Transition Metals Test PRi

Question 1

Q1a) Identify a suitable reagent, give the formula for copper containing species and write equation for reaction of [Cu(H2O)6]2+ ⟶ Pale Blue ppt.

Answer 1

Reagent – Ammonia
Species – [Cu(H2O)4(OH)2]
Equation – [Cu(H2O)6]2+ + 2NH3 ⟶ [Cu(H2O)3(OH)3] + 2NH4+

Question 2

Q1b) Reagent, species and equation for Reaction 2

Answer 2

Reagent – Ammonia in excess
Species – [Cu(H2O)2(NH3)4]2+
Equation – [Cu(H2O)4(OH)2] + 4NH3 ⟶ [Cu(H2O)2(NH3)4]2+ + 2H2O + 2OH-

Question 3

Q1c) Reagent, species and equation for Reaction 3

Answer 3

Reagent – Na2CO3
Species – [Cu(H2O)6]2+
Equation – [Cu(H2O)6]2+ + CO3(2-) ⟶ CuCO3 + 6H2O

Question 4

Q1d) Reagent, species and equation for Reaction 4

Answer 4

Reagent – HCl (Conc/xs)
Species – [Cu(H2O)6]2+
Equation – [Cu(H2O)6]2+ + 4Cl- ⟶ [CuCl4]2- + 6H2O

Question 5

Q2a) Explain why the reaction between I- ions and S2O82- ions is slow

Answer 5

They are both negatively charged

-ve ions repel one another

Question 6

Q2b) Other than having variable oxidation states, explain why Fe2+ ions are good catalysts for this reaction

Answer 6

Positive ions attract -ve ions in catalysed process

Question 7

Q2c) Write a half-equation for the reduction of S2O8(2-) ions to SO4(2-) ions

Answer 7

S2O8(2-) + 2e- ⟶ 2SO4(2-)

Question 8

Q2d) Construct an overall equation for the reaction between S2O8(2-) ions and I- ions

Answer 8

S2O8(2-) + 2I- ⟶ 2SO4(2-) + I2

Question 9

Q3a) Calculate the entropy change for the reaction between ammonia and oxygen

Answer 9

∆S = S(s products) - Σ(s reactants)

((4x211) + (6x189)) - ((4x193) + (5x205)) = 181 J/K/mol

Question 10

Q3b) Calculate a value for the Gibbs free-energy change (∆G), in kJ/mol, for the reaction between ammonia and oxygen at 600ºC

Answer 10

∆G = ∆H - T∆S 600ºC = 873K
∆G = -905 - 873(181x10-3) = -1063 kJ/mol

Question 11

Q3c) The reaction between ammonia and oxygen was carried out at a higher temperature.
Explain how this change affects the value of ∆G for this reaction

Answer 11

1) ∆G becomes more negative

2) Entropy change/∆S is +ve/T∆S gets bigger

Question 12

Q3d) Platinum acts as a heterogeneous catalyst in the reaction between ammonia and oxygen. It provides an alternative reaction route with a lower activation energy.
Describe the stages of this alternative route

Answer 12

1) Reactants absorbed onto Platinum surface/Pt provides surface/active site
2) Reaction on surface. Bond breaking/forming occurs on surface
3) Desorption of the product or words to that effect (wtte)

Question 13

Q3e) Deduce the change in oxidation state of Nitrogen, when NH3 is oxidised to NO

Answer 13

Oxidation state changes from -3 to +2 (or +5 overall)

Question 14

Q3f) When ammonia reacts with oxygen, Nitrous Oxide (N2O) can be produced instead of NO
Give an equation for this reaction

Answer 14

2NH3 + 2O2 ⟶ N2O + 3H2O

Question 15

Q4a) Explain, in terms of electrons, why the complexes are different colours. (You are NOT required to explain why the observed colours are red-violet and green)

Answer 15

1) In each of P & Q, oxidation state of Cr = +3
2) In each of P & Q, electron config is same/3d3
3) Ligands are different
4) Different energies of electrons/different orbital energies
5) Different wavelengths of light absorbed
6) Different wavelengths of light transmitted/reflected

Question 16

Q4b) Write an equation to show how the [Co(NH3)6]2+ ion reacts with 1,2-diaminoethane
Explain the thermodynamic reasons why this reaction occurs

Answer 16

1) 4 particles form 7 particles
2) Entropy increases
3) ∆H approx. 0/no net change in bond enthalpies
4) ∆G -ve
5) [Co(NH3)6]2+ + 3(NH2CH2CH2NH2) ⟶ [Co(NH2CH2CH2NH2)3]2+ + 6NH3

Question 17

Q4c) i) Draw displayed structure of Cisplatin. Show value of one of the bond angles at Platinum. State the charge if any

Answer 17

90º. Charge = 0

Question 18

Q4c) ii) When Cisplatin is ingested, an initial reaction involves one of the Chloride ligands being replaced by water.
Write an equation for this reaction

Answer 18

(NH3)2PtCl2 + H2O ⟶ [(NH3)2PtCl(H2O)]+ + Cl

Question 19

Q4c) iii) Suggest how the risk associated with the use of this drug can be minimised

Answer 19

Use in small amounts/short bursts/target application/monitor the patients

Question 20

Q4d) Explain, with the aid of equations, how and why Vanadium (V) oxide is used in the Contact Process

Answer 20

1) V2O5 + SO2 ⟶ V2O4 + SO3
2) V2O4 + 1/2 O2 ⟶ V2O5
3) Act as a catalyst
4) Speeds up overall reaction b/w SO2 & O2

Question 21

Q5a) Use information to calculate a value for the mass of FeSO4.7H2O in the sample of X
X dissolved in 250cm3 of water
After xs acid added, 25cm3 reacted with 21.3cm3 of 0.015M K2Cr2O7

Answer 21

1) Mol of Cr2O7(2-) = (21.3÷1000) x 0.0150 = 3.195x10-4
2) Cr2O7(2-) : Fe2+ = 1:6
3) Mol of Fe2+ = 6 x (3.195x10-4) = 1.917x10-3
4) Original is 250cm3 = (1.917x10-3) x 10 = 1.917x10-2
5) Mass of FeSO4.7H2O = (1.917x10-2) x 277.9 = 5.33g

Question 22

Q5b) Suggest ONE property of an impurity that would cause the calculated mass of FeSO4.7H2O in X to be greater than the actual mass of X.
Explain your answer

Answer 22

Impurity is a reducing agent

Question 23

Q6) Which one of the following reactions in aqueous solution has the most +ve change in entropy?
A - hexaaquacopper (II) + Ammonia ⟶ tetraaminodiaquacopper + Water
B - hexaaquacopper (II) + Chloride ⟶ tetrachlorocuprate + water
C - hexaaquacopper (II) + EDTA ⟶ EDTAcuprate + water
D - hexaaquacopper (II) + 1,2-diaminoethane ⟶ [Cu(EDTA)2(H2O2]2+ + Water

Answer 23

C – [Cu(H2O)6]2+ + EDTA4- ⟶ [Cu(EDTA)]2- + 6H2O

Question 24

Q7) The Vanadium does NOT have an oxidation state of +3 in:
A - [V(H2O)6]3+
B - [V(C2O4)3]3-
C - [V(OH)3(H2O)3]
D - [VCl4]3-

Answer 24

D – [VCl4]3-

Question 25

Q8) Which one of the following would lead to an inaccurate result?
A - Transferring weighed sample of Iron (II) Sulphate into a wet conical flask
B - Failing to measure accurately the volume of water used to dissolve each weighed sample of Iron (II) Sulphate
C - Transferring standard solution of K2Cr2O7 from its original container to burette using a wet beaker
D - Failing to measure accurately the volume of dilute H2SO4 added to the mixture before titration

Answer 25

C – Transferring standard solution of K2Cr2O7(2-) from its original container to burette using a wet beaker

Question 26

Q9) Which one of the following would lead to the greatest error in the calculation of the percentage of Iron (II) in the sample?
A - An error of 0.005g made when weighing out a sample of mass 0.987g
B - An end point error of 0.1cm3 in 25cm3
C - Error of 5cm3 when measuring out 25cm3 of dilute H2SO4
D - Using the average of the Titration values 25.4, 25.7 and 25.9 when the correct value is 25.5cm3

Answer 26

D – Using the average of the titration values 25.4, 25.7 and 25.9 when the correct value is 25.5cm3

Question 27

Q10)

Answer 27

D