Acids, Bases, and Buffers 2: Unknown Solutions Overview Getting Started Techniques Procedure FAQ Full Lab Manual Introduction & Goals Chemistry & Background Key Questions Prelab Problems Safety Procedure In Your Write-up Appendix Experiments Index ChemLab Home		Procedure You and your partner will devise your own methods for answering the questions stated above. To make the best use of your time in the lab, you are urged to meet and plan a strategy with your partner before coming to lab. A detailed procedure should be included in your prelab write-up. The following equipment will be available in the lab, in addition to the glassware in your tray: 10 and 25 mL pipets 50 mL burets pH meters The following solutions will be available for your use: Standardized solutions of approximately 0.1 M NaOH and HCl. Indicator solutions of phenolphthalein, methyl red, and cresol red. Unknown samples, dispensed by repipet in 50 mL aliquots. You and your partner will choose one lettered unknown and one numbered unknown. The concentrations of acids and bases will be approximately equal to those of the standard acid and base solutions available for titration. Be certain to record the number and letter of your unknown solutions in your lab notebook. You will also need to record the concentrations of stanardized acid and base solutions used in titration. When you plan and implement your experiments, first consider the qualitative questions, then the quantitative ones. A precise titration is not necessary to determine whether a solution is an acid, a base, or a buffer. Always perform simple experiments first and do not perform any experiments that are more complicated (or time-consuming) than needed to answer the question at hand. Always do a calculation using the approximate concentrations given in this manual to determine the approximate expected results, before you start an experiment. When you have determined the nature of your solutions and identified them as acids, bases, or buffers, you are not done. You need to do more quantitative experiments to determine the concentration of acid and base solutions accurately. Rather than using a pH meter to determine the endpoint for this type of titration, select an appropriate indicator to enable you to observe the endpoint visually. The appendix about indicators may help you make a selection. You may also need to perform further experiments on a buffer solution to identify its constituents. Look carefully at the table of possible acids and bases and be sure you can conclusively identify your solutions from your titration data.
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