Past Exam Questions Flashcards
Why are iron tablets sometimes medically prescribed?
To treat anaemia - iron is needed to form haemoglobin in red blood cells
Why must potassium manganate (VII) solutions be standardised?
Potassium permanganate/potassium manganate (VII) solutions must be standardised as potassium permanganate is not a primary standard
Why was it necessary to standardise the potassium manganate (VII) solution immediately before use in the titration?
It must be standardised immediately before use in the titration because the solution is unstable - it decomposes in presence of sunlight
What reagent is used to standardise the potassium manganate (VII) solution?
Ammonium iron (II) sulfate is used to standardise the potassium permanganate
Describe how exactly 250 cm cubed of Fe2+ solution was prepared from five iron tablets, each of mass 0.325g.
(9)
Grind up the tablets using a pestle and mortar
Add dilute sulfuric acid to the mortar and wash the contents into a beaker of dilute sulfuric acid
Stir the solution to dissolve the tablets
Using a funnel and glass rod, transfer the solution to the volumetric flask
Transfer all the washings from the beaker to the volumetric flask
Make sure that the flask is on a level surface and that your eye is level with the mark on the volumetric flask
Bring the bottom of the meniscus up to the mark with deionised water
When bringing the meniscus up to the mark, add the water drop by drop
Invert the stoppered flask about twenty times
Why was some dilute sulfuric acid used in making up this solution?
The sulfuric acid is added as it prevents the Fe2+ ions being oxidised to Fe3+ ions by oxygen in the air or oxygen dissolved in the water (or it prevents hydrolysis)
Explain why additional dilute sulfuric acid must be added to the titration flask before each titration is carried out.
Additional sulfuric acid must be added to the titration flask before each titration in order to ensure complete conversion of MnO4- to Mn2+ thereby preventing the formation of MnO2
What is the reducing agent in this reaction?
Fe2+
What is the oxidising agent in this reaction?
MnO4-
