Transition Elements Flashcards
variable oxidation states catalysts Forming coloured ions Forming Complex ions
CATALYST AND VARIABLE OXIDATION STATE QUESTIONS
CATALYST AND VARIABLE OXIDATION STATE QUESTIONS
Explain what is meant by the term ‘heterogenous’
Give an example of a reaction where a heterogenous catalyst is used? [2]
different phase/ state to the reactants 1
any one from:
Haber Process 1
Contact Process
In the Haber Process, for the manufacture of ammonia a catalyst is required
Identify the catalyst used in this reaction? [1]
Iron / (Fe) 1
Heterogenous catalysts can become poisoned by impurities in the reactants
Give an example of an impurity, and explain how it poisons the catalyst? [3]
sulfur compound ( allow sulfur ) 1
it strongly adsorbs onto catalyst active sites 1
or (it blocks the reactants from being adsorbed)
poison reduces the surface area of the catalyst 1
Explain what is meant by the term ‘homogeneous’ Suggest why transition metals are good catalysts? [2]
same phase / state to the reactants 1
they have variable oxidation states 1
In aqueous solution S2O8[2-] ions are reduced to SO4[2-] ions using I- ions
Write an equation for this reaction? [1]
S2O8 [2-] + 2I- ——–> 2SO4[2-] + I2 1
Suggest why the reaction between S2O8 [2-] and I- is very slow without using a catalyst? [1]
Aqueous iron ions can be used to catalyse this reaction
Write two equations to show the role of the catalyst? [2]
both ions are negative, so they repel each other 1
S2O8 [2-] + 2Fe[2+] ——> 2SO4 [2-] + 2Fe[3+] 1
2I- + 2Fe[3+] ——-> I2 + 2Fe[2+] 1
Describe what is meant by the term ‘autocatalysis’? [1]
when one of the products catalyses the reaction 1
Describe and explain why the reaction between sodium ethanediote (Na2C2O4 ) and potassium manganate (VII) is initially slow but the overtime increases?
Write equations to show the reaction [6]
(slow initially) as both the ions are negative 1
so ions repel each other 1
(overtime) Mn[2+] produced acts as an autocatalyst 1
2MnO4 - +5C2O4[2-] +16H+ > 2Mn[2+] +8H20 +10CO2 1
MnO4 - + 4Mn[2+] + 8H+ —–> 5Mn[3+] + 4H2O 1
2Mn[3+] + C2O4[2-] ——-> 2Mn[2+] + 2CO2 1
Describe and explain why the reaction between sodium ethanediote (Na2C2O4 ) and potassium manganate (VII) is initially slow but the overtime increases?
Write equations to show the reaction [6]
(slow initially) as both the ions are negative 1
so ions repel each other 1
(overtime) Mn[2+] produced acts as an autocatalyst 1
2MnO4 - +5C2O4[2-] +16H+ > 2Mn[2+] +8H20 +10CO2 1
MnO4 - + 4Mn[2+] + 8H+ —–> 5Mn[3+] + 4H2O 1
2Mn[3+] + C2O4[2-] ——-> 2Mn[2+] + 2CO2 1
( NB: If struggling work out both half equations first then combine them to help with balancing! )
i) What is meant by the term ‘active sites’ in relation to catalysts? [1]
ii) Describe how the number of active sites can be increased for a given mass of catalyst? [1]
iii) Describe how the efficiency of a catalyst can be reduced? [1]
i) region on catalyst where the reactants are (adsorbed) onto the surface 1
ii) use a support medium / powdered 1
iii) catalytic poisoning / another species is adsorbed onto surface(irreversibly) 1
When petrol is burned in cars, CO, CO2, oxides of nitrogen and water are produced. Catalytic converters can be used to reduce the emissions of toxic gases
Write an equation for the reaction which occurs in a catalytic converter? [1]
Identify a transition metal that could be used in catalytic converters? [1]
2CO + 2NO ——> 2CO2 + N2 1
Pt / Rh / Pd 1
Explain why transition metals that bind strongly to the active sites are not good catalysts? [1]
reactants cannot move, OR products not (desorbed) 1
Suggest a reason why the reaction between I- (iodide ions) and S2O8 [2-] (persulfate ions), has a very high activation energy? [1]
Both ions are negative OR ions repel each other 1
i) Write an equation to show the reaction of I- ions and S2O8 [2-] ions? [1]
ii) Write two equations to illustrate the effect of adding an Fe [2+] catalyst to the reaction? [2]
i) S2O8[2-] + 2I- ——–> 2SO4[2-] + I2 1
ii) S2O8[2-] + 2Fe[2+] ———> 2SO4[2-] + 2Fe[3+] 1
2I- + 2Fe[3+] ———> I2 + 2Fe[2+] 1
State two reasons why an inert medium is often used to support heterogeneous catalysts? [2]
1) to increase the surface area 1
2) to minimise the costs 1
State three important feature needed for the function of a heterogeneous catalyst? [3]
has active sites OR allows adsorption onto surface 1
weakens bonds of reactants 1
increases surface concentration 1
The Haber process uses a heterogeneous catalyst to produce ammonia
Write a different equation for a process that uses a heterogeneous catalyst? [1]
Identity the catalyst used for this reaction and state the name of the process? [2]
2SO2 + O2 ——–> 2SO3 1
V / vanadium, allow (V2O5) 1
Contact Process 1
Describe and explain how catalysts are used in the Contact Process, with the aid of equations? [2]
Give one use of SO3 produced by this reaction? [1]
V2O5 + SO2 ——–> V2O4 + SO3 1
V2O4 + 1/2 O2 ———-> V2O5 ( catalyst reformed) 1
used to make sulfuric acid / H2SO4 1
Vanadium ions can have variable oxidation states
For each of the following identify the colour of the ion produced? [2}
a) VO2 [2+] b) VO [2+] c) V [3+] d) V [2+]
a) yellow
b) blue 1 mark for each two
c) green correct answers
d) violet, (DO NOT allow purple)
Vanadium can be reduced by experiment
State a reagent and a condition needed? [2]
reagent: zinc 1
condition: acidic conditions/ add HCl 1
FORMATION OF COLOURED IONS QUESTIONS
FORMATION OF COLOURED IONS QUESTIONS
State three changes to a transition metal that would result in a change in colour? [3]
change in oxidation state 1
change in coordination number / number of ligands 1
change in type of ligand 1
Colourimetry can be used to find the concentrations of transition metal ions
Suggest why a coloured filter is used? [1]
Suggest why colourimetry may be chosen as a preferred method over titration? [1]
To select the colour / wavelength that is (most strongly) absorbed (by the sample) 1
(Faster) to analyse extracted samples than by titration 1
Explain why transition metal complexes are coloured?[2]
Energy is absorbed from(visible light) 1
when electrons are promoted to a higher energy level 1
Briefly describe how you would construct a calibration curve? [3]
prepare a range of solutions with known concentrations 1 Measure absorbance 1 Plot graph( concentration against absorption ) 1
Frequency absorbed can be determined by the equation E= hv
State the meaning of E and the change it represents? [1]
(E) is the energy absorbed, when electron is promoted to higher energy level OR
moved to exited state 1
Give the noble gas electron configuration of the following
Cu +
Cu [2+]
State which ion will produce a coloured ion, and why? [4]
Cu + [Ar] 3d10 1
Cu [2+] [Ar] 3d9 1
Cu [2+] 1
Has a partially filled d-sub shell 1
