16B.2 Flashcards
what is potassium manganate
it is KmnO4 and it is a powerful oxidizing agent
what is potassium manganate used in
it is used for the quantitate estimation of many reducing agents, especially compounds of iron(II) and for ethanedioic acid and its salts
in acidic solution what is the half-equation for the reduction of manganate(VII) ions
MnO4(aq) + 8H(aq) + 5e- —–> Mn^2+(aq) + 4H2O(l)
in redox titrations why is KMnO4 used only in a acidic solutions
because in alkaline solutions the KMnO4 can yield Manganese (IV) oxide as a brown precipitate which then interferes with the end point colour
how does KMno4 act as its own indicator in redox titrations
at the beginning the purple colour KMnO4 started reacting with the acidic titrate to form Mn^2+, so as titration proceeds, manganese(II) ions, Mg^2+, accumulate but, at the dilution used, they give a colourless solution, so as soon as KMnO4 is in excess they give a pink colour, so therefore the end point is reached
what are the two half equation and full equation involved in the redox titration of Iron(II) ions and KMnO4
page 174
what is the colour of MnO4 ^-
purple (Potassium manganese (VII)
what is the colour of Fe^2+(aq)
pale green
what is the colour of Fe^3+(aq)
yellow
what is the colour of Mn^2+(aq)
pale pink
why do some ions in titrations appear colourless
because they are diluted
what is the method of titration used for KMnO4 and iron(II)
- pipette an accurately measured volume of iron(II), usually 25cm^3, into a conical flask and then add a small volume of dilute sulfuric acid
- slowly add KMnO4 solution of a known concentration from a burette and swirl the mixture
- The KMnO4 solution will turn colourless until all of the iron(II) ions are fully oxidized
- the addition of one drop of KMnO4 will cause the solution to turn pale pink
why cant acidified Potassium dichromate be sued as an oxidizing agent for quantitative redox titrations
since the change between orange and green has no clear end point
what is the ionic half equation pf ethanedioic acid
H2C2O4(aq) —-> 2H+(aq) + 2CO2(g) + 2e-
what is the overall equation between KMno4 and ethanedioic acid
Page 175
what is the method used for redox titration of KMnO4 and ethadoic acid
- Aq ethanadioic is pitted into a conical flask, usually about a volume of 25 cm^3, and then it is acidified by dilute sulfuric acid (note: ethanadioic acid is extremely poisonous so a pipette filler must be used)
- the reaction is very slow so heat the acid to about 60c
- slowly add KMnO4 solution of a known concentration from a burette and swirl the mixture
- The KMnO4 solution will turn colourless until all of the acid is reduced (it will turn colourless only once Mn^2+ ions form and start catalyzing the reaction, because before the first sample is added the reaction will be very slow and the pink colour wont immediately disappear)
- The addition of one drop of KMnO4 will cause the solution to turn pale pink
why is Sulfuric acid boiled
it is boiled to remove any dissolved oxygen that might otherwise oxidize some species
What is the procedure for the redox titration between hydrated iron(II) sulfate crystals and potassium manganate(VII)
- bring to boil 100cm^3 of sulfuric acid and then allow it to cool to room temperature
- weigh accurately a weighing bottle containing 7g of hydrated iron sulfate crystals
- Dissolve the crystals in the cool acid and reweigh the bottle. transfer the solution into a 250 cm^3 volumetric flask. ass several washing to the beaker and make up to the mark. shake well
- titrate a 25 cm^3 sample of iron(II) solution with standard KMnO4
5.preform repeat Titrations until you obtain concordant results
what are the safety note for redox titration between hydrated iron(II) sulfate crystals and potassium manganate(VII)
wear eye protection, avoid skin contact. make sure the top of the burette isn’t at eye level when you fill it
what are the half equations and the full equation for the redox titration between Iodine and sodium thiosulfate
page 176
what indicator is used in the redox titration between Iodine and sodium thiosulfate
starch solution, as in the presence of iodine it produces a blue-black colour, so when a sufficient amount of sodium thiosulfate is added to react with the iodine the colour disappears
what is the procedure of the redox titration between Iodine and sodium thiosulfate
- add sodium thiosulfate from a burette into a iodine solution, until the original brown colour of iodine changes to pale yellow 2. add a few drops of starch solution to produce the blue colouration
- add sodium thiosulfate solution drop by drop until the blue-black colour turns colourless
why isn’t starch solution added from the beginning of the redox titration between Iodine and sodium thiosulfate
some of the starch solution would react absorb the iodine reducing the accuracy of titration
if their is a colour change with the redox titration between Iodine and sodium thiosulfate why is starch needed
because it would be very difficult to detect the end point, as the colour of the iodine solution becomes very faint towards the end of the titration
what is the procedure used for the redox titration between Iodine (that comes from copper(II) sulfate crystals) and sodium thiosulfate
- weigh accurately a weighing bottle containing 6g of hydrated copper(II) sulfate crystals
2.tansfer the crystals into a 250 cm^3 volumetric flask and reweigh the bottle
- add sodium carbonate until a slight permeant blueish precipitate of copper(II) carbonate forms
- acidify the solution with dilute ethanoic acid until a clear blue solution forms (Copper(II)). Make up the solution to 250cm^3 with denoised or distilled water and shake well
- pipette 25 cm^3 into a conical flask and add about 1.5 grams of potassium iodine
- Titrate the Iodine produced with sodium thiosulfate, adding starch solution when the mixture becomes pale yellow
what is the procedure used for the redox titration between Iodine (that comes from copper(II) sulfate crystals) and sodium thiosulfate
- weigh accurately a weighing bottle containing 6g of hydrated copper(II) sulfate crystals
2.tansfer the crystals into a 250 cm^3 volumetric flask and reweigh the bottle
- add sodium carbonate until a slight permeant blueish precipitate of copper(II) carbonate forms
- acidify the solution with dilute ethanoic acid until a clear blue solution forms (Copper(II)). Make up the solution to 250cm^3 with denoised or distilled water and shake well
- pipette 25 cm^3 into a conical flask and add about 1.5 grams of potassium iodine
- Titrate the Iodine produced with sodium thiosulfate, adding starch solution when the mixture becomes pale yellow. the end point titration is achieved once you can see a white suspension of insoluble CuI in a colourless solution
- preform repeat titrations until you achieve concordant results
what is the reaction between Cu^2+ and potassium Iodine in the redox titration between Iodine and sodium thiosulfate
2Cu^2+ (aq) + 4I^-(aq) —-> 2CuI(s) + I2(aq)
why must the cupper(II) sulfate used in redox titration between Iodine and sodium thiosulfate free from anything but a trace of mineral acid
because then the end point wont be accurate
