Background of Titration Experiments(Complete)

Question 1

How do you prepare a burette?

Answer 1

Rinse with deionised water.
Then rinse with the solution that it is going to contain.
Clamp it vertically.
Fill using a funnel and then remove the funnel- drops may fall into the liquid and give a false reading.
Remove air bubbles from the jet by opening the tap quickly.
Read from the bottom of the meniscus-eye level with the point.

Question 2

How do you prepare a pipette?

Answer 2

Rinse with deionised water.
Then rinse with the solution it is going to contain.
Fill using a pipette filler as the solution may be poisonous or caustic.
Read from the bottom of the meniscus.
Empty into conical flask and touch the tip against the side of the flask.
Do not blow.

Question 3

How do you prepare a conical flask?

Answer 3

Rinse out with deionised water only.
Place on a white tile to see the colour change more easily.
Mix continuously by swirling the contents.
Add only a few drops of indicator as they are weak acids and bases and may upset the results.
Wash down drops on the side of the flask with deionised water.

Question 4

How do you prepare a volumetric flask?

Answer 4

Rinse with deionised water only.
The long thin neck makes it more accurate.
Read from the bottom of the meniscus at eye level.
Add deionised water dropwise when near the calibration mark.
Mix by inverting ten times to make sure that the solution is homogeneous. (long thin neck makes this necessary)

Question 5

How do you prepare a titration?

Answer 5

Use the correct indicator.
Only use 3-4 drops of the indicator.
Mix well by swirling.
Add from burette drop wise near the end point.
Do one rough and 2 accurate titres.
The accurate titres should agree within 0.1cm3.

Question 6

What is an indicator?

Answer 6

A substance that changes colour with pH or at the end-point of a titration.

Question 7

Name the indicators?

Answer 7

Phenolphthalein.
Methyl Orange.
Litmus.
Starch.
MnO4-.
Eriochrome Black.

Question 8

What is a strong acid?

Answer 8

Dissociates fully in aqueous solution.

Question 9

What are the strong acids?

Answer 9

HCL- Hydrochloric Acid.
HNO3- Nitric Acid.
H2SO4- Sulfuric Acid.

Question 10

What is a weak acid?

Answer 10

Does not dissociate fully in aqueous solution.

Question 11

What are the weak acids?

Answer 11

CH3COOH- Ethanoic Acid.

HCN- Hydrogen Cyanide.

Question 12

What is a strong base?

Answer 12

Dissociates fully in aqueous solution.

Question 13

What are the strong bases?

Answer 13

NaOH- Sodium Hydroxide.

KOH- Potassium Hydroxide.

Question 14

What is a weak base?

Answer 14

Does not disassociate fully in aqueous solution.

Question 15

What are the weak bases?

Answer 15

Na2CO3- Sodium Carbonate.

NH4OH- Ammonium Hydroxide.

Question 16

What indicator is used for a strong acid with a strong base?

Answer 16

Any indicator.

Question 17

What indicator is used for a strong acid with a weak base?

Answer 17

Methyl Orange.

Question 18

What indicator is used for a weak acid and a strong base?

Answer 18

Phenolphthalein.

Question 19

What indicator is used for a weak acid with a weak base?

Answer 19

none

Question 20

When is permanganate used as an indicator ? What is the colour change?

Answer 20

Used in the iron tablet experiment.
Dilute H2SO4 needs to be added or a brown precipitate of MnO2 is formed.
It acts as its own indicator.
Solution becomes permanent pink at the endpoint.

Question 21

When is starch used as an indicator ? What is the colour change?

Answer 21

Used in the iodine thiosulphate titrations.
Add when the solution is straw coloured.
Goes blue when added.
Turns colourless at the endpoint.

Question 22

When is eriochrome black used as an indicator ? What is the colour change?

Answer 22

Used in EDTA titrations.
Buffer solution must be added to ensure the pH > 10 so indicator works properly.
Goes from wine red to blue at the end point.

Question 23

What is a standard solution?

Answer 23

A solution whose concentration we know accurately.

Question 24

What is a primary standard solution?

Answer 24

A primary standard solution is one that can be made up directly using a measured amount of pure solid.

Question 25

To be suitable for use as a primary standard solution, a substance must be:?

Answer 25

Pure.
Stable.
Have a high molecular mass.
Very soluble.

Question 26

How do you prepare a primary standard solution?

Answer 26

Weigh out an accurate mass of sodium carbonate crystals on a clock glass.
Rinse clock glass into a beaker of deionised water.
Stir until fully dissolved.
Pour into a volumetric flask using a funnel.
Rinse the beaker and funnel into the flask with deionised water.
Fill until the bottom of the meniscus is level with the mark.
Place a stopper and invert it ten times to make the solution homogeneous.
The long neck makes it accurate.

Question 27

What does standardise mean?

Answer 27

To find the concentration of a solution using titration.

Question 28

What substances can you not use as a primary standard solution and why?

Answer 28

MnO4-: it cannot go pure.
Iodine(I2): because it sublimes.
NaOH/KOH: they absorb CO2 and moisture from the atmosphere.