Oxidation And Reduction Experiments

Question 1

How can 25cm of bleach solution be diluted

Answer 1

1) Use funnel to transfer original bleach to correctly prepared 500cm3 conical flask
2) rinse beaker funnel and glass rod into volumetric flask with deionised water
3) fill to 500cm3 with bottom of meniscus on mark with deionised water
4) stopper and invert several times

Question 2

Why must excess Kl be added to the diluted bleach

Answer 2

To ensure all hypochlorite reacts

Question 3

State the colour change in the first reaction (bleach experiment)

Answer 3

Colourless to brown

Question 4

Identify a indicator for titration and describe the end colour change (bleach)

Answer 4

Starch solution

Pale yellow to blue to colourless

Question 5

Explain standard solution

Answer 5

Solution of known concentration

Question 6

Give two properties if a primary standard

Answer 6

Pure, solid

Question 7

Why is it necessary to use dilute sulphuric acid

Answer 7

To stabilise fe2+

Question 8

Why is it necessary to add more dilute sulphuric acid to each 25cm portion

Answer 8

To prevent formation of Mn02 brown ppt

Question 9

Describe end procedure of titrations and what observation indicates correct end point

Answer 9

Swirl flask while adding manganate

Read burrette at eye level
Keep burette vertical
Read top of meniscus
Carry out a rough titration

Faint Pink colour remains

Question 10

Why why just potassium mangante solutions be standardised? Why was it necessary to standardise it immediately after titration? What reagent is used for this purpose?

Answer 10

Not primary standard
Unstable
Ammonium iron (II) sulfate

Question 11

Describe how 250cm3 of iron tablet solution was prepared

Why was some dilute Sulfuric acid used in making up solution

Answer 11

Tablets crushed and dissolved
Transferred with rinsing to 250cm3 volumetric flask
Bottom of meniscus on mark

Prevents oxidation by air of iron (II)

Question 12

Why was additional dilute sulfuric acid added before each titration

Answer 12

To ensure complete conversion of MnO4- to Mn2+

To prevent formation of brown ppt

Question 13

How is iodine brought into aqueous solution

Answer 13

Reaction with iodide

Question 14

Describe procedure for measuring 25cm of iodine solution into a flask

Answer 14

Pour iodine into a clean dry beaker

Use pipette that was previously rinsed with deionised water

Question 15

At what stage is starch added to iodine

Answer 15

When colour in conical flask is pale yellow

Question 16

State colour change at end point in presence of indicator

Answer 16

Blue black to colourless

Question 17

Why would you use distilled instead of deionised

Answer 17

Deionised water has had only ions removed

Question 18

What is a primary standard

Answer 18

A pure stable substance of which solution of known concentrations can be made

Question 19

Describe how crystalline thiosulfate was dissolved

Answer 19

Rinse from clock glass into beaker containing ionised water
Stir
Dissolve
Pour through funnel into vol flask
Add rinsings of beaker

Question 20

What must be added to being iodine into aqueous solution

Answer 20

Source of iodide ions

Question 21

Give the colour change in iodine experiment

Answer 21

Brown to yellow to blue black to colourless

Question 22

What colour developed when potassium iodide and sulfúric acid reacted witch bleach

Answer 22

Brown

Question 23

Why was excess potassium iodide used in experiment

Answer 23

So that all bleach has reacted to keep iodine in solution

Question 24

What was purpose conical flask on white tile during titrations

Answer 24

So colour change clearer

Question 25

Name the indicator used in titrations at state colour change

Answer 25

Starch

Blue to colourless