Mandatory Student Experiment No. 9

Question 1

Explain what is meant by a standard solution

Answer 1

A solution whose concentration is accurately known

Question 2

Give two essential properties of a primary standard for volumetric analysis

Answer 2

Must dissolve easily in water

It must be anhydrous

Question 3

Why is it necessary to use dilute sulfuric acid when preparing the standard solution from hydrated ammonium iron (II) sulfate?

Answer 3

To avoid formation of Fe3+

Question 4

Why is it necessary to add more dilute sulfuric acid to each 25.0 cm cubed portion of the standard solution used in the titrations?
(2 reasons)

Answer 4

To prevent the formation of MnO2 which is brown

To ensure MnO4- reduces to Mn2+ which is colourless

Question 5

Describe fully the procedure used during the titrations to ensure accuracy of the end point
(5 points)

Answer 5

Swirl conical flask while adding manganate(VII) solution from burette
Add manganate(VII) slowly/drop by drop from the burette as end point is approached
Read burette from top of meniscus
Carry out a rough titration
Use a white tile to see colour changes in flask clearly

Question 6

What observation indicates that the correct end point has been reached?

Answer 6

Pale pink colour