Robbie Kinsey Partner: Debnil Chowdhury Chem. 1312-D TA’s: Russell Dondero & Sylvester Mosley Performed Feb. 16,2000
The objective of this lab was to determine the concentration of phosphoric acid in cola through two different methods: a pH titration and a spectrophotometer method.
pH titration method First, start by preparing a pH meter for use. This was done by using a pH 7.0 buffer solution and pH 4.0 buffer solution. Next the sample of cola to be used must be degassed. This is done by placing 100mL of the cola sample in a flask. Mark the liquid level with a label and cover the top of the flask with a watch glass. Simmer the sample for 20 minutes to expel the carbon dioxide from the sample. After you have stopped heating, and the sample has cooled down to room temperature, add distilled water, if necessary, to restore the liquid level to its preheating height. Before you can start the titration you must standardize the NaOH solution. Rinse a buret once with distilled water and three times with small amounts of the solution of NaOH.. Standardize the sodium hydroxide solution by titrating it against accurately weighed 0.06 g samples of KHP. Rinse a 10-mL pipet once with distilled water and three times with small amounts of the decarbonated cola drink. Use the pipet twice to transfer 20.00 mL of the decarbonated cola drink into a 50-niL beaker. Place a stirring bar in your sample. Place the flask containing the sample on a magnetic stirrer. Immerse the tips of the electrodes in the decarbonated cola. Adjust the speed of the stirrer so that good mixing is achieved without endangering the electrode tips by a flying stirring bar. Read and record the initial pH. Begin the titration by adding 2