Qualitative Analysis of Cations Overview Getting Started Techniques Procedure FAQ Full Lab Manual Introduction & Goals Chemistry & Background Key Questions Prelab Problems Safety Procedure In Your Write-up Experiments Index ChemLab Home		Using pH Paper Place a piece of pH paper on a clean watchglass. Use a stirring rod to remove a drop of solution from your test tube. Touch the stirring rod to the paper and compare the color to the pH key on the package. Note that the sample should be brought to the paper, not the other way around. This keeps your sample from being contaminated by the dye in the pH paper. Heating in a Water Bath Place your test tube, supported by a holder, in a bath of hot water heated by a stirrer-hotplate. Adjust hotplate setting so water boils gently. Check that the water in the bath is clean and that the beaker is not cracked. Keep water baths at least half-full with distilled water. To avoid build up of H2S, hot water baths should be placed in the fume hood. Separating Solid & Solution After centrifugation, the solution should be clear and the solid should be collected in the bottom of the test tube. Remove the solution by decanting, or pouring, it away from the solid. Wash the precipitate by first adding a small amount of water and swirling the precipitate. Then centrifuge again and decant, combining the centrifugate with the previous one. This will ensure that all soluble ions are removed from the solid. The decanted solution should be completely clear, with no cloudiness, which indicates incomplete separation of the liquid and solid. All insoluble ions must be removed from the solution to avoid masking further tests performed on the centrifugate. You can also remove the solution from a centrifuged precipitate by using a disposable pipet to carefully draw off the liquid. This is an effective alternative to decanting the solution, but the precipitate must be washed to remove all soluble ions and the solution must be completely clear, to be sure all solid ionic salts are removed. Technique Links Centrifugation
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