CHEMISTRY PAPER 34 (PRACTICALS)

[saudha]

HI
well i couldnt find any thread related to this so i made it......
well i hope everybody can try and help out 1 another here...

 

[saudha]

should be thorough with
stociometry....in case the Q is titration....

• test for aldehydes....
• test for gases...but thts given so no need
• ....how to %error of burette and all.....
• and read the thoery part of redox reactions and know its concept...\
• oxidation and reduction of alcohols aldehydes ketones.....

if i am missing out anything...pls post and amend it.......

 

[saudha]

there are these sites which are helpful.....so am posting it....

Burette: http://www.creative-chemistry.org.uk/alevel/module1/documents/N-ch1-23.pdf

Estimating errors in chem: http://www.creative-chemistry.org.uk/alevel/module1/documents/N-ch1-24.pdf

An idea of how to draw and not titration data: http://www.creative-chemistry.org.uk/alevel/module1/documents/N-ch1-48.pdf

Making saturated solution: http://www.creative-chemistry.org.uk/alevel/module1/documents/N-ch1-49.pdf

 

[saudha]

• A white tile is provided for better observation to spot the colour change during titration.
• The burette and pipette have to be rinsed with the solution before use to avoid any contamination and inaccuracy measurement of the solutions used.
• Value for rough titration is always greater than accurate titration.

Burette & Pipette

 

[saudha]

pippette

 

[saudha]

• Adding 1cm3 reagent is considered "equal amount". Measurement more than 2cm3 is considered excess.
• Take notes of the cations Pb2+, Al3+ & Zn2+. These 3 amphoteric ions exhibits special observations in order to deduce the ions. The ions will form white pptupon adding NaOH drop by drop, and will dissolve in excess NaOH to form a clear solution. When the solution is treated with HNO3, the white ppt will form again. This test is only valid for the 3 ions as mentioned above. The reason behind this is because the hydroxide ions form are insoluble white ppt, and the hydroxide will further react with excess OH- to form a complex ions which are soluble. This can be referred to Le Chatelier's principle.
• Pb2+ can be distinguished from Al3+ by reacting with Cl- to form PbCl2, an insoluble solution.
• Some high-charged ions, eg: Al3+, Fe3+ & Cr3+ can exhibit acidic properties, especially when reacting with CO32- to form CO2 gas.
• Transition element ions, eg: Cu2+, Fe2+, Cr3+ & Mn2+ are coloured solutions. Therefore it's easy to deduce the ions based on their significant colours, for example, Cu2+ is a blue solution.

From left to right, aqueous solutions of: Co(NO3)2 (red); K2Cr2O7 (orange); K2CrO4 (yellow);NiCl2 (green); CuSO4 (blue); KMnO4 (purple).

 

[saudha]

• During calculations, answers which haven't been finalised may be written in 4 or 5 sf (significant figures). Only the final answer for the question need to be rounded up to 2sf or 3sf.
• If unsure with the significant figures needed for the answer, put 3sf instead.
• Approximation sign (≈) cannot be used in answering the question unless stated in the question.
• Reading from burette is always written in 2 decimal places, eg: 25.75 cm3. Note that the 2nd decimal number must be either 0 or 5.
• Pipette reading is fixed at 25.0 cm3.
• Thermometer reading is usually written in 1 decimal place figure, eg: 35.4°C.
• Types of errors:
  • Systematic error: faulty instruments giving zero error (thermometer, stopwatch).
  • Random error: error due to the surroundings (wind, heat).
• Estimated error for burette reading = half of the smallest division = 0.05cm3.
• Oxidation states and ΔH (kJ mol-1) must write + or - .