chemlab - common lab techniques

• Common Laboratory Techniques in Analytical Chemistry include qualitative analysis, which determines the identity of the chemical species, and quantitative analysis, which determines the relative amount of the chemical species in each amount of sample.
• Understanding the uses of the reagents is helpful when planning an analysis.
• The four most commonly used reagents are 6M HCl, 6M HNO3, 6M NaOH, 6M NH3.
• Macro analysis in Analytical Chemistry involves an amount of analyte that is more than 0.10 grams (100 mg), such as a suspected pollutant in a 1-gram soil sample.
• Semimicro analysis in Analytical Chemistry involves an amount of analyte between 0.010 - 0.10 grams, such as the amount of drug in a 5-mg sample of powder or determination of glucose in a blood sample.
• Micro analysis in Analytical Chemistry involves an amount of analyte between 10 -4 and 10 -2 grams, such as a suspected pollutant in a 1-gram soil sample.
• Ultramicro analysis in Analytical Chemistry involves an amount of analyte less than 10 -4 grams, such as determination of arsenic, boron, nickel or silicon in the body through urine test.
• Reagent Grade in Analytical Chemistry confirms to the minimum standards set forth by the Reagent Chemical Committee of the American Chemical Society (ACS).
• Primary-Standard Grade in Analytical Chemistry are chemicals with extraordinary purity prepared by National Institute of Standards and Technology (NIST).
• Special-Purpose Grade in Analytical Chemistry are chemicals prepared for a particular or specific application.
• In Analytical Chemistry, the best grade of chemical should be selected for analytical work, and the top of every container should be replaced immediately after removing reagent.
• In Analytical Chemistry, apparatuses should be washed properly before use by washing liquid detergent, and it should be washed with tap water then several small portions of distilled water.
• In Analytical Chemistry, evaporation may be necessary in some procedures to reduce volumes of samples containing nonvolatile solutes.
• When reading volume in an apparatus, always read in eye level at lower meniscus.
• To remove the supernatant, carefully pour or pipette the solution away from the solid.
• Litmus paper changes from blue to red when the sample changes from being basic to acidic.
• If it says make it basic, use red litmus paper.
• If the procedure says make it acidic, use blue litmus paper.
• Apparatuses used in analytical chemistry for precisely measuring volume are the following: J
• For a very small amount of sample, complete precipitation can not be tested using 5 ml of that sample.
• The purpose of washing precipitates is to ensure that all interfering ions will be washed away from the sample.
• Clear centrifuge is usually transferred to another test tube.
• Chlorides and nitrates can be evaporated by adding sulfuric acid.
• Centrifuge and discard washings.
• Nitrate ion and nitrogen oxides can be removed by adding urea.
• The sample can be placed in an evaporating dish and heated over in a water bath.
• Add one drop of acid or base to the sample then stir.
• Ions in a group are separated from each other after each separation stage in qualitative analysis.
• Centrifuge is a device by which a centrifugal force produced by an electric motor speeds up the rate of setting of a precipitate.
• In qualitative analysis, ions are removed in groups from the initial aqueous solution, then testing is conducted for the individual ions in each group.
• Supernatant Liquid is the resulting liquid after a mixture of liquid and solid has been left to settle out or centrifuged to separate the two.
• Separations in qualitative analysis rely on different characteristics of ions, which may involve redox reactions to change oxidation state, differential solubility in an acid, base, or water, or precipitating certain ions.
• The test tube containing the solution to be centrifuged should always be balanced by placing another test tube, containing an equal volume of water in the centrifuge opposite the solution.
• It's easy to contaminate the sample through poor laboratory technique, so it's important to adhere to certain rules in qualitative analysis: use distilled water or deionized water, clean glassware prior to use, and avoid putting a reagent dropper tip into the mouth of a test tube.
• The solubility product constant (Ksp) describes the equilibrium between a solid and its constituent ions in a solution.
• If the solid becomes re-suspended as the supernatant is removed, centrifuge the sample again.
• In an educational setting, the concentrations of the ions to be identified in qualitative analysis are approximately 0.01 M in an aqueous solution.
• When removing the supernatant using suction, be careful to avoid expelling air bubbles into the solution and keep the tip of the dropper away from the solid.
• Qualitative analysis is used to identify and separate cations and anions in a sample substance, unlike quantitative analysis which seeks to determine the quantity or amount of sample.
• Ammonium chloride can be removed by adding concentrated Nitric acid.