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Sams Chemistry > Transition Metals > Flashcards

Transition Metals Flashcards

1
Q

What is the formula of vanadium(V)Oxide ?

A

V2O5

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2
Q

Vanadium (V) Oxide is the catalyst used in the manufacture of sulfur trioxide. Give two equations to show how the catalyst is used and regenerated

A

V2O5 + SO2 —> SO3 + V2O4

V2O4 +1/2 O2 —> V2O5

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3
Q

A co-ordinate bond is formed when a transition metal ion reacts with a ligand.

Explain how this co-ordinate bond is formed.

A

An electron pair on the ligand

Is donated from the ligand to the central metal ion

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4
Q

Describe what you would observe when dilute aqueous ammonia is added dropwise, to excess, to an aqueous solution containing copper(II) ions.
Write equations for the reactions that occur.

A

Blue precipitate

Dissolves to give a dark blue solution

[Cu(H2O)6]2+ + 2NH3 –> Cu(H2O)4(OH)2 + 2NH4+

Cu(H2O)4(OH)2 + 4NH3 –> [Cu(NH3)4(H2O)2]2+ + 2OH– + 2H2O

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5
Q

When the complex ion [Cu(NH3)4(H2O)2]2+ reacts with 1,2-diaminoethane, the ammonia molecules but not the water molecules are replaced.
Write an equation for this reaction.

A

[Cu(NH3)4(H2O)2]2+ + 2H2NCH2CH2NH2 –>[Cu(H2NCH2CH2NH2)2(H2O)2]2+ + 4NH3

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6
Q

Suggest why the enthalpy change for the reaction in part (c) is approximately zero

A

Cu–N bonds formed have similar enthalpy / energy to Cu–N bonds broken

And the same number of bonds broken and made

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7
Q

Explain why the reaction in part (c) occurs despite having an enthalpy change that is approximately zero.

A

3 particles form 5 particles / disorder increases because more particles are formed / entropy change is positive

Therefore, the free-energy change is negative

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8
Q

Give the electron configuration of the Co atom and of the Co2+ ion.
State three characteristic features of the chemistry of cobalt and its compounds.

A

[Ar] 4s2 3d7 or 1s2 2s2 2p6 3s2 3p6 4s2 3d7

[Ar] 3d7 or 1s2 2s2 2p6 3s2 3p6 3d7

Any 3

Variable oxidation state

Act as catalysts

Form complexes

Form coloured ions/compounds

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9
Q

Ethane-1,2-diamine can act as a bidentate ligand. When [Co(H2O)6]2+(aq) ions are treated with an excess of ethane-1,2-diamine, the water ligands are replaced.

Explain what is meant by the term bidentate ligand.

Explain, with the aid of an equation, the thermodynamic reasons why this reaction occurs.

Draw a diagram to show the structure of the complex ion formed.

A

Two atoms that each donate a lone pair (of electrons) / coordinate bonds from two atoms

Formula of ethane-1,2- diamine: NH2CH2CH2NH2
M2 gained from equation or structure

[Co (H2O)6]2+ +3NH2CH2CH2NH2 → [Co(NH2CH2CH2NH2)3]2+ +6H2O

Equation must be balanced inc charges
Allow en or C2H8N2 in equation for ethane-1,2-diamine

There is an increase in the number of particles / the reaction goes from 4 moles to 7 moles
Allow increase number of molecules/moles. Allow numbers that match an incorrect equation

Disorder/entropy increases / ∆S is positive

∆G negative

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10
Q

In terms of electrons explain how the water molecules, not shown in the diagram, form bonds to the iron.

A

(lone) pair of electrons on oxygen/O

forms co-ordinate bond with Fe / donates electron pair to Fe

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11
Q

Predict the value of the bond angle between the two bonds to iron that are formed by these two water molecules

A

180°

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12
Q

Due to their electron arrangements, transition metals have characteristic properties including catalytic action and the formation of complexes with different shapes.

(a) Give two other characteristic properties of transition metals. For each property,illustrate your answer with a transition metal of your choice.

A

Variable oxidation state

eg Fe(II) and Fe (III)
Any correctly identified pair

(Characteristic) colour (of complexes)

eg Cu2+(aq) / [Cu(H2O)6]2+ is blue

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13
Q

Other than octahedral, there are several different shapes shown by transition metal complexes. Name three of these shapes and for each one give the formula of a complex with that shape.

A

Tetrahedral
[CuCl4]2– / [CoCl4]2–

Any correct complex

Square planar
(NH3)2PtCl2

Any correct complex

Linear
Do not allow linear planar
[Ag(NH3)2]+

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14
Q

Write an equation for the equilibrium that is established when hydrated calcium ions react with EDTA4– ions.

A

[Ca(H2O)6]2+ + EDTA4– –> [CaEDTA]2– + 6H2O

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15
Q

Explain why the equilibrium in part (c)
([Ca(H2O)6]2+ + EDTA4– –> [CaEDTA]2– + 6H2O) is displaced almost completely to the right to form the EDTA complex.

A

2 mol of reactants form 7 mol of products
Therefore disorder increases

Entropy increases / +ve entropy change / free-energy change is negative

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16
Q

Give the electron configuration of the Zn2+ ion.

Use your answer to explain why the Zn2+ ion is not classified as a transition metal ion

A

1s2 2s2 2p6 3s2 3p6 3d10

d sub-shell / shell / orbitals / sub-level full (or not partially full)

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17
Q

In terms of bonding, explain the meaning of the term complex

A

atom or ion or transition metal bonded to / surrounded by one or more ligands
by co–ordinate / dative (covalent) bonds / donation of
an electron pair

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18
Q

In terms of bonding, explain the meaning of the term complex

A

atom or ion or transition metal bonded to / surrounded by one or more ligands
by co–ordinate / dative (covalent) bonds / donation of
an electron pair

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19
Q

The element palladium is in the d block of the Periodic Table. Consider the following palladium compound which contains the sulfate ion.

[Pd(NH3)4]SO4

(i) Give the oxidation state of palladium in this compound.

A

+2 or 2+ or Pd2+ or II or +II or II+ or two or two plus

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20
Q

Give the names of two possible shapes for the complex palladium ion in this compound

A

square planar

tetrahedral

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21
Q

Transition metal ions can act as homogeneous catalysts in redox reactions. For example, iron(II) ions catalyse the reaction between peroxodisulfate (S2O82–) ions and iodide ions.

(a) State the meaning of the term homogeneous.

A

Same phase/state

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22
Q

Suggest why ions from s block elements do not usually act as catalysts.

A

Because only exist in one oxidation state

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23
Q

Write an equation for the overall reaction that occurs, in aqueous solution, between S2O82– ions and I– ions.

A

2I– + S2O82– → I2 + 2SO42–

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24
Q

Give one reason why, in the absence of a catalyst, the activation energy for the reaction between S2O82– ions and I– ions is high.

A

Both (ions)have a negative charge

Or (ions) repel each other

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25
Q

Write two equations to show how Fe2+ ions can catalyse the reaction between S2O82– ions and I– ions. Suggest one reason why the activation energy for each of these reactions is low.

Explain why Fe3+ ions are as effective as Fe2+ ions in catalysing this reaction.

A

2Fe2+ + S2O82– → 2Fe3+ + 2SO42–

2Fe3+ + 2I– → 2Fe2+ + I2

Equations 1 and 2 can occur in any order

26
Q

When cisplatin is absorbed into the human body, it undergoes a ligand substitution reaction and one chloride ligand is replaced by a water molecule forming a complex ion Q.

(a) Write an equation for this substitution reaction to form the complex ion Q.

A

Pt(NH3)2Cl2 + H2O → [Pt(NH3)2Cl(H2O)]+ + Cl–

27
Q

State and explain one risk associated with the use of cisplatin as an anticancer drug.

A

Killing them or causing damage (medical side effects)

May attach to DNA in normal cells

28
Q

state what is meant by ligand

A

An atom, ion or molecule which can donate a lone electron pair

29
Q

state what is meant by complex ion

A

A central metal ion/species surrounded by co-ordinately bonded ligands or ion in which co-ordination number exceeds oxidation state

30
Q

state what is meant by coordination number

A

The number of co-ordinate bonds formed to a central metal ion or number of electron pairs donated or donor atoms

31
Q

Iron forms many complexes that contain iron in oxidation states +2 and +3.
(a) Hexaaquairon(III) ions react with an excess of hydrochloric acid in a ligand substitution reaction.
Write an equation for this reaction.

A

[Fe(H2O)6]3+ + 4Cl− ⟶ FeCl4− + 6H2O

32
Q

Explain why the initial and final iron(III) complexes in the equation above have different shapes.
equation above:[Fe(H2O)6]3+ + 4Cl− ⟶ FeCl4− + 6H2O

A

Cl− is a bigger ligand

So only 4Cl− can fit around the metal

33
Q

The percentage of iron(II) sulfate in iron tablets can be determined by titration with potassium manganate(VII) in acidic solution.
Deduce an ionic equation for the reaction of iron(II) ions with manganate(VII) ions.

A

5Fe2+ + MnO4− + 8H+ ⟶ Mn2+ + 5Fe3+ + 4H2O

34
Q

Explain the meanings of the terms multidentate and ligand with reference to the reaction of EDTA4− with Cu(H2O)62+ ions to form a complex ion

A

Multidentate − EDTA can form many / six dative bonds with central cation.

Ligand − lone pair (on N or O of EDTA) can form dative bond with copper(II) ions.

35
Q

An incomplete method for recrystallisation of the nickel complex is outlined below.
Step 1: The sample is dissolved in a minimum volume of hot ethanol.
Step 2: The solution is filtered hot.
Step 3: The filtrate is cooled in ice to form crystals.
Explain the importance of each underlined point.
Minimum volume of hot ethanol _________________________________________
___________________________________________________________________
Filtered hot ______________

A

To form a saturated / highly-concentrated solution
So a saturated solution forms on cooling
1
To prevent crystals forming during filtration process

36
Q

A scientist was provided with a 5.0 g sample of a nickel-containing ore. The sample was ground into a powder and made into an aqueous solution. The solution was then added to an excess of dimethylglyoxime dissolved in ethanol. This was stirred until all of the ore had dissolved and all of the nickel ions had reacted to form a solid, red complex.
(a) Describe, with practical details, how an accurate value for the mass of the dimethylglyoxime-nickel complex could be obtained.
You should not include details of any calculations.

A

Filter the solution (under vacuum)
If filtration is not the first step max. 2/4
1
Wash with a (cold) solvent / water / ethanol
Steps must be in a logical sequence
1
Dry the solid by a suitable method
Dessicator / oven / leaving out on the side overnight / washing with propanone
1
Heat the dry product to constant mass to make sure it is dry

37
Q

The reaction between C2O42– ions and MnO4– ions is autocatalysed.
Explain what is meant by the term autocatalysed and identify the catalyst in the reaction.

A

A reaction that produces its own catalyst/ one of the products is the catalyst
1
Mn2+

38
Q

The reaction between C2O42– ions and MnO4– ions is very slow at first.
Explain why the reaction is initially slow.

A

There is no/very little catalyst at the start OR the reaction only speeds up when the catalyst is produced
1
Two negative ions (MnO4- and C2O42-) repel
Reference to molecules loses M2
1
The activation energy for the reaction is high / heat is required to overcome the activation energy

39
Q

Hexaaquairon(III) ions react with an excess of hydrochloric acid in a ligand substitution reaction.

Explain why the initial and final iron(III) complexes in the equation above have different shapes.

A

Cl− is a bigger ligand
1
So only 4Cl− can fit around the metal

40
Q

A co-ordinate bond is formed when a transition metal ion reacts with a ligand.
Explain how this co-ordinate bond is formed.

A

An electron pair on the ligand
1
Is donated from the ligand to the central metal ion

41
Q

Hexaaquairon(II) ions react with an excess of H2NCH2CH2NH2 in a ligand substitution reaction.
Which of the following shows the correct change in entropy for a reaction of hexaaquairon(II) ions with H2NCH2CH2NH2?
Tick (✔) one box.

change in entropy is negative

change in entropy is close to zero

change in entropy is positive

A

Change in entropy is positive

42
Q

Deduce an ionic equation for the reaction of iron(II) ions with manganate(VII) ions.

A

5Fe2+ + MnO4− + 8H+ ⟶ Mn2+ + 5Fe3+ + 4H2O

43
Q

Define Multidentate with reference to the reaction of EDTA4− with Cu(H2O)62+ ions to form a complex ion.

A

Multidentate − EDTA can form many / six dative bonds with central cation.

44
Q

Copper(II) compounds may be used as fungicides in vineyards. When used in this way, copper(II) ions can enter the water supply and cause problems because they are toxic in high concentrations.
The water supply near a vineyard can be tested for copper(II) ions by forming a blue aqueous complex with EDTA4− ions. The concentration of this complex can be determined using a colorimeter.
Outline the practical steps that you would follow, using colorimetry, to determine the concentration of this complex in a sample of water.

A

Calibrate a colorimeter / produce a calibration curve.
1
By testing the colorimeter with solutions of copper-EDTA complex of known concentration.
1
Add excess EDTA salt to the sample.

45
Q

Explain how the electron pair repulsion theory can be used to deduce the shape of, and the bond angle in, PF3

A

Stage 1: Electrons round P
• P has 5 electrons in the outside shell
• With 3 electrons from 3 fluorine, there are a total of 8 electrons in outside shell
• so 3 bond pairs, 1 non-bond pair
Stage 2: Electron pair repulsion theory
• Electron pairs repel as far as possible
• Lone pair repels more than bonding pairs
Stage 3: Conclusions
• Therefore, tetrahedral / trigonal pyramidal shape
• With angle of 109(.5)° decreased to 107°

46
Q

Suggest one reason why electron pair repulsion theory cannot be used to predict the shape of the [CoCl4]2− ion.

A

Too many electrons in d sub-shell / orbitals

47
Q

Predict the shape of, and the bond angle in, the complex rhodium ion [RhCl4]2−.

A

Tetrahedral (shape)

109.5°

48
Q

An acidified solution of NH4VO3 reacts with zinc.

Explain how observations from this reaction show that vanadium exists in at least two different oxidation states.

A

Explanation: Two different colours of solution are observed

Because each colour is due to vanadium in a different oxidation state

49
Q

A co-ordinate bond is formed when a transition metal ion reacts with a ligand.
Explain how this co-ordinate bond is formed.

A

An electron pair on the ligand

Is donated from the ligand to the central metal ion

50
Q

Describe what you would observe when dilute aqueous ammonia is added dropwise, to excess, to an aqueous solution containing copper(II) ions.
Write equations for the reactions that occur.

A

Blue precipitate
1
Dissolves to give a dark blue solution
1
[Cu(H2O)6]2+ + 2NH3 –>Cu(H2O)4(OH)2 + 2NH4+
1
Cu(H2O)4(OH)2 + 4NH3 –> [Cu(NH3)4(H2O)2]2+ + 2OH– + 2H2O

51
Q

When the complex ion [Cu(NH3)4(H2O)2]2+ reacts with 1,2-diaminoethane, the ammonia molecules but not the water molecules are replaced.
Write an equation for this reaction.

A

[Cu(NH3)4(H2O)2]2+ + 2H2NCH2CH2NH2 [Cu(H2NCH2CH2NH2)2(H2O)2]2+ + 4NH3

52
Q

When the complex ion [Cu(NH3)4(H2O)2]2+ reacts with 1,2-diaminoethane, the ammonia molecules but not the water molecules are replaced.

(d) Suggest why the enthalpy change for the reaction in part (c) is approximately zero.

A

Cu–N bonds formed have similar enthalpy / energy to Cu–N bonds broken

And the same number of bonds broken and made

53
Q

State what is meant by the term heterogeneous.

A

(The catalyst is in) a different state or phase (from the reactants)

54
Q

In the Contact Process sulfur dioxide reacts with oxygen to form sulfur trioxide as shown in the equation.
2SO2(g) + O2(g) ⇌ 2SO3(g)

Vanadium(V) oxide acts as a heterogeneous catalyst in the Contact Process.

Write two equations that show how this catalyst is involved in the Contact Process.

A

SO2 + V2O5 → SO3 + V2O4

V2O4 + 1/2 O2 –> V2O5

55
Q

Suggest why the vanadium(V) oxide is used in small pellet form rather than as large lumps

A

Surface area is increased

56
Q

State why the reactants should be purified before they come into contact with the vanadium(V) oxide catalyst

A

So that the catalyst is not poisoned

57
Q

Give the electron configuration of the Co atom and of the Co2+ ion.
State three characteristic features of the chemistry of cobalt and its compounds.

A

[Ar] 4s2 3d7 or 1s22s22p63s23p64s23d7
Allow 4s and 3d in either order

[Ar] 3d7 or 1s22s22p63s23p63d7

Any 3
Variable oxidation state
Act as catalysts
Form complexes
Form coloured ions/compounds
58
Q

Ethane-1,2-diamine can act as a bidentate ligand. When [Co(H2O)6]2+(aq) ions are treated with an excess of ethane-1,2-diamine, the water ligands are replaced.
Explain what is meant by the term bidentate ligand.
Explain, with the aid of an equation, the thermodynamic reasons why this reaction occurs.

A

Two atoms that each donate a lone pair (of electrons) / coordinate bonds from two atoms

Formula of ethane-1,2- diamine: NH2CH2CH2NH2
M2 gained from equation or structure

[Co (H2O)6]2+ +3NH2CH2CH2NH2 → [Co(NH2CH2CH2NH2)3]2+ +6H2O
Equation must be balanced inc charges
Allow en or C2H8N2 in equation for ethane-1,2-diamine

There is an increase in the number of particles / the reaction goes from 4 moles to 7 moles

Disorder/entropy increases / ∆S is positive

59
Q

The reaction between C2O42– ions and MnO4– ions is autocatalysed.
Explain what is meant by the term autocatalysed and identify the catalyst in the reaction.

A

A reaction that produces its own catalyst/ one of the products is the catalyst

Mn2+

60
Q

The reaction between C2O42– ions and MnO4– ions is very slow at first.
Explain why the reaction is initially slow.

A

There is no/very little catalyst at the start OR the reaction only speeds up when the catalyst is produced

Two negative ions (MnO4- and C2O42-) repel
Reference to molecules loses M2

The activation energy for the reaction is high / heat is required to overcome the activation energy

61
Q

A green solution, X, is thought to contain [Fe(H2O)6]2+ ions.
(a) The presence of these ions can be confirmed by reacting separate samples of solution X with aqueous ammonia and with aqueous sodium carbonate.
Write equations for each of these reactions and describe what you would observe.

A

[Fe(H2O)6]2+ + 2NH3 → Fe(H2O)4(OH)2 + 2NH4+
Allow equation with OH− provided equation showing formation of OH− from NH3 given

Green precipitate

[Fe(H2O)6]2+ + CO32− → FeCO3 + 6H2O

Green precipitate

62
Q

The redox reaction, in aqueous solution, between acidified potassium manganate(VII) and sodium ethanedioate is autocatalysed.
(a) Write an equation for this redox reaction.
Identify the species that acts as the catalyst.
Explain how the properties of the species enable it to act as a catalyst in this reaction.

A

2MnO4− + 16H+ + 5C2O42− → 2Mn2+ + 8H2O + 10CO2
1
Mn2+ OR Mn3+
If catalyst incorrect can only score M1 and M3
1
(Possible because) Mn can exist in variable oxidation states
1
Ea lowered because oppositely charged ions attract
These marks can be gained in any order
1
Mn3+ (reduced) to Mn2+ by C2O42− / equation
M5 may appear before M2
1
Mn2+ (oxidised (back)) to Mn3+ by MnO4− / equation

Sams Chemistry (16 decks)

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