3.2.5 Transition Metals (A2) Flashcards

Question

How can complex ions Show Optical Isomerism?

Answer 1

Complex Ions can show Optical Isomerism (type of Stereoisomerism) – where an ion can exist in two forms that are non-superimposable mirror images. This happens when three bidentate ligands, such as ethane-1,2-diamine (NH2CH2CH2NH2), co-ordinately bond with a central metal ion, such as Nickel

Answer 2

1) Cis-Trans Isomerism is another form of Stereoisomerism. Its a special case of E/Z Isomerism 2) Octahedral complexes w/4 monodentate ligands of one type and 2 monodentate ligands of another can show Cis-Trans Isomerism. If two odd ligands are opposite then its a Trans isomer. If they're next to each other its a Cis Isomer 3) Square Planar complex ions that have two pairs of ligands also show Cis-Trans Isomerism. E.g. Cisplatin (an effective Chemotherapy) and Transplatin (Ineffective)

Answer 3

1) When Ligands bond to ions, some of the orbitals gain energy. This splits 3d orbitals into two different energy levels 2) Electrons tend to occupy lower orbitals (ground state). To jump up to higher orbitals (excited states) they need energy equal to the energy gap, ∆E. They get this energy from visible light 3) The energy absorbed when electrons jump up from the ground state to an excited state can be worked out using ∆E = hv = ((hc) ÷ λ) 4) Amount of energy needed to make electrons jump depends on central metal ion and its oxidation state, the ligands and co-ordination #, as these affect size of the energy gap

Answer 4

``` ∆E = hv or ∆E = ((hc) ÷ λ) ∆E – Energy Absorbed h – Planck's Constant (6.63x10(-34) J/s) v – Frequency of light absorbed (Hertz, Hz) c – Speed of light (3x10(8) m/s) λ – Wavelength of light absorbed (m) ```

Answer 5

1) When visible light hits transition metal ion, some frequencies absorbed when electrons jump to higher orbitals. Frequencies absorbed depend on size of Energy Gap (∆E) 2) Rest of frequencies are transmitted or reflected. Transmitted or reflected frequencies combine to make the complementary colour of the absorbed frequencies – the colour you see 3) e.g. [Cu(H2O)6]2+ ions absorb light from red end of spectrum. Remaining frequencies combine to produce complementary colour – blue 4) If there are no 3d electrons or 3d sub-level is full, the no electrons will jump, so no energy will be absorbed. If no energy is absorbed, compound will look white or colourless

Answer 6

1) White light shone through a filter, which is chosen to only let through complementary colour (colour of light that is absorbed) 2) Light passes through sample to colorimeter, which calculates how much light was absorbed by the sample 3) The more concentrated a solution is, the more light it will absorb. You can use this measurement to work out the concentration of a solution of transition metal ions.

Answer 7

1) Ligand Substitution or Exchange | 2) A colour change

Answer 8

Co-ordination number doesn't change and neither does the shape

Answer 9

There is a change of Co-ordination number and change of shape

Answer 10

Ligand substitution reaction can be reversed easily, UNLESS the new complex ion is more stable than the old one

Answer 11

1) When ligand exchange reaction occurs, dative bonds broken and formed. Strength of those broken often v. similar to those being formed. So enthalpy change is usually v. small. e.g. Ethane-1,2-diamine and Nickel 2) Actually reversible, but equilibrium so far to right it is though to be irreversible – [Ni(NH2CH2CH2NH2)3]2+ more stable than [Ni(NH3)6]2+ 3) Instead, increase in stability (Chelate Effect), explains why multidentate ligands form more stable complexes than monodentate

Answer 12

Add them to Zinc Metal in an Acidic Solution 1) Solution turns from yellow to blue as Vanadium (V) is reduced to Vanadium (IV) 2) Solution then changes from blue to green as Vanadium (IV) becomes (III) 3) Finally, Vanadium (III) is reduced to Vanadium (II), and the solution changes from green to violet

Answer 13

1) Larger the redox potent., the less stable the ion will be, and more likely to be reduced 3) Redox Potentials are standard electrode potentials, measured with the reactants at a conc. of 1M (mol/dm3) against standard hydrogen electrode under standard conditions 4) Redox Potent. of an ion not always same as its Standard Electrode Potent. It can vary depending on the environment that the ion is in.

Answer 14

When added to Aldehydes, Tollens' oxidises it to a Carboxylic Acid and the Ag+ (Silver) ions are reduced to Silver Metal. Nothing occurs with Ketones

Answer 15

Redox Titrations

Answer 16

1) Measure out quantity of reducing agent (e.g. Aqueous Fe2+ ions) using a pipette, and put it in a conical flask 2) Using a measuring cylinder, add approx. 20cm3 of dilute sulphuric acid to the flask 3) Add Oxidising agent to the reducing agent using a burette 4) Oxidising Agent reacts with reducing agent. Reaction will continue until all of reducing agent is used up. Next drop will give the mixture the colour of oxidising agent 5) Stop when mixture in flask just becomes tainted with colour of oxidising agent (end point) and work out Titre (rough titration) 6) Repeat more accurately, do a few more until 2 or more are within 0.10cm3 of each other

Answer 17

1) Aqueous Potassium Manganate (VII) 2) It contains PURPLE Manganate (VII) ions. 3) Strong Acidic Conditions

Answer 18

1) Work out # of moles of (MnO4)- added to flask = (Conc x vol) ÷ 1000 = (0.02x27.5) ÷ 1000 = 5.5x10(-4) 2) Look at balanced equation to work out # of mol of C2O4 react with every mol of MnO4 – 5mol of C2O4 react with 2 mol of MnO4. Mol of C2O4 = (5.5x10(-4) x 5) ÷ 2 = 1.38x10(-3) mol 3) Work out # of mol of C2O4 that would be in 1000cm3 (1dm3) of solution (this is concentration) – 25cm3 contained 1.38x10(-3) mol 1000cm3 would contain ((1.38x10(-3)) x 1000) ÷ 25 = 0.552 mol of C2O4. So conc = 0.552 mol/dm3

Answer 19

1) By Changing Oxidation State 2) Change Oxidation states by gaining of losing electrons within d orbitals. This means they can transfer electrons to speed up reactions

Answer 20

1) Heterogeneous Catalyst is one that is in a different phase from reactants (in different physical state), e.g. in Haber Process gases passed over solid iron catalyst 2) Reaction happens on active sites located on surface of heterogeneous catalyst. Increasing SA of catalyst, increasing number of molecules that can react at the same time, increasing rate of reaction 3) Support mediums often used to make area of catalyst as large as possible. Help to minimise cost of reaction, only small coating of catalyst needed to provide large surface area

Answer 21

1) Impurities in reaction mixture can bind to catalyst's surface and block reactants from being absorbed. This process is called Catalyst Poisoning 2) Catalyst Poisoning reduces Surface Area of Catalyst available to reactants – slowing reaction 3) Poisoning increases cost of chemical process because less product can be made in a certain time or with certain amount of energy. Catalyst may need replacing or regenerating, which cost money

Answer 22

1) Homogeneous catalysts in same phase as reactants 2) Work by combining reactants to form intermediate species, which then form products and re-form catalyst 3) Enthalpy profile has two humps in it, corresponding to the two steps of reaction 4) Activation Energy needed to form Intermediates lower than needed to make products directly 5) Catalyst always Re-Forms, so it can carry on catalysing reaction

Answer 23

When Product Catalyses Reaction e.g. Mn2+ It's an Autocatalysis reaction because Mn2+ is a product of the reaction it acts as a catalyst for. Means as reaction progresses and amount of product increases, reaction speeds up

Answer 24

Transition metal compounds dissolved in water. In general, 6 water molecules form co-ordinate bonds with trans metal, e.g. hexa-aqua iron (II) [Fe(H2O)6]2+

Answer 25

1) In solution containing metal-aqua 2+ ions, reaction between metal-aqua ion and the water – hydrolysis 2) Metal-aqua 2+ ions release H+ ions, so acidic solution is formed 3) Only slight dissociation, so solution weakly acidic 4) Metal-aqua 3+ ions react in same way, but dissociate more than 2+ ions, so form more acidic solutions

Answer 26

Adding OH- ions to Metal-aqua ions produces insoluble metal hydroxides: 1) In water, metal-aqua 3+ ions form equilibrium. If you add OH- ions, H3O+ ions are removed, shifts equi to right 2) Now another equilibrium is set up in the solution. OH- ions again remove H3O+ ions from solution, pulling equi to right 3) Happens one last time – now left with insoluble uncharged metal hydroxide 4) Same thing happens with Metal-aqua 2+ ions, except only 2 steps instead of 3

Answer 27

When mixed with base, e.g. NaOH, acts as Brønsted-Lowry Acid, donates H+ ions/protons to OH- ions forming soluble compound. When acid is present, acts as Brønsted-Lowry Base and accepts H+ ions/protons from H3O+ ions in solution