Cheese and Grapes

Acid-Base Titration

Purpose: Calculate the concentration of an acid by neutralizing it with a base with a known concentration.

Materials: Dilute hydrochloric acid (HCl)
                1M sodium hydroxide (NaOH)
                Phenolphthalein indicator
                Erlenmeyer flask
                Droppers
                50ml. graduated cylinder
                10ml. graduated cylinder

Procedure: Put fifty ml. of dilute HCl in the Erlenmeyer flask.   Add a small amount of phenolphthalein indicator to the HCl.   Use the graduated cylinder to get ten ml. of 1M NaOH.   Slowly add a few drops of base from the graduated cylinder into the acid in the flask.   Swirl the flask until the pink color goes away.   Continue to add the base and swirl the color away.   As more base is added, it should take longer for the pink to disappear.   When the pink starts to stay for at least several seconds add one drop of base at a time.   When the pink will not go away, do not add any more base.   Record the amount of unused NaOH in the graduated cylinder.   Carefully pour the liquids down the sink and rinse all of the equipment.

Data:
|Original volume of NaOH                                           |10.0ml.                                                           |
|Unused volume of NaOH                                             |3.5ml.                                                           |
|Volume of NaOH used                                               |6.5ml.                                                           |
|Moles of NaOH                                                     |.0065 moles                                                       |
|Moles of HCl                                                     |.0065 moles                                                       |
|Concentration of HCl                                             |.13M.                                                             |

Conclusions:   Phenolphthalein is...