Transition Metals

Question 1

Explain why complexes formed from transition metal ions are coloured.

Answer 1

M1 absorb (some) wavelengths/frequencies/colours/energies of (visible) light

M2 to promote/excite electrons in d-orbitals
Allow d-subshell / d-energy level / d-electrons
Reterence to a can appear anywhere in the answer

М3 remaining/complementary wavelengths/frequencies/colours/energies of (visible) light reflected/transmitted (to give colour seen)

Question 2

(c) Describe how a calibration graph is produced and used to find the concentration of the iron(III) complex.

Answer 2

M1 measure absorbance for (a range of known concentrations
Insist on description of taking measurements
M2 plot graph absorbance v concentration
Allow concentration v absorbance
M3 read value of concentration for the measured absorbance from this

Question 3

Solid sodium chloride reacts with concentrated sulfuric acid.
Give an equation for this reaction.
State the role of the sulfuric acid in this reaction.

Answer 3

NaCI + H2SO4 -> NaHSO4 + HCI
Allow 2 NaCI + H2SO4 -> Na2SO4 + 2 HCI
Proton donor
Allow (Bronsted-Lowry) acid

Question 4

Fumes of sulfur dioxide are formed when sodium bromide reacts with concentrated sulfuric acid.
For this reaction
give an equation give one other observation state the role of the sulfuric acid.

Answer 4

Question 5

Answer 5

Question 6

Answer 6

Question 7

Suggest two ways that the student could reduce the percentage uncertainty in the measurement of the volume of sodium thiosulfate solution, using the same apparatus as this experiment.

Answer 7

Use more of the alloy
Use a lower concentration of the thiosulfate solution/lower mass of
Massoos to make solution

Question 8

Copper(I) iodide is a white solid.
Explain why copper(I) iodide is white

Answer 8

Full (3)d (sub)shell or (3)d10
No (d-d) transitions possible/ cannot absorb visible/white light

Question 9

Answer 9

Question 10

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 10

Reactants) adsorbed onto the (platinum surface) / (platinum) provides a surface active sites
Reaction (on the surface) or bond breaking(weakening) / bond making
occurs on he surace
Desorption (of the product) or wtte

Question 11

(d) Heating NH VO produces vanadium(V) oxide, water and one other product.
Give an equation for the reaction.

Answer 11

(d) 2 NH4VO3 -> V205 + H20 + 2NH3

Question 12

Answer 12

Question 13

Answer 13

A) COVALENT

Question 14

Explain why colorimetry cannot be used to determine the concentration of solutions containing [CuCl2]-
In your answer refer to the electron configuration of the metal ion.

Answer 14

(f) (3)d10 or has full (3)d (sub) shell/orbital
Penalise incorrect principal quantum number
It is colourless/cannot absorb (frequencies of) visible light

Question 15

Answer 15

Question 16

Multidentate in terms of EDTA meaning
Ligand in terms of EDTA meaning

Answer 16

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(Il) ions.

Question 17

Answer 17

Question 18

Answer 18

Question 19

Answer 19

Question 20

Four characteristics of transition metals

Answer 20

• variable oxidation states
• form coloured compounds
• form complexes with ligands
• acts as a catalyst

Question 21

Why is manganate ions acidified in titrations

Answer 21

Stop the formation of MnO2/ ensures all MnO4- reacts to form Mn2+

Also because MnO4- acts as the best oxidising agent in acidic conditions

Question 22

How would you ensure the reliability of the result in a titration

Answer 22

Repeat titration and take an average of concordant results

Question 23

Suggest one way in which the reliability of this analysis could be improved in a titration involving iron from a blast furnace containing carbon where in the steel making process oxygen is blown through molten of impure iron.

Answer 23

Analyse several samples from different parts of the molten iron.

Question 24

Why does dilute HCL not be used to acidify MnO4-

Answer 24

Manganate would oxidise/ react with Cl- ions

Question 25

Why is it important that MnO4- is not reduced to MnO2 during a titration

Answer 25

Cant see end point due to brown colour Larger titre than expected

Question 26

Suggest one reason why a 0.02 mol dm-3 solution of potassium manganate(VII) does not need to be kept away from flammable material

Answer 26

Solution dilute

Question 27

The student found that the calculated mass of FeSO,. 7H2O was greater than the actual mass of the sample that had been weighed out. The student realised that this could be due to the nature of the impurity. Suggest one property of an impurity that would cause the calculated mass of FeSO..7H2O in X to be greater than the actual mass of X. Explain your answer.

Answer 27

Impurity is a reducing agent/ reacts with dichromate/ impurity is a version of FeSo4 with fewer than 7 H2O Such tha for a given mass, the impurity would react with more dichromate than a similar mass of FeSo4.7H2O

Question 28

When dissolved in dilute sulfuric acid, the number of moles of ethanedioate ions in a pigment can be determined by titration with acidified potassium manganate(VII). Explain why the titration of a sample of iron(Il) ethanedioate would require a different amount of potassium manganate (VII) than a titration of an equimolar amount of copper(Il) ethanedioate.

Answer 28

MNO4- will oxidise the iron ion and ethanedioate ions MnO4- does not oxidise copper 2+ ion

Question 29

Q7. (a) The iron(Il) ions in well-water can be removed by oxidation using potassium manganate(VII) in alkaline solution. A mixture containing solid iron(III) hydroxide and solid manganese(IV) oxide is formed. These solid products can be removed by filtration under reduced pressure. Draw a diagram of the apparatus used for this filtration. Do not include the apparatus used to reduce the pressure.

Answer 29

Question 30

In practice, a slight excess of potassium manganate(VIl) is used to treat the well-water. Although this treated water is safe to drink, this excess of potassium manganate(VIl) is undesirable. Suggest one reason, other than colour, why the excess is undesirable.

Answer 30

Unpleasant taste

Question 31

Suggest one reason why colour of potassium Manganate solution can be a source of error when using a volumetric flask to prepare a standard solution

Answer 31

Difficult to see the meniscus

Question 32

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 32

Ligands are different Different energies of (d) electrons / different split of (d) electron energy levels different energy gap of (d) electrons / different (d) orbital energy Different wavelengths / frequencies / energies of light / colours (of light) are absorbed (by the d electrons) Reference to emission and / or uv light but not to visible loses M5 and M6 Different wavelengths / frequencies / energies of light / colours (of light) are transmitted / reflected

Question 33

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

Answer 33

Question 34

Define Coordinate bond Brønsted-Lowry acid Lewis acid Bidentate ligand

Answer 34

1. A shared electron pair or covalent bond. Both electrons from one atom 2. A proton donor 3: a lone or electron pair acceptor 4. Tow atoms/points of attachment, each donating a lone electron pair

Question 35

Deduce the formula of the compound formed when ethane-1,2-diamine is treated with an excess of hydrochloric acid

Answer 35

Question 36

Answer 36

Question 37

(C) The frequency, v, of light absorbed by a transition metal complex ion can be determined using the relationship A = hv. State what is meant by the symbols A and h. Give three factors which result in a change in the frequency of light absorbed as a result of the reaction of a complex ion.

Answer 37

AE; energy absorbed by electron, ground to excited state (QoL) h; Planck's constant or a constant Change in Oxidation state Ligand Co-ordination number

Question 38

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

Answer 38

Too many electrons in d-sub shell

Question 39

Answer 39

Question 40

Suggest why coloured filters are used

Answer 40

To select the colour / frequency / wavelength that is (most strongly) absorbed

Question 41

Why may colorimetric be used instead of titration

Answer 41

Quicker to analyse extracted samples than by titration / uses smaller volumes of solution

Question 42

Why is Fe2+ good catalysts for reaction with I- and S2O42-

Answer 42

Variable oxidation states Positive ions attract negative ions in catalysed process Activation energy decreases as alternative route provided

Question 43

The energy change shown in the diagram represents the energy of red light and leads to a solution that appears blue. Blue light has a higher frequency than red light. Suggest whether the energy change A will be bigger, smaller or the same for a transition metal ion that forms a red solution. Explain your answer.

Answer 43

Bigger blue light would be absorbed OR light that has greater energy than red light would be absorbed

Question 44

Answer 44

Question 45

Answer 45

Tetrahedral 109.5