A2 redox Flashcards
Define oxidising agent
Takes electrons from the species being oxidised (is reduced)
Define reducing agent
Adds electrons to the species being reduced (is oxidised)
Manganate (VII) Redox titration procedure
1) Add standard solution of KMnO4 to a burette
2) Using a pipette, add a measured volume of solution to a conical flask
3) Add dilute excess sulfuric acid (H+ ions will reduce MnO4)
4) End point = first permanent pink colour (excess of MnO4- ions)
5) repeat until concordant, read from the top of the meniscus as it is too dark
How to calculate the percentage purity of an iron (II) compound from a MnO4- titration
1) Calculate the moles of MnO4- that reacted
2) Use the equation ratio (1:5 in this case) to work out moles of Fe
3) Scale up to original amount
4) x Mr = mass
5) mass percentage
Analysing % purity of an iron (II) compound - procedure
1) 250cm3 solution of impure FeSO4.7H20 in a volumetric flask
2) Use a pipette to get 25cm3 into a conical flask
3) Using a burette, titrate using 0.2moldm-3 KMnO4(aq)
Manganate and Iron reduction equation
MnO4-(aq) + 8H+(aq) + 5e- —> Mn2+(aq) +4H20(l)
Manganate and Iron oxidation reaction
Fe2+(aq) —> Fe3+(aq) + e-
Manganate and Iron overall equation
MnO4-(aq) + 8H+(aq) + 5Fe2+(aq) –> Mn2+(aq) + 5Fe3+(aq) +4H2O(l)
What are iodine/thiosulphate titrations used for?
To determine the The ClO- content in bleach, or the Cu2+ content in copper (II) alloys
Equations for Copper and iodine
2Cu2+ +4I- –> “CuI +i2
The iodine produced in equation one is then titrated with a known solution of sodium thiosulfate :
S2O3 2- + I2 –> 2I- + S4O6 2-
Procedure for an iodine/ thiosulfate titration
1) Add standard solution of Na2S2O3 to a burette
2) Prep the solution of oxidising agent and add to a conical flask with a pipette
3) Add an excess of potassium iodine (the oxidising agent will react with the iodide ions to produce iodine, making it go brown)
4) Titrate with Na2S2O3, when it turns a pale straw colour, add starch solution and wait until decolourises
