Mandatory Student Experiment No. 10

Question 1

Why are iron tablets sometimes medically prescribed?

Answer 1

To prevent anaemia

Question 2

Why must potassium manganate (VII) solutions be standardised?

Answer 2

As they are not a primary standard

To find their concentration

Question 3

Why was it necessary to standardise the potassium manganate (VII) solution immediately before use in the titration?

Answer 3

It would have begun to decompose

Question 4

What reagent is used to standardise potassium manganate (VII)?

Answer 4

Ammonium iron (II) sulfate

Question 5

Describe how exactly 250cm cubed of Fe2+ solution was prepared from five iron tablets, each of mass 0.325g.
(7 points)

Answer 5

Tablets were crushed with mortar and pestle
Crushed tablets were washed into beaker
Crushed tablets were combined with dilute sulfuric acid
Solution is transferred with rinsings to a 250cm volumetric flask
The bottom of the meniscus of the solution is brought up to the mark with deionised water
Flask is read from on a level surface and from eye level
Invert the volumetric flask

Question 6

Why was some dilute sulfuric acid used in making up this solution?

Answer 6

Prevents oxidation by air of iron (II)

Question 7

Explain why additional dilute sulfuric acid must be added to the titration flask before each titration is carried out

Answer 7

To ensure complete reduction of MnO4- to Mn2+

Prevents the formation of Mn4+

Question 8

How was the end-point detected?

Answer 8

A pale pink colour remained