CHM2046L Scheme of Analysis Lab 2 Unknown

Topics: PH indicator, Solubility, Acid Pages: 1 (467 words) Published: November 3, 2014

Scheme of Analysis for Lab 2 Unknown
Sample Description
Phase, color, odor, crystalline or gel-like?
If crystalline, what is crystal shape – needle-like or powdery? Does it look like a pure substance or a mixture? How many components appear to be present? Tests on original sample
Flame Test
Bushy yellow, orange flame – Na+ is present and possibly K+ and NH4+. Pink-purple flame – K+ is present and Na+ is not. (Possibly NH4+) No color or faint trace Na+ - NH4+ is possible, K+ and Na+ are not. NH4+ Test

Place small amount of sample in vial and add three drops of 6 M NaOH. Cautiously sniff and suspend DIW dampened red Litmus paper to test for NH3+, if necessary. If smells strongly of ammonia and turns suspended litmus paper blue, NH4+ is present. Sample Solubility and Solution Tests

*For DIW-soluble sample, dissolve about ½- 2/3 of sample in about 10-15 mL DIW. pH Test
Fill several vials with solution, and determine pH using indicators (starting with HBtB) pH 1.5: HSO4- must be present, and OH- must be absent
pH about 2-2.5: SO42- may be present in mixture, but not in pure substance pH 3-3.5: OH- not present
pH 5-6: NH4+ present
pH 7: Cl-, NO3-, SO42-, K+, and/or Na+ could be present
pH 9-10: HSO4- and NH4+ not present
pH 13: OH- present and HSO4- and NH4+ not present
K+ Test
If NH4+ is proved to be present, heat small portion (pea-sized) of solid sample on a crucible above flame, and heat until no smoke is rising from crucible. Dissolve remaining contents of crucible in no more than 1-2 mL DIW Add a drop of 6 M HAc (CH3COOH) and 2-3 drops of sodium cobaltinitrite reagent. If yellow precipitate forms, K+ is present

Cl- Test
Place 10-20 drops of sample solution in vial, and add 1 M HNO3 dropwise until solution is acidic. (Test acidity by touching tiny quantities of test solution to blue litmus paper until litmus turns red.) Add one drop 0.02 M AgNO3 to solution

If cloudy precipitate forms, Cl- is present
HSO4- /SO42- Test
Place 10-20 drops of...
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