Prac Reports: Fertiliser prac, Esterification prac, Saponification prac (1 Viewer)

sneaky pete

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I remember copying the method from that back of the jacaranda card into my prac back.. I lost the prac back but still have the card, so..

  • Dissolve a known weight (1.5g) of soluble fertiliser (e.g Sulfate of Ammonia) in 100mL of hot water
  • Add excess barium chloride solution. Heat to coagulate the white BaSO4 precipitate
  • Filter quantitiatively through a pre-weighed fine sintered glass filter. Wash with hot water to remove any soluble salts
  • Dry in an oven and re-weigh to determine the mass of barium sulfate
Calculation: n(BaSO4) = n(SO4)
since (Ba+2 + SO4-2 -> BaSO4)
  • Convert the mass of BaSO4 to moles (n(BaSO4))
  • Convert the moles of sulfate (n(SO4)) to grams (m = nM)
  • Express this mass as a percentage of the weight of the fertiliser sample.

Notes
  • The accuracy of the result depends on ensuring that all the sulfate ions are precipitated and that no precipitate is lost on transfer
  • The weighed precipitate must be completely dry and free from other salts

Also read Frigid's explanation abotu this experiment here

If noone can help you by tonight on the other two pracs I'll try get a scan or some info of a friend, hope the above helps (i do indy chem too)
 
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inasero

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Dissolve a known weight (1.5g) of soluble fertiliser (e.g Sulfate of Ammonia) in 100mL of hot water
you're better off dissolving in conc. HCl for two reasons:
1. dissolution is more efficient
2. helps to coagulate the fine BaSO4 ppt 2gether, thereby increasing accuracy of experimental results
 

Takuya

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Originally posted by sneaky pete
I remember copying the method from that back of the jacaranda card into my prac back.. I lost the prac back but still have the card, so..

  • Dissolve a known weight (1.5g) of soluble fertiliser (e.g Sulfate of Ammonia) in 100mL of hot water
  • Add excess barium chloride solution. Heat to coagulate the white BaSO4 precipitate
  • Filter quantitiatively through a pre-weighed fine sintered glass filter. Wash with hot water to remove any soluble salts
  • Dry in an oven and re-weigh to determine the mass of barium sulfate
Calculation: n(BaSO4) = n(SO4)
since (Ba+2 + SO4-2 -> BaSO4)
  • Convert the mass of BaSO4 to moles (n(BaSO4))
  • Convert the moles of sulfate (n(SO4)) to grams (m = nM)
  • Express this mass as a percentage of the weight of the fertiliser sample.

Notes
  • The accuracy of the result depends on ensuring that all the sulfate ions are precipitated and that no precipitate is lost on transfer
  • The weighed precipitate must be completely dry and free from other salts

Also read Frigid's explanation abotu this experiment here

If noone can help you by tonight on the other two pracs I'll try get a scan or some info of a friend, hope the above helps (i do indy chem too)
If you can get these it would be great. I know how they work but I'd like to know things such as reflux times, volumes, masses, i.e. evidence that you've actually done the experiment. Thanks!
 

Bannanafish

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but you don't want accuracy :p
cause you need to write about improvements :D
 
N

ND

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Originally posted by inasero
you're better off dissolving in conc. HCl for two reasons:
1. dissolution is more efficient
2. helps to coagulate the fine BaSO4 ppt 2gether, thereby increasing accuracy of experimental results
And also so you don't precipitate out any phosphate when you add the barium.

For the esterification:

15ml propanoic acid
15ml ethanol
10drops conc H2SO4

reflux etc.

add 50ml Na2CO3 (cant remeber concentration but i'll say 1mol)
mix, let out air etc.
add some (a tsp?) CaCl2.
 

abdooooo!!!

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im feeling generals today... since chem is on tommorow.

here's your answers:
5.3.1 Identify data, plan, select equipment and perform a first-hand investigation to prepare an ester using reflux.

Procedure:
About 15mL of 1pentanol (C5H12O) and 15mL of ethanoic acid were added
10 drops of concentrated sulfuric acid
Boiling chips (porous ceramic material) were added
The equipment was heated by a Bunsen burner set on a blue flame for 15 to 20 minutes
The mixture is then separated by adding water (100mL) in a separation funnel
The lower aqueous layer is discarded
Sodium carbonate was added to neutralise excess acid
Two layers again formed and the lower discarded
Sodium carbonate was added again and the procedure repeated
A teaspoon of anhydrous sodium sulfate was added to remove excess water
The ester is then filtered into distillation flask and distilled

Data:
1-pentanol (BP 138oC), ethanoic acid (BP 118oC), 1-pentyl ethanoate (BP 143oC)
1-pentyl ethanoate (density 0.88), water (1.00)
1-pentyl ethanoate (insoluble in water), 1-pentanol (8g/100g in water sparingly soluble), ethanoic acid (miscible in all proportions)

Conclusion:
1pentanol + ethanoic acid → 1-pentyl ethanoate (sulfuric acid as catalyst)

Justification:
Reflux is the process of heating a reaction mixture in a container with a cooling condenser attached vertically
This prevents the escape of volatile reagent and allows reaction to be carried out at a higher temperature than otherwise would
And this also prevents the build up of pressure in the system

Sulfuric acid is used as catalyst to increase the rate of reaction
It also absorbs water, pushing the equilibrium to the right producing more ester

Reactants and products are chosen sufficiently different in boiling point for you to easily separate the ester from the rest of the reaction mixture by fractional distillation

Solubility and density of products and reactant are important for separation

Boiling chips were added to evenly disperse the heat

Sodium carbonate and anhydrous sodium sulfate were added to remove acid and water from the mixture


Safety and Risks:
Corrosive chemicals splashing and spilling
Concentrated sulfuric acid is extremely corrosive
Volatile chemicals are involved
Explosion is fatal

Safe work practice:
Make sure the pipette is not blocked by pieces of cork, otherwise you risk an explosion
Avoid spills of concentrated sulfuric acid
Keep volatile chemicals away from ignition sources
Work near readily supplies of water to wash out fire


3.3.3 Identify data, plan, select equipment and perform a first-hand investigation to measure the sulfate content of lawn fertiliser and explain the chemistry involved.
3.3.4 Analyse information to evaluate the reliability of the results of the above investigation and to propose solutions to problems encountered in the procedure.

Procedure:
A sample of fertiliser containing (NH4)2SO4 was crushed by a mortar and pestle
Weighed to a mass of 10 grams
It was then dissolved in a beaker of warm water
Ba(NO3)2 was added drop-by-drop in excess until no more white precipitate of BaSO4 will form
Precipitate collected by a sintered glass filter
Then dry and weigh the precipitate
The sulfate content was then calculated

Chemistry:
BaSO4 is insoluble in water
(NH4)2SO4(aq) + Ba(NO3)2(aq) → BaSO4(s) + NH4NO3

Reliability problems:
The particles of barium sulfate are very small
The amount of precipitate vary due to temperature
Ions adhere to the precipitate being filtered as well

Reliability solutions:
By controlling the temperature at which the experiment is conducted at, temperature kept at optimum for precipitation of sulfate
Carefully washing the precipitate and drying it to remove ions that adhere to the precipitate
Testing if the supernatant solution still contained sulfate by adding more Ba2+
If more is present add more Ba2+ and filter
Concentrated HCl acid is added to increase the crystal size of the precipitate therefore minimising the lost of sulfate content
A sintered glass filter is used rather than normal filter paper to trap BaSO4 because precipitate crystals are extremely small, this minimises the lost of precipitates

Safety and Risks:
Barium nitrate is a poison. May be fatal if swallowed
Barium sulfate may irritate eyes or act as a respiratory irritant

Safe work practice:
safety glasses
good ventilation
wash hands thoroughly when finished


5.3.1 - perform a first-hand investigation to carry out saponification and test the product.
5.3.4 - perform a first-hand investigation to demonstrate the effect of soap as an emulsifier.

Procedure:
Pour about 30mL of 6 M NaOH solution into a 250mL beaker
Add about 10mL of olive oil to the solution in the beaker
Put a few boling chips in the beaker and gently heat the mixture on an electric hot plate
While stirring, allow the mixture to boil slowly until the olive oil is no longer visible (10-15min)
Allow the mixture to cool for a few minutes before adding 40mL of a saturated solution of sodium chloride (salting out occurs)
Boil the mixture for a further 2-3 min, then cool it in a water bath
Filter the mixture through cotton wool
Wash the residue with water to remove excess NaOH and NaCl
Use a spatula to remove a portion of the collected soap into a large test tube where further tests may be carried out if required
Sample of the crude soap is tested for lathering by shaking with water in stoppered tube

Emulsifier test:
Select a clear glass jar with a lid
The jar should be small but large enough to hold about a half cup of water
Rinse the jar and lid until they are very clean
Partially fill the jar with water, then add a thin layer of cooking oil on top of the water
Cap the jar and shake it well
Set the jar down and let it sit for some time
Now add a drop of liquid soap to the jar
Mix the soap, water, and oil well, but not so vigorously as to foam up the oil surface
Let the mixture sit for some time

Results:
When cooking oil is mixed with water without soap two layers formed, top is the oil bottom water
When soap is added an emulsion formed that looked like milk

Justification:

For Making soap
Boiling chips is added to stop bumping while heating
Saturated sodium chloride is added to salt out (precipitate out) the soap, because soap is soluble in pure water
Cotton wool?
Residue is washed with water because this remove excess NaOH and NaCl
Soap is tested for its lathering properties, because a good soap forms a lather
Electric hot plate is used because it provides a even heating so NaOH solution does not splash

For Emulsifier test
Clear jar is selected to able to see the effect of soap as emulsifier
Jar is rinsed to remove impurities that might hinder soaps emulsifier effect
Oil and water is mixed and shook without adding soap as a control to demonstrate that soap is needed for oil and water to form an emulsifier
When soap is added, the mixture is allowed to sit for some time to demonstrate that an emulsifier has formed and not just temporarily mixed by the shaking


Safety and Risks:
Corrosive chemicals spilling and splashing
Concentrated sodium hydroxide is extremely corrosive
Mixture is heated therefore its very hot and may splash

Safe work practice:
Safety glasses
Gloves
Good ventilation
Avoid spilling of NaOH
Work near readily supplies of water to wash off spills

this is got to be the longest post ever :D
 

monkey289

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for the esterification prac... we used 10 mL 1-pentanol and 12 mL ethanoic acid... y the extra 2 mL?
 

Riviet

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The excess ethanoic acid means that by Le Chatelier's principle, the equilibrium will favour the direction of the reaction that reduces the extra acid, therefore this will shift the equilibrium to the products side, producing more ester and water.
 

hayleynicole4

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Fantastic! :D
But how does the HCl increase the crystal size of the precipitate?

Why is the solution heated, and why is heat important for the precipitate to coagulate?

I have another step in my prac method:
Collect the last drops of filtrate in a 100 mL beaker and test for the presence of chloride ions by adding a few drops of silver nitrate solution to the filtrate. If the solution becomes cloudy, wash the precipitate with a further 10 mL of warm water and repeat the test.
Why would this be important?

Help!!!
 

jasperll

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you're better off dissolving in conc. HCl for two reasons:
1. dissolution is more efficient
2. helps to coagulate the fine BaSO4 ppt 2gether, thereby increasing accuracy of experimental results
Why is the dissolution more efficient?
 

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