must know equations - TM

what do we need to know about vanadium

Oxidation state	Species present	Colour
V +5	VO2+	yellow
V +4	VO2+	blue
V +3	V3+	green
V +2	V2+	violet

cotton wool plug put in tube to keep air out

must be reduced by zinc in acidic solution

what do we need to know about Tollens Reagent

• Tollen's reagent which contains [Ag(NH₃)₂]⁺ - silver mirror formed in presence of aldehydes as Ag +1 reduced to Ag (0), aldehyde oxidised to carboxylic acid

half equation for MnO4-

MnO₄^- + 8H+ + 5e- ——> Mn2+ + 4H₂O

MnO4- (purple) is self indicating = colourless to pink is endpoint

colourless = Mn2+

so when MnO4- just in excess (neutralisation point

Fe2+ half equation

Fe²⁺ —→ Fe3+ +e-

if we don’t have Fe2+ = react Fe element with sulfuric acid to oxidise it

react Fe3+ with Zn to reduce it (Zn must be removed)

full equation for Fe and MnO4-

MnO₄^- + 8H+ + 5Fe2+ ——> Mn2+ + 4H₂O + 5Fe3+

C2O4^2- half-equation

C₂O₄^2- ——> 2CO₂ + 2e-

full equation

2MnO₄^- + 16H+ + 5C₂O₄^2- ——> 2Mn2+ + 8H₂O + 10CO₂

what is autocatalysis and equations for Mn in the C2O4^2-

autocatalysis = catalyst is one of the reaction products

4Mn²⁺ + MnO₄^- + 8H+ —> 5Mn³⁺ + 4H₂O

2Mn³⁺ + C₂O₄^2- —> 2CO₂ + 2Mn²⁺

what is and how do heterogenous catalysts work

catalyst is in different phase than reactants

reaction takes place on the active sites

reactants adsorbed onto active site of catalyst, bonds weaken, products desorb

how to maximise SA and minimise cost of heterogenous catalyst

spread catalyst on inert support medium using thin coating

or have catalyst be fine powder

more efficient

heterogenous catalyst poisoning

impurities block the active sites by binding/poisoning the catalyst and reduce the SA of the catalyst

reduces efficiency = expensive to replace

what catalyst is used in Haber process

iron catalyst - heterogenous as it is solid and the H₂ N₂ NH₃ (reversible reaction)

only lasts around 5 years before sulfur poisoning occurs

catalyst in Contact process

heterogenous catalyst in manufacture of sulfuric acid

2SO₂ + O₂ <=> 2SO₃

vanadium oxide is the catalyst

V₂O₅ + SO₂ → SO₃ + V₂O₄

V₂O₄ + 1/2O₂ → V₂O₅

homogenous catalyst we need to know

overall equation - all are in aqueous state

S₂O₈^2- + 2I^- → 2SO₄^2- + I₂

high Ea as negatively charged ions repel

two equations

S₂O₈^2- + 2Fe²⁺ → 2SO₄^2- + 2Fe³⁺

low Ea as oppositely charged ions attract

2Fe³⁺ + 2I^- → 2Fe²⁺ + I₂

when using MnO4- in redox titration, what acid should be used

dilute sulfuric acid

MnO4- is oxidising agent

what are the unsuitable acids and why are they unsuitable

hydrochloric - MnO4- would oxidise the Cl- to Cl2 so affect volume needed for titration

conc sulfuric or nitric acid are oxidising agents themselves so affect volume needed for titration

ethanoic acid is weak acid - not enough H+ ions provided

what is homogenous catalyst and how they work

catalyst in same phase as the reactants

reaction proceeds through intermediate species