23.2 manganese (VII) redox titrations Flashcards
The titration of Manganate (VII) doent need an indicator beacause
it is self indicating. Colourless (Mn2+) - permanent pink (indicating small excess of Mn04- ions)
Manganate (VII) is reduced by …. supplied by the addition of ….
H+ ions supplied by the addition of excess dilute H2SO4
Slight differnece to normal titration
when dealing with ….. we don’t read the miniscus from the bottom
KMnO4 (deep purple colour)
instead we read from the top beacuse very dificult to see the meniscus throught the intense colour
another name for
potassium manganate (VII)
potassium permanganate
what is the formula for
percentage purity
mass of x that reacted/ mass of sample used x100
The following half equation represents the oxidation of hydrogen
peroxide when hydrogen peroxide is acting as a reducing agent.
Equation: H2O2(aq) → O2(g) + 2H+(aq) + 2e-
The reduction of hydrogen peroxide when hydrogen peroxide is acting as
an oxidising agent in acidic conditions.
In acidic solution: H2O2(aq) + 2H+(aq) + 2e- → 2H2O(l)
The reduction of hydrogen peroxide when hydrogen peroxide is acting as
an oxidising agent in alkaline conditions. This reaction is less common
but is sometimes seen after ligand substitution reactions with aqueous
ammonia (ammonium hydroxide).
In alkaline solution: H2O2(aq) + 2e- → 2OH-(aq)
A disproportionation reaction occurs with hydrogen peroxide where the oxygen is
simultaneously oxidised and reduced. This DOES NOT happen in redox titrations.
Equation: 2H2O2(aq) → O2(g) + 2H2O(l)
Redox titrations are carried out in a similar way to acid-base titrations but in redox
titrations an …… agent is titrated against a ……. agent.
oxidising agent is titrated against a reducing agent.
Redox vs acid-base titrations
Redox titrations
- Don’t need an indicator (self-indicating, due to nice colours of transition elements!)
- Have an oxidising agent and a substance that is going to be oxidised (find out amount of substance oxidised)
- Work out conc. of oxidising agent
- MORE COMPLEX CALCULATIONS!
Acid-base titration
- Determines unknown conc. of acid/ base
- Requires a suitable indicator to observe end point
- Relatively straight forward calculation
HCl can not be used as it reacts with KMnO4.
Hydrochloric acid (HCl) cannot be used in potassium permanganate (KMnO4) because it reacts with KMnO4 and is oxidized to produce chlorine gas, which makes the solution less acidic
using K2Cr2O7 as an oxidising agent is self indicationg from … … ions to …… …. ions
orange Cr2O7 2-
Cr3+ green
What ions does Zn form?
Zn 2+ only
reduction of Cr2O7 2-
Cr 3+
