STANDARDIZATION

Procedure.—­Clean carefully the outside of a weighing-tube, or weighing-bottle, containing the pure sodium carbonate, taking care to handle it as little as possible after wiping.  Weigh the tube accurately to 0.0001 gram, and record the weight in the notebook.  Hold the tube over the top of a beaker (200-300 cc.) and cautiously remove the stopper, making sure that no particles fall from it or from the tube elsewhere than in the beaker.  Pour out from the tube a portion of the carbonate, replace the stopper and determine approximately how much has been removed.  Continue this procedure until 1.00 to 1.10 grams has been taken from the tube.  Then weigh the tube accurately and record the weight under the first weight in the notebook.  The difference in the two weights is the weight of the carbonate transferred to the beaker.  Proceed in the same way to transfer a second portion of the carbonate from the tube to another beaker of about the same size as the first.  The beakers should be labeled and plainly marked to correspond with the entries in the notebook.

Pour over the carbonate in each beaker about 80 cc. of water, stir until solution is complete, and add two drops of methyl orange solution.  Fill the burettes with the standard acid and alkali solutions, noting the initial readings of the burettes and temperature of the solutions.  Run in acid from the burette, stirring and avoiding loss by effervescence, until the solution has become pink.  Wash down the sides of the beaker with a !little! water from a wash-bottle, and then run in alkali from the other burette until the pink is replaced by yellow; then finish the titration as described on page 37.  Note the readings of the burettes after the proper interval, and record them in the notebook.  Repeat the procedure, using the second portion of sodium carbonate.  Apply the necessary calibration corrections to the volumes of the solutions used, and correct for temperature if necessary.

From the data obtained, calculate the volume of the hydrochloric acid solution which is equivalent to the volume of sodium hydroxide solution used in this titration.  Subtract this volume from the volume of hydrochloric acid.  The difference represents the volume of acid used to react with the sodium carbonate.  Divide the weight of sodium carbonate by this volume in cubic centimeters, thus obtaining the weight of sodium carbonate equivalent to each cubic centimeter of the acid.

From this weight it is possible to calculate the corresponding weight of HCl in each cubic centimeter of the acid, and in turn the relation of the acid to the normal.