Chem Practical (volumetric Analysis)

Question 1

Why starch is added only when the soln turns pale yellow

Answer 1

If u do, then more iodine molecules will be strongly absorbed on the starch molecules to form the blue-black complex. As release of iodine molecules from the complex to react with S2O3 2- takes time, this causes the colour change to occur less readily and reduces the accuracy of the titration

Question 2

Why not force out the last drop in the pipette

Answer 2

Cuz it is calibrated during manufacture. Doing so will result in more soln than required

Question 3

Burette reading to what dp

Answer 3

2dp

Question 4

Why need continuous swirling

Answer 4

To ensure even mixing

Question 5

Pipette vol to what dp

Answer 5

1 dp

Question 6

Electronic Balance dp

Answer 6

Write everything so 3dp

Question 7

Purpose of draught protection shields

Answer 7

Ensure reading is not affected by wind or movement

Question 8

If u were given a empty bottle to find mass how to present?

Answer 8

Mass of FA1 + weighing bottle/g
Mass of empty weighing bottle/g
Mass of FA1/g

Question 9

If u were given bottle with mass already inside, how to present

Answer 9

Mass of weighing bottle + FA1/g
Mass of weighing bottle + residual/g
Mass of FA1/g

Question 10

Possible reasons for anomalous results

Answer 10

1. The titrant was not added drop wise near the end point, making it difficult to know endpoint
2. Soln in conical flask was not swirled continuously to ensure complete mixing
3. The standard soln prepared was not mixed thoroughly to ensure Homogenous mixture