Lab #12    Acid-Base Titration 
Purpose: the purpose of this lab is to experimentally determine the concentration of an unknown base solution stored in the carboy near the windows.
Procedural Outline: This experiment requires you to perform four separate parts.
Part 1: Creation of an unknown base solution of NaOH
Part 2: Standardization of the unknown base solution.
Part 3: Titration of the base from Part 2 with an unknown acid to experimentally find the exact concentration of the acid solution.
Part 4: Using the acid solution from Part 3, experimentally determine the unknown base concentration.
Procedure: Do only one procedure at a time. Proceed to part two only when completely finished Part 1.
Part 1: Preparation of a NaOH solution of known concentration
  • Find and clean a volumetric flask.
  • Find an appropriate stopper for this flask.
  • Weigh out 10-12 tablets for a 250 mL volumetric flask, or 20-24 tablets for a 500 mL flask, or 30-35 tablets for a 1 L flask. Record the exact mass to two decimal places.
  • Dissolve the solid sodium hydroxide in an approximately half-filled flask. Heat should be released as the solid dissolved so expect the flask to warm up.
  • Once the solid is completely dissolved, fill the flask to the volumetric mark on the neck. (DO NOT go past this mark.)
  •  Stopper and label this flask with your name. This is you're unknown NaOH solution. (Do not lose it. Do not spill it.)
  • Part 1 Data: Mass of NaOH used: ______ g

    Molecular Mass of NaOH:_____ g/mole

    Volume of water used: _________ mL = _________ L

    Part 1: Calculations:

    Moles of NaOH used: ____________ moles

    Estimated molarity of unknown NaOH base solution = _________ mol/L
     

    Part 2: Determining the exact molarity of your unknown base by titration.
  • Weight out 0.75-1.00 grams of dry acid. Record the mass accurately below.
  • Clean a 250 mL Erlenmeyer flask and dissolve this dry acid in 10-15 mL of distilled water.
  • Add 1 mL of bromothymol blue indicator solution to the Erlenmeyer flask.
  • Following the burette filling procedure, load your burette with your unknown base solution.
  •  Repeat this at least 2 more times.
  • Data Table:

    Name of dry acid: ____________________ molecular mass of dry acid used: ________g/mol


    Trial # 1 2 3
    Mass of dry acid used (grams)      
    Volume of base used (mL)      
    The reaction between the dry acid and the sodium hydroxide is:
     
    Calculations: Using the reaction from above, determine the molarity of the unknown base:
     
    Trials # 1 2 3
    Moles of dry acid used (moles)      
    Moles of unknown base used (moles)      
    Molarity of unknown base (mol/L)      
    Average molarity (mol/L)  

     
    The average molarity you calculated is the exact molarity of the NaOH solution. It is now standardized. Write the average molarity on the flask. Store it away safely, as you will need it for Part 3.
    Part 3: Standardizing an acid solution by titration.
    We will use the standard bottles supplied in the lab. These bottles have various molarities written on them and this is normally good enough for everyone else. It is not good enough for you. You need to determine the molarity to at least three decimal places.
    Procedure:
  • Fill your burette with your base solution from Part 2.
  • Obtain a 100 or 250 mL Erlenmeyer flask, rinse it with distilled water to make sure its clean.
  • Using a 5, 10 or 25 mL volumetric flask (your choice) add a sample of your acid to the Erlenmeyer flask.
  • Add 1 mL of bromothymol blue indicator solution to the Erlenmeyer flask.
  • Titrate this unknown acid against your known standardized NaOH solution.
  • Repeat this titration at least twice more. (You do not need to use the same amount of acid each time.)

  •  
    Data Table
    Trial #   1       2        3   
    mL's of HCl used            
    mL's of NaOH used         
    Calculations: Using MaVaCa = MbVbCb calculate the molarity of the acid.
     
     
     
     
     
    Trial #    1       2       3   
    Molarity            
    Average Molarity   

     
    Part 4: Titration of the unknown base with the standardized acid from Part 3.
    Procedure:
    • Fill your burette and flush it with some of your acid to neutralize the base in the burette.
    • Flush the acid out with several washings of distilled water.
    • Fill your burette with about 25 mL of acid and give the burette a final cleaning with acid.
    • Fill the burette with your unknown acid solution.
    • Using a clean volumetric pipette (5, 10 or 25 mL) obtain some of the unknown base solution and put it into a clean 100 mL Erlenmeyer flask. Record the volume used below.
    • Add 1 mL of the bromothymol blue indicator solution to your Erlenmeyer.
    • Titrate the base against your known acid until neutralized.
    • Repeat steps iv) to vii) at least two more times.
    Data Table
    Trial #    1       2       3   
    mL's of HCl used            
    mL's of NaOH used         

     
    Calculations: Using MaVaCa = MbVbCb calculate the molarity of the acid.
     
     
     
     
     
                                        Trial #                                     1               2                 3       
    Molarity            
    Average Molarity   

     
    Titration Analysis 
    Fill in the following information from your lab.  this sheet will constitute your lab report.
    Part 1:  Creation of your base solution
    Name of Base used:  
    Grams of base used:  
    Volume of Volumetric flask used:  
    Estimated Molarity  
    Part 2: Standardization of your base solution

    Trial 1
    Trial 2
    Trial 3
    Grams of Dry Acid Used:      
    Volume of Base Used:      
    Molarity of you base      
    Average Molarity of the base I created is: ___________________M
     
    Part 3:  Finding the Molarity of the Unknown HCl Solution

    Trial 1
    Trial 2
    Trial 3
    Volume of unknown HCl solution used      
    Volume of your base used      
    Molarity of the unknown HCl solution      
    Average Molarity of the unknown HCl solution is: _____________M
     
    Part 4: Finding the Molarity of the unknown NaOH solution

    Trial 1
    Trial 2
    Trial 3
    Volume of unknown HCl solution used                 
    Volume of NaOH used              
    Molarity of unknown NaOH solution               
    Average Molarity of the unknown NaOH solution is: _____________ M