AQA A Level Chemistry - Paper 3 Exam Questions With Well Elaborated Solutions

AQA A Level Chemistry - Paper 3 Exam Questions With Well Elaborated Solutions What is delta E in transition metals? - ANSWER The difference in energy of the excited state and the ground state of the electron What happens if an electron absorbs energy equal to the energy gap of delta E? - ANSWER it can move to occupy the higher energy orbitals. This is called an excited electronic state. What is the formula for delta E - ANSWER What do these stand for in the formula delta E=hv or delta E = (hc)/λ - ANSWER ν is the frequency of light in hertz h is planck's constant c is the speed of light in ms-1 λ is the wavelength of the light in metres What affects delta E in transition metals? - ANSWER -the metal ion -its oxidation state -its ligands -its coordination number. What happens to a d-sub shell metal when there are no ligands present? - ANSWER NO d sub-shell splitting factors affecting the colour of transition metal ions: - ANSWER ligands and their geometries what happens when a transition metal ion is in light? - ANSWER it will absorb the frequencies which correspond to the d sub-shell energy gap Why does Fe(III) often appear yellow or orange when concentrated? - ANSWER This is because hexaaqua iron(III) is quite acidic, and will lose protons to become Fe(H2O)5(OH-) (and this is yellow). If you're asked what colour hexaaqua iron(III) is, what colour should you say? (Despite the fact that hexaaqua iron (III) is yellow when concentrated) - ANSWER purple Features of spectroscopy (transition metals) - ANSWER 1- White light shines through a coloured filter to remove everything but that colour of light 2- This light then falls on a transition metal sample solution 3- The more light it absorbs, the higher the concentration of the solution The energy gap from the wavelength of absorbed light depends on: - ANSWER -The metal ion -The metal's oxidation state -The ligands surrounding the metal -The coordination number What do you need to form a calibration curve (transition metal Spectroscopy)? - ANSWER measure absorbances of known solutions what colour is {Cu(Cl)4}2+ - ANSWER yellow what colour is {V(H2O)6}2+ - ANSWER violet what colour is {V(H2O)6}3+ - ANSWER green what colour is {Cu(H2O)6}2+ - ANSWER deep blue What colour is {Co(H2O)6}2+ - ANSWER pink What colour is {Co(NH3)6}2+ - ANSWER straw-coloured Vanadium (V) colour - ANSWER Yellow (VO2)+ Vanadium (IV) colour - ANSWER blue (VO)2+ Vanadium (III) colour - ANSWER green (V)3+ Vanadium (II) colour - ANSWER violet (V)2+ When reducing vanadium; what colour does the solution become when turning from Vanadium (V) to Vanadium (IV) and why? - ANSWER The solution goes from yellow to green to blue. It turns green, because (Yellow + blue = green) What metal is used to reduce Vanadium? - ANSWER Zinc redox potential - ANSWER the tendency of a molecule to acquire electrons standard redox potentials are quoted relative to - ANSWER a standard hydrogen electrode under standard conditions. What can redox potentials depend on? - ANSWER Ligands or pH What conditions are needed to measure standard redox potentials? - ANSWER Standard redox potentials are measured in aqueous solution. What affect does changing the ligand have on redox potentials? - ANSWER Changing the ligands will alter the redox potential depending on the bond strength to the metal. What does a higher concentration of H+ mean for redox potentials usually? - ANSWER Usually, a higher concentration of H+ means a higher redox potential. What type of solution does zinc have to be in to reduce vanadium? - ANSWER Different ions of vanadium can be prepared by successive reduction with zinc in acid solution. What conditions do KMnO4 need to be in to be reduced - ANSWER in acidic conditions, so you need to add an excess of sulfuric acid. what colour does KMnO4 go when reduced? - ANSWER colourless What is concordant results? - ANSWER Concordant titrations are titrations that give the same result, no more than 0.10cm3 apart. How do catalysts work? - ANSWER They provide an alternative reaction pathway with a lower activation energy What is a homogenous catalyst? - ANSWER a catalyst in the same phase as the reactants Why does the enthalpy profile of a catalysed reaction have two peaks? - ANSWER First, the catalyst is either oxidised or reduced. Then, the reverse happens. Both of these steps have a lower activation energy than the uncatalysed reaction, so this pathway is faster. What is a heterogenous catalyst? - ANSWER A catalyst that is in a different phase from the reactants Autocatalysis - ANSWER a reaction in which a product is the catalyst. What reaction is Mn2+ the (auto)catalyst of? - ANSWER The reaction between [MnO4]- and [C2O4]2- (homogenous catalyst) How is Mn2+ catalytic in the reaction between [MnO4]- and [C2O4]2-? - ANSWER 1) Mn2+ is catalytic because it reacts with MnO4- to make Mn3+.