CHEM 1 TITRATION LAB

In this experiment the end point of the titration will be signaled by a change in color of an indicator, phenolphthalein. This indicator is RED in basic solutions and COLORLESS in acidic solutions. If you are careful, you can identify the end point accurately by adding the titrant (the liquid from the burette) until the indicator just changes color by the addition of a snuggle drop of the titrant from the burette. If you add too much titrant and overshoot the end point, throw out the sample and start over, proceeding more slowly as you approach the end point.

The instructor will show you how to use a burette properly. If you are right - handed, manipulate the stopcock with your left - hand. Your right hand then is free to swirl the contents of the flask and to mix the contents. IF you are left - handed, reverse the process.

PART 1: ACETIC ACID IN VINEGAR

NOTE; When using a burette, make sure you donít allow the level of the titrate to drop below the level of the last mark on the tube.

Household vinegar is a dilute solution of acetic acid made by the bacterial oxidation of ethanol in cider from apples or from synthetic acetic acid. Mark two Erlenmeyer flasks 1 and 2. Weigh each flask and record its mass. Next, measure 20cm3 vinegar in your graduated cylinder. Pour this vinegar into flask 1. Repeat with flask 2. Weigh the flasks containing the vinegar and record the masses. Add two drops of phenolphthalein in dictator to each flask. Titrate the contents of each flask with 1.00M NaOH solution until the contents of the flask barely turn pink. Record the volume of NaOH used for each titration.

Answer the questions on masses, volumes, moles and percent composition on a worksheet similar to the sample provided in this lab. Compare your results with the information that appears on the vinegar-bottle label. Suggest sources of experimental error or reasons for differences in results.

PART 2: BASIC HOUSEHOLD CLEANERS

NOTE: Though the directions below allow for a solid cleaner, your instructor may require the use of Ammonia, only, for all groups.

Many household cleaners contain compounds such as ammonia (NH3) and sodium hydroxide (NaOH). Such compounds help to loosen grease and dirt. Ammonia and sodium hydroxide are bases. Choose a household cleaner known to contain a base. Determine the amount of base it contains.

Proceed as in Part 1. If your cleaner is a solid, measure out a portion into a weighed flask. Determine the amount of cleaner by a second weighing. If your cleaner is a liquid, measure out about 2 cm3 in your graduated cylinder and pour into our weighed flask. (Why is the exact amount not important?) Weigh.

Add 25cm3 distilled water. If your cleaner was solid Drano, the aluminum present will react. Place the flasks in the fume-hood until the reaction stops. Proceed with titration as in Part 1 except that the contents of the flask will be initially basic (RED WITH PHENOLPHTHALEIN) and will turn colorless when the end point is reached by titration with HCl. This end point is somewhat harder to obtains accurately than the other way around, so titrate carefully.

When one drop of HCI from your burette removes the last pink color, record your volume of 1.00M HCl used. Complete your calculation of the cm3, liters, and moles of HCl used as outlined in the worksheet. both NH3 and NaOH require one mole of HCl to neutralize one mole of base:

NH3 + HCl <----> NH4Cl

NaOH + HCl <----> NaCl + H2O

Now determine which base you have in your cleaner. Proceed with the calculation as in Part 1. Record the percent base as indicated by the manufacturer and compare your results. Suggest sources of experimental error or reasons for differences in results.

PROBLEMS

NOTE: The cleaners used in the lab, above, should contain BASE. Some cleaners contain acids. The acids are added to the cleaners for specific purposes. Reference to acids in the problems, below, refers to these types of cleaners.

1. 5.14g of a household cleaner containing HCl requires 18.5cm3 of 1.0M NaOH solution to neutralize. What is the percent of HCl in the cleaner? Be sure to write out the balanced equation for this reaction.

2. One of the reasons that acids are used in household cleaners is to dissolve "rust" stains from hard water containing iron. These stains may contain Fe(OH)3. Write a balanced equation for the reaction of HCl with Fe(OH)3.

SAMPLE DATA:

NOTE: Make similar tables for recording both acid and base titrations. You will need 2 tables for PART 1, and 2 tables for PART 2 in the lab.

Table 1: Acid or Base in household cleaner

Name of cleaner or Vinegar

Vinegar

Acid or Base contained

CH3COOH

Molecular Mass

 60.06 g

Table 2. Known (acid or base) in Unknown (vinegar or cleaner)

#1

#2

1. Mass of flask + unknown

 140.04 g

 

2. Mass of empty flask

 120.51 g

 

3. Mass of unknown

 19.53 g

 

4. cm3 known (acid or base) to titrate unknown

 12.0 cm3

 

5. Liters of known

 0.0125 L

 

6. Moles of known used

 0.0125 M

 

7. Moles of acid or base in unknown

 0.0125 M

 

8. Mass of acid or base in unknown

 0.75 g

 

9. Percent acid or base in unknown

 3.84 %

 

10. Manufacturers claim

 5.0 %

 

11. Percent deviation

23 %

 

  Sample Calculation based on above data for vinegar. Replace all data with your own.