1. Technology and Engineering
CHEMICAL ANALYSIS

2. Determination of alluminium
SMK Negeri 13 Bandung

3. Objectives….
After this session, the students are expected to be able :
- to explain the steps of determination of alluminium
- to explain the objectives of every step
- to explain the function of reagents
- to arrange the planning of determination of alluminium according to the job sheet
- to conduct the determination of alluminium
- to do the calculation in the determination of alluminium
- to arrange the report of the determination of
alluminium
Teknologi dan Rekayasa

4. Procedure Weigh out accurately about 1,8 gram alluminium sample salt
Rinse and dissolve in 200 mL of water then add 5 gram of ammonium chloride, a few drops of methyl red indicator and heat just to boiling.
Add pure dilute ammonia solution (1:1) drop wise from a burette until the color of the solution change to a distinct yellow
Teknologi dan Rekayasa

5. Procedure….
4. Boil the solution for 1 or 2 minute and filter at once through a quantitative filter paper (what number?)
5. Wash the precipitate thoroughly with hot 2 percent ammonium nitrate or chloride solution made neutral with ammonia solution to methyl red indicator.
6. Place the paper with the precipitate in a constant weighed crucible.
Teknologi dan Rekayasa

6. Procedure…
7. Dry, char and ignite for minutes with a Fisher or Meker high temperature burner. (12000C)
8. Allow the crucible covered with a well fitting lid to cool in a desiccator and weigh as soon as cold. Ignite to constant weight.
9. Calculate the percentage of alluminium.
Teknologi dan Rekayasa

7. Teknologi dan Rekayasa

8. Teknologi dan Rekayasa

9. Teknologi dan Rekayasa

10. Teknologi dan Rekayasa

11. Teknologi dan Rekayasa

12. Teknologi dan Rekayasa

13. Teknologi dan Rekayasa

14. Teknologi dan Rekayasa

15. Teknologi dan Rekayasa

16. Teknologi dan Rekayasa

17. Teknologi dan Rekayasa

18. Teknologi dan Rekayasa

19. Teknologi dan Rekayasa

20. Discussion…..
The alluminium is precipitated as the hydrated oxide by means of ammonia solution in the presence of ammonium chloride.
The gelatinous precipitate is washed, converted into the oxide by ignition and weighed as Al2O3
Teknologi dan Rekayasa

21. Discussion….. alluminium hydroxide is amphoteric in character :
Al(OH)3 + 3H+  Al3+ + 3H2O
Al(OH)3 + 3OH-  AlO H2O
Teknologi dan Rekayasa

22. Precipitation Begin at pH 4
Complete between pH 6,5 – 7,5.
The pH employed for precipitation must be controlled
The pH range adjusted with the aid of methyl red as indicator.
Teknologi dan Rekayasa

23. The Ammonium chloride
pH controlling as a buffering agent
assists the coagulation of initially colloidal precipitate
reduces to a minimum co precipitation of the divalent metal such as calcium and magnesium.
Teknologi dan Rekayasa

24. Readily filterable precipitate
Hot precipitation
Readily filterable precipitate
Slow/gradual
Big size
Co agullated
Teknologi dan Rekayasa

25. Washing of precipitate
Use no pure water because alluminium hydroxide will readily peptized and will run through the filter.
Use 2 percent neutral NH4Cl or NH4NO3 solution .
Teknologi dan Rekayasa

26. Washing solution….
NH4Cl or NH4NO3
electrolyte, prevent the peptisation, stabilize the co agulated precipitate
Neutral
prevent the dissolving reaction to be Al+3 or AlO2-
Hot
Co agullation (Help to stabilized the coagulated precipitate)
Teknologi dan Rekayasa

27. Ignition At least 12000C 2 Al(OH)3 Al2O3 Ignite in a silica crucible
(porcelain is slightly hygroscopic when heated to a high temperature)
Use Fisher or Meker burner. (The best procedure is in an electric furnace.)
Teknologi dan Rekayasa

28. Ignition Alluminium oxide is formed at 9000C, but hygroscopic
A stable and pure alluminium oxide is formed at 12000C
Teknologi dan Rekayasa