ANACHEM LAB PRELIMS

• Cleanliness is essential in carrying out chemical analysis.
• All apparatus should be thoroughly cleaned with tap water and soap and rinsed with distilled or deionized water
• Do not use distilled water for washing! Remember that soap and other cleansing agents contain substances that may contaminate your solutions
• Avoid contamination from crucible tongs and other metallic apparatus.
• Protect your unknown solutions and reagents from rust falling from some of your apparatus.
• Keep their containers covered always.
• Use paper towels to wipe up all spilled materials.
• Arrange working materials in an organized manner
• Operations involving the production of fumes should be done under the fume hood.
• Never dip your medicine dropper into the reagents and never return any reagent to the bottle.
• Never allow the dropper tips to come in contact with anything outside the reagent bottle.
• Do not rest the dropper against the inside of the container into which the reagent is being added.
• Always hold the dropper just above the mouth of the vessel and allow the reagent to fall into the vessel.
• Never pour the reagents to your reaction mixture directly from their bottles.
• In getting solid reagents, pour out the solid from the reagent bottle to a clean and dry watch glass and then add the reagent from the watch glass to your reaction mixture by means of a dry, clean spatula or reagent scoop.
• Do not place solid reagents on papers.
• Reagents are solids or solutions of known substances, the reactions of which with the unknown identify or help identify the latter.
• Test solutions are very dilute solutions which are used to demonstrate the chemical behavior of a given constituents towards certain reagents.
• The amount of reagents to be added is of course dependent on the amount of the constituents to be separated or precipitated and this we know is unknown.
• the amount of reagent required to dissolve a precipitate shall be determined by the amount of precipitate which obviously cannot be determined beforehand.
• Precipitation may have for its purpose either separation or identification
• First, precipitation must be complete
• second, the grains of the precipitate must be sufficiently coarse for an easy and efficient separation.
• To make the separation complete, an excess of the reagent is added.
• A large excess of the reagent should be avoided, however, since in many instances it will increase the solubility of the precipitate or interfere with succeeding operations.
• Centrifuge and repeat the foregoing procedure until on addition of a drop of reagent, no precipitate forms in the clear layer liquid. This marks the point exactly when enough reagent has been added.
• Precipitate: a solid that forms as the result of a chemical reaction in aqueous solution.
• Due to the formation of supersaturated solution or colloidal suspension, precipitation is often slow and incomplete.
• Supersaturation may be broken by stirring, and addition of electrolytes such as acids or ammonium salts.
• It is essential that the solution to be tested as well as the reagent be absolutely clear.
• Filtration is the most common method of separating the solid portion from the liquid portion of a mixture.
• supernatant liquid is also called mother liquor
• A few squirts of distilled water from a wash bottle should be used to detach the last traces of solid adhering to the walls of the vessel.
• In semi-micro work, filtration is replaced by the use of the centrifuge, which is much more rapid.
• In operating the centrifuge, always balance it symmetrically and do not spin it in an undue length of time
• • About 40 seconds will be enough to make most precipitates settle.
  • The supernatant liquid is then separated by decantation or by means of a pipette or dropper.
• Precipitates should be freed of the adhering filtrate by washing; otherwise, some of the materials in the filtrate that wet the precipitate may cause trouble in the analysis.
• The enclosed wash liquid will dilute or in some instances partly neutralize the reagent to be added next.
• Before treating the precipitate further, the enclosed wash solution should be removed as completely as possible
• This is done by pressing the precipitate between dry filter papers if the precipitate is in the filter paper.