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AQA Chemsitry Exam Questions > Transition Metals > Flashcards

Transition Metals Flashcards

1
Q

Explain why complexes formed from transition metal ions are coloured.

A

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)

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2
Q

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

A

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

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3
Q

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

A

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

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4
Q

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.

A
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5
Q
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6
Q
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7
Q

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.

A

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

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8
Q

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

A

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

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9
Q
A
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10
Q

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.

A

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

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11
Q

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

A

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

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12
Q
A
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13
Q
A

A) COVALENT

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14
Q

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.

A

(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

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15
Q
A
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16
Q

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

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(Il) ions.

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17
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18
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19
Q
A
20
Q

Four characteristics of transition metals

A
  • variable oxidation states
  • form coloured compounds
  • form complexes with ligands
  • acts as a catalyst
21
Q

Why is manganate ions acidified in titrations

A

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

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

22
Q

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

A

Repeat titration and take an average of concordant results

23
Q

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.

A

Analyse several samples from different parts of the molten iron.

24
Q

Why does dilute HCL not be used to acidify MnO4-

A

Manganate would oxidise/ react with Cl- ions

25
Q

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

A

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

26
Q

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

A

Solution dilute

27
Q

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.

A

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

28
Q

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.

A

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

29
Q

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.

A
30
Q

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.

A

Unpleasant taste

31
Q

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

A

Difficult to see the meniscus

32
Q

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.)

A

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

33
Q

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.

A
34
Q

Define

Coordinate bond
Brønsted-Lowry acid
Lewis acid
Bidentate ligand

A
  1. A shared electron pair or covalent bond. Both electrons from one atom
  2. A proton donor
    3: a lone or electron pair acceptor
  3. Tow atoms/points of attachment, each donating a lone electron pair
35
Q

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

A
36
Q
A
37
Q

(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.

A

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

38
Q

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

A

Too many electrons in d-sub shell

39
Q
A
40
Q

Suggest why coloured filters are used

A

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

41
Q

Why may colorimetric be used instead of titration

A

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

42
Q

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

A

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

43
Q

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.

A

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

44
Q
A
45
Q
A

Tetrahedral
109.5

AQA Chemsitry Exam Questions (34 decks)

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