Redox Titrations Flashcards

1- filling the burette with the potassium managanate vii solution.
fill KMnO4 in burette, fill above 0 cm mark first reading @ eyelevel.
UNTIL TOP OF MENISCUS ON 0CM MARK

Dilute sulfuric acid (H2SO4) is added to the deionised water when making up the solution of hydrated amonium sulfate.

BEFORE TITRATION BEGINS, EXCESS DILUTE SULFURIC ACID H2SO4 IS ADDED TO THE HYDRATED AMMONIUM IRON II SULFATE IN THE CONICAL FLASK
the purple drops will decolourise during the titration, at the end point a permanent pink colour is observed in the conical flask.

no indicator required, potassium manganate acts as its own indicator (self indicating)

during the titration- the potassium mananate is added to the acidified hydrated ammonium iron II sulfate, its purple colour decolourises
at end point- a permanent pink colour is observed in the conical flask

during titration- Mn 7+ ions cause the purple colour in KMnO4.
Fe2+ ions are oxidised to Fe3+ ions : the Mn7+ ions are reduced to Mn 2+ ions
as Mn2+ ions are formed the purple colour decolourises

at end point- There is no more Fe2+ ions to reduce the MN7+ ions The last drop of KmnO4 is added and leaves a permanent pink colour.

Potassium manganate VII is not a primary standard,it cannot be obtained in a pure state

Hydrated ammonium iron ii sulfate is a primary standard, it can be obtained in a pure form that is stable in air and can be dissolved in water to make up a solution of accurately known conc.

Iron ii sulfate is easily oxidised by oxgen in the air, not a suitable primary standard
Ammonium II sulfate can be obtained in a pure state that is stable in air and has a high mm and can be dissolved directly in water to make a solution of known conc

Mn2+ ions act as a auto catalyst, as more are formed they speed up thye reaction and cause the purple colour to decolourise more rapidly.- auto catalysis

1- sulfuric acid is added when making up and dissolving the hydrated ammonium iron II sullfate into solution- Prevent Fe2+ ions being oxidised to Fe3+ ions by oxygen in the air

2- excess sulfuric is added to the hydrated ammonium II sulfate solution in the conical flask before titrating against potassium manganate VII - only in an acidic enviorment are MN 7+ ions reduced to Mn2+ ions and NOT Mn 4+ ions

not enough dilute sulfuric acid has been added to the hydrated ammonium iron II sulfate before the titration_ Mn+7 ions have ONLY been reduced to Mn+4 ions and an insoluble brown percipitate has been formed

The potassium permanganate is read from the top of the meniscus eye level .
The intense purple colour of potassium manganate (VII) makes it difficult to read from the bottom of the meniscus.
(Also for this reason, dilute solutions of potassium manganate (VII) are used)

1 fill burette with standard solution of potassium manganate VII. Read from top of meniscus at eye level
2. making the iron tables up into solution. The iron tablets need to be crushed with a pestle and mortar and dilute sulfuric acid is added to the deionied water when making up the iron tablet solution.

before titration begins, excess dilute sulfuric acid is added to the iron tablet solution in the conical flask.
the purple KMnO4 decolourises and a permant pink colour forms.

Iron (II) sulfate

Iron is part of haemoglobin in our red blood cells which carry oxugen and provide energy. A person suffering from anameia may be perscribes iron tablets for tirednedd and fatigue

KMnO4 perviously titred against a standard sln of Hydrated ammonium iron II sulfate

1- sulfuric acid is added when making up and dissolving the grounded iron tablets into solution- Prevent Fe2+ ions being oxidised to Fe3+ ions by oxygen in the air

2- excess sulfuric is added to the iron tablets solution in the conical flask before titrating against potassium manganate VII - only in an acidic enviorment are MN 7+ ions reduced to Mn2+ ions and NOT Mn 4+ ions

KMnO4 is unstable, it decoposes in the presence of light and heat

Procedure: making the dosium thiosulfate up into a solution if required.

2: filling te burette with the sodium thisulfate solution.

3. making a standard soultion of iodine using potassium permanganate - irodine is not a primary standard.

A set volume of perviously standardised solution of potassium maganate is reacted with EXCESS potassium iodide (KI) and EXCESS sulfuric acid (H2SO4) to form iodine.

The colour change at THIS point is purple to red-brown. (2:5) ratio.

Carry out titration, Colour change during titration. goes from red-brown colour to yellow to pale yellow. When pale yellow, add starch solution indicator. The solution in conical flask turns blue- black. At the end point all iodine is used up and solutio becomes colourless.

startch solution is added when close to the end point of a titration, when a pale yellow colour forms

starch is biodegradable

red-brown to yellow to pale yellow. Now add starch - a blue black colour forms. Blue-black to colourless

During the titration the sodium thosufate is added to and reacts with the iodine, whos colour becomes less intense as its being used up in the reaction.

At the end point starch solution indicator is added and a blue black colour forms due to small amount of iodine left, as soon iodine has been conpeltely used up the blue-black colour decolourises.

1) waiting until pale yellow colour tells us end point is very near.the sodium thiosulfate can be added in slowly in small drops, resulting in accurate end point

2) Iodine absorbs onto starch, preventing it reactig with sodium thiosulfate, adding too early results in innacuratly large end pt

sodium thiosulfate is not a primary standard- it is a hydrated compound and loses some of their water of crystallisation in dry air- cannot be obtained in a pure state, so a percise mass cannot be weighed out

iodine is not a primary standard

Iodine sublimes (changes directly drom a solid to a vapour at room temperatire)

poorly soluble in water

reacted with excess potassium iodide and excess sulfuric acid (it has molar ratio 2:5)

Colour change is purple to red brown.

Only in an acidic enviorment are Mn7+ ions fully reduced to Mn2+ ion, meaning that the I- ions will be fully oxidised to form iodine Produces the max amount of iodine

nitric acid is an oxidising agent- will interfere

Hydrocloric acid will be oxidised by potassium manganate forming Cl2

1- potassium iodide in excess ensure that the potassium manganate is the limiting reagent- ensuring all of the potassium mangante reacts- produces max amount of iodine

2- the iodine that is produced will react with potassium iodine in excess forming the triiodide ion I3- a soluble version iodine- keeps iodine in aqueous solution.

reacting the acdified potassium manganate with EXCESS potassium iodine. The iodine that is produced will react with the potassium iodide in excess forming the triiodide ion I3-. keeps iodine in aqeous solution

1.making the sodium thiosulfate up into a standard solution (if required)

2.Filling the burette with the sodium thosulfate solution.

diluting the bleach

4.making a solution of iodine using the diltued bleach- a set volume of the diluted bleach containing sodium hypochloride (NaCLO) is pipetted to a conical flask and reacted excess potassium (KI) and excess sulfuric acid (H2SO4) The colour wil change from colourless to red-brown, the molar ratio means the moles of sodium hypocloride can be known.

The titration is carried out red-brown to yellow to pale yellow. Starch indicator is added, solution turns blue black, at ent point, titration, solution becomes colourless.

3-10%

the sodium thisolfate was previously standardised by titration it against a standard solution of iodine

the orginal bleach was too concentrated meaming the end point of the titration would take too long to occour. a large volume of sodium thiosulfate would be required.

the diluted bleach containing sodium hypochlorite is reacted with excess potasium iodide and excess sulfuric acid

colourless to red-brown

Only in an acidic enviorment are CLO- ions in sodium hypochlorite fully reduced to Cl- ion. I- ions will be fully oxidised to form iodine (i2) produces the maxium amount of iodine

1.Potassium iodide in excess ensures that the sodiim hypochlorite is the limiting reagent - the ensures all of the sodium hypochlorite reacts- produces max iodine.

The iodine that is produces will react with the extra potassium iodide in excess forming the triiodine ion I3- keeps iodine in aqueous solution

Study These Flashcards

reacting the acidified sodium hypochlorite with excess potassium iodide. The iodine that is produces will react with the potassium iodide in excess forming the triiiodide ion I3-

Deionised water has all ions removed but could still contain chlorine- chlorine is an deoxidising agent.

Distilled water is the most pure form of water