15.3 2 Homogeneous catalysis Flashcards
homogeneous catalyst
same phase as reactants
either all gases or more often all in aqueous solution
far less common in industry
key feature of homogeneous catalysis
formation of an intermediate species for which a specific formula can be written
persulfate ion /peroxodisulfate ion
S2O82-
Persulfate ion + iodine
S2O82-+2I-=2SO42-+I2
Acts as an oxidising agent
slow at room temp as both are negative so repel reaction faster with Fe2+ act as catalyst
all aqueous phase
step one with persulfate and iodide
S2082- + 2Fe2+ = 2SO42- + 2Fe3+
step two
2Fe2+ + 2I- = 2Fe2+ + I2
uses opposite charges
regeneration so can repeat steps
what if use Fe3+ ions
2Fe3+ + 2I- =2Fe2+ I2
S2O82- + 2Fe2+ =2SO42- + 2Fe3+
same two reactions different order
titrations with potassium manganate (V11)
In acidic conditions act as an oxidising agent
oxidation of ethanedioate ions by potassium managanate (V11)
2MnO4- +5C2O42- +16H+ =2Mn2+ + 5CO2 +8H2O
Both neg charged
as more potassium manganate is added reaction rate increases
at start of titration
purple colour of potassium manganate (V11) solution takes time to disappear
in middle of titration
solution now disappears more quickly as more Mn2+ ions to catalyse reaction
end of titration
no ethandioate ions left to react so the remaining potassium manganate (V11) solution gives pink colour
autocatalysis
when a product of a reaction acts as the catalyst of the reaction
reaction rate will increase as time goes on
1) Slow decrease in reactant concentration as uncatalyzed initially 2) reactant concentration decreases more rapidly as reaction rate increases because of catalysis 3) reactant concentration slowly decreases as there is little reactant left
see
graph +image in book
