chem : titrations

burette

used to measure amount of liquid added to comical flask

how to use a burette

1. always rinse out burette before use with deionised water

2. then rinse it with solution its going to contain to was out deionised water

3. clamp it veritacly

4. fill it using funel then remove the funnel

5. read from teh botton of teh meniscus, at eye level, except for KMnO4-, read from top

6. remove air buble from jet by opening tip quickly

7. add solutin from burette drop-wise when near end point

pipette

gives an absolute precise volume of liquid

how to use pipette

1. rinse with deionised water

2. rinse with solution its going to contain

3. fill it using pipette filter, as solution may be poisonous

4. empty it into conical flask and touch teh tip against teh side of the flask

5. dont blow out the drop left at the bottom of pipette as it was already accounted for when it was calibrated

teat pipette

used for adding drops when not worried about volume, i.e adding indicator

how to use conical flask

1. rinse it with deionised water only

2. place on white surface

3. add indicator using teeth pipette, add only a few drops of indicator as too much may change teh result

4. mix it continousely by stirring

5. allow time between each drop to allow time for reaction to occur

6. wash down drops onto side of flask using deionised water

indicators

tells us when a recation is complete by changing colour, should change colour at a ph where ph changes arpidly in a reaction

end point

point at which indicator colour changes

SAWB

methynl orange

SASB

any

WASB

phenolphthalein

SA

HCl

WA

CH3COOH

SB

NaOH

WB

Na2CO3

indicator colours

1. methynl orange, red, yellow

2. litmus, red, blue

3. phenophthalein, colourless, purple

permanganate (MnO4-)

• used in determinig amount of iron in ireon tablets EXP

• first lot of Dil. H2SO4 needs to be added to prevent atmospheric oxygen from oxidising Fe2+ to Fe3+

• second lot of Dil. H2SO4 needs to be added or brown percipitate is formed of MnO4-

• acts as own indicator

• end point = solution is permenantly purple

starch

• iodine - thiosulphate tittrations

• add when solution is straw coloured

• goes blue when added

• turn colourless at end point

eriochrome black (T) or solochrome black

• used in EDTA titrations

• buffer solution must be added to ensure ph > 10 so indicator works properly

• goes from wine red to blue at end point

standard solution

solution whose concentration is known acurately

primary standard

solution that can be made up directly of pure, stable solid

to be a primary solution a substance must be:

1. pure

2. stable

3. solid

4. high molecular mass

5. very soluble

eg of primary standard solution

anhydrous Na2CO2 (soduim carbonate) and amonium iron (II) sulphate (Mohr’s salt)

preparing standard solution

1. weigh out accurate mass of compund on a closk glass

2. wash clock glasss into beaker of deionised water

3. stir well to desolve

4. rinse strring rod into beaker using deionised water

5. pour into volumetric flask usinf funnel

6. rinse beaker into volumetric flask

7. add deionised water drop-wise to raise the meniscus to teh calibration mark

8. invert repitadly to mix

secondary standard solution

make a solution tehn standardise it using primary standard

standardise

to find the concentration of a solution to find titration

substances that acnt be used for primary standardisation and why

1. MnO4-, isnt pure

2. iodine (I2), it sublimes

3. NaOH or KOH, absorbs moisture and CO2 from atmosphere

substances used to standardise and what they standardise

1. anhydrous sodium carbonate to standardise HCl

2. anhydrous amonium iron (II) sulphate to standardise MnO4-

volumetric flask

1. rinse with deionised water only

2. read from bottom of meniscus at eye level

3. add deionised water drop wise when near calibration mark

4. mix by inverting 10 times to make sure the solution is homogeneous

preparing a titration

1. correct indicator

2. only use 3-4 drops of indicator

3. do 1 rough titration and 2 accurate titres

4. average the 2 accurate titres

5. mix contents well by swirling

6. add from buette drop wise near the end point

titration : find concentration of ethonic acid in vinegar

• dilute vinegar, because acid is too concentrated

• use NaOH (strong base), ethanoic acid is a weak acid

• indicator - phenophthalein, pink in alkaline, colourless in acid

• multiply answer of concentration by dilution factor

titration : iodine/ thiosulfate

• idoine solution is brown (standard solution)

• not very solublein water so Ki- is added to help it dissolve

• indicator - startch, goes blue black when iodine is present

• add indicator when solution is straw coloured, or else it will complex with teh iodine and ruin teh results

• end point is when solution becomes colourless, when no iodine is left

estimate %(w/v) hypochlorite in bleach

• CIo in bleach provides free chlorine, chlorine that is available as an oxidising agent

• dilute, bleach conc is too strong

• add Dil sulphuric acid to ensure reaction goes to completion

• add 0.5M KI- (excess0:
  forms iodine
  helps iodine dissolve in the water

wrinkler method to determine the dissolved oxygen in water

1. wet bottle to prevent air from sticking to the side of the bottle

2. fill the stopper underwater to ensure nobubbles

3. add conc. MnSO4 and alkaline KI (KOH + KI) using droppers under water to prevent reaction with O2 in the air

4. small amounts of conc solution are used as not to change volume of sample significantly

5. put stopper back on without trapping air bubbles

6. invert a number of times

7. f white percipitate does not become brown it means there is dissolved oxygen in teh water

8. add conc H2SO4 carefully down teh side of the bottle

9. brown percipitate dissolves as it forms iodine

10. standardies using iodine (thiosulphate) solution

hard water

water hat forms scum with soap

meaasured in CaCO3

temporary hardness of water

removed by boiling

caused by Ca(CHO3)2

causes of permanent hardenss of water

MgCl2,CaCl2, MgSO4, CaSO4

determine hardness of water

indicator - eriochrome black

colour change - wine red to blue

buffer solution to keep >10 ph so indicator works

unboiled water = temp. permanent

boiled = permanent only

add buffer solution to conical flask

add indicator - wine red

add EDTA

end point = solution turns blue

EDTA

Ethylene Diamine Tetra Acetic acid

determine the degree of hydration of sodium carbonate

indicator - methynal orange

HCl in burrete

NA2CO3 in flask

end point is when solution goes from orange to pink

weigh out accurate mass of hydrated sodium carbonated crystals

dissolve crystals in deionised water

make up to calibration mark in volumetric flask, invert multiple ties to make solution homogenous

take out some of the solution using pipette into the conical flask