) used to oxidise chromium III to chromium IV

48
Q

What is the equation and what is formed in the redox reaction involving Cu2+ and Cu+?

A

Reduction of Cu2+ to Cu+:
2Cu2+ + 4I- = 2CuI + I2
- I- oxidised to I2
- Cu2+ reduced to Cu+
- pale solution forms white precipitate of CuI

49
Q

What is the disproportionation reaction involving Cu+ ions?

A

Disproportionation of Cu2+:
Cu2O + H2SO4 = Cu + CuSO4 + H2O
- Cu2O mixed with hot dilute H2SO4
- forms brown solid of Cu and a blue solution of CuSO4
- Cu+ ions simultaneously oxidised and reduced
- oxidised from +1 in Cu2O to 0 in Cu
- reduced from +1 in Cu2O to +2 in CuSO4

50
Q

What is the reaction of ammonium ions to form ammonia?

A

Ammonium to form ammonia:
NH4^+ + OH- = NH3 + H2O
- heated
- to test for ammonium ion, NaOH is heated gently with solution analysed
- if ammonia is evolved damp red pH indicator paper will turn blue, indicating presence of ammonium ions.

CHEMISTRY OCR A (28 decks)

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