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44 Cards in this Set
- Front
- Back
What is a transition metal? |
A metal that forms one or more stable ions with a partially filled d sub-shell |
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Why are zinc and scandium not transition metals? |
Zn forms Zn2+ ion which has a full d sub-shell Sc forms Sc3+ which has an empty d sub-shell |
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What is the colour of V2+ |
violet |
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What is the colour of V3+? |
Green |
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What is the colour of VO(2+)? |
blue |
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What is the colour of VO2(+)? |
yellow |
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What are the physical properties of transition metals? |
High melting and boiling points High density similar ionic radii |
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What are the chemical properties of transition metals? |
Form complex ions Form coloured ions make good catalysts have variable oxidation states |
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What is the colour of Ni2+? |
green |
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What is the colour of Mn2+? |
pale pink |
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What is the colour of MnO4-? |
purple |
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Why do transition metals have variable oxidation states? |
Energy levels of the 3d and 4s subshells are close to one another, so diff number of electrons can be lost using similar amounts of energy |
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What is a complex ion? |
A central transiiton metal ion surrounded by co-ordinately bonded ligands |
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What is a ligand? |
A species that forms a co-ordinate bond with a central metal ion |
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What is the bond angle in a: tetrahedral complex octahedral complex square planar complex? |
109.5 90 (and 180) 90 |
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Why are EDTA complexes more stable? |
Central ion held firmly by many co-ordinate bonds
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Why are cyanide ions in a metal complex not dangerous? |
Strongly bound to metal ion |
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What are the uses of EDTA? |
Antitode to metal poisoning - trap and remove metal ions remove calcium ions from blood during transfusions to prevent clotting remove calcium ions from hardwater to prevent clogging of pipes |
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What is the role of haemoglobin? |
Transport oxygen around the body in the blood |
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Describe the structure and function of haemoglobin? |
Central Fe2+ ion 4 co-ordinately bonded nitrogen atoms from a porphydrin molecule also coordinately bound globin molecule (protein) In lungs, oxygen forms a weak co-ordinate bond forming oxyhaemoglobin where needed, oxygen displaced by water to form deoxyhaemoglobin |
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Why do transition metal complexes have colour? |
Absorb particular wavelengths of light d electrons excited to a higher energy d orbital remaining wavelengths reflected wavelength absorbed dictated by energy gap between d orbitals when d-d splitting occurs |
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Why does Sc3+ not have a colour? |
No electrons in d orbitals to excite no wavleengths absorbed |
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Why does Zn2+ not have a colour? |
No vacant d orbital for a d electron to be exicited |
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How can spectrometry be used to determine the conc of a complex ion solution? |
Pass white light through a filter Pass filtered light through the sample and a colorimeter Produce calibration graph using samples of known conc (straight line as absorbance is prop to conc at low concs) compare absorbance with graph |
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What are the advantages of spectrometry? |
Easy to take many readings and can determine conc quickly doesn't use up sample/interfere with reactions |
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How can you reduce dichromate ions and what is the product |
zinc and dilute hcl green Cr3+ ions |
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How can you reduce Cr3+ ions and what is the product? |
zinc and hcl in an inert atmosphere as blue Cr2+ is unstable |
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How can you oxidise Cr3+ ions? What is the product? |
hydrogen peroxide in alkaline conditions yellow CrO42- ions |
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Why, when orange dichromate ions are reduced, is the solution not violet (the colour of [Cr(H2O6]3+)? |
Ligand substitution occurs by chloride ions in dilute HCl used to reduce |
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How do you prevent oxidation of something? |
Stablilise through the addition of acid |
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Why do you have to store Fe2+ ions in acidic solution? |
Prevent oxidation |
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Why do you need dilute acid for reduction of dichromate ions? |
Enough H+ ions for all dichromate to be reduced |
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Why do transition metals make good catalysts? |
Variable oxidation states transfer electrons to speed up reactions |
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How do heterogenous catalysts speed up rate of reaction? |
Reactants adsorb onto surface of the catalyst; reactants held in position/in higher conc on surface so more likely to be a successful collision; weakens bond/leads to fragmentation and lowers activation energy |
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Why is catalyst poisoning expensive? |
Less product produced as slower rate of reaction catalyst has to be replaced |
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Describe 3 reactions that use a heterogenous catalyst |
N2 + 3H2 ----> 2NH3 (Fe(s) catalyst) SO2 + O2 ---> SO3 (V2O5) H2 + CO ----> CH3OH (Cr2O3) |
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What determines the suitability of a catalyst to a reaction? |
How strongly adsorbed reactants are too strong and prodcut not released too weak and reaction cant take place |
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What poisons the catalyst in a catalytic converter? |
Lead |
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What poisons the catalyst in the Haber process? |
sulfur |
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How do homogenous catalysts work? |
Produce intermediate species/provide alternative reaction route of lower activation energy |
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How do you reduce catalyst poisoning? |
Purify the reactants |
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Why is the reaction between peroxidisulfate nad iodide slow? |
repulsion between negativ eions unlikely colision |
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How can you test for the presence of iodine? |
starch |
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What is meant by autocatalysis? |
Product of a reaction acts as the catalyst |