Experiment 12 Determination of Protein in Macaroni by the Kjeldahl Method

Experiment 12 Determination of Protein in Macaroni by the Kjeldahl Method 

Weigh between 0.10 and 0.13 g of the macaroni sample on the analytical balance using weighing paper. Add this sample to a clean, dry 100-mL Kjeldahl flask to avoid having sample particles stick to the neck of the flask. Set aside for a few minutes (inside a beaker so that it stays upright) while you do step 4. 

Set the 250-mL beaker in place on the platform of the distillation apparatus in the fume hood such that the glass tip of the condenser is under the surface of the solution in the beaker. Make sure that the stopcock on the upper left of the distillation unit (the addition stopcock) is closed. Also make sure that the other stopcock (the siphon stopcock) is closed. Add the contents of the Kjeldahl flask to the funnel above the addition stopcock. Open this stopcock to deliver the solution fairly 

Open the siphon stopcock. The contents of the mixing chamber should siphon out. Close the siphon stopcock. Rinse the mixing chamber several times by adding small amounts of distilled water through the addition stopcock and subsequently siphoning through the siphon stopcock. This prepares the apparatus for the next student. 

Titrate the solution in the receiving vessel with the standardized 0.01 N NaOH until there is a color change from pink to light yellow. Calculate the percent protein in the sample as follows. A factor (F) is used to convert the weight of nitrogen to the weight of protein. 

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