How Much Acid is In Your Soda



How Much Acid is In Your Soda?

Materials:

 

3 Different brands of soda pop (Pepsi, Mountain Dew, Sprite/Sierra Mist)

Prepared flat versions of each soda type

Phenolphthalein

1.0 M NaOH

Disposable pipets

Distilled water

2 - 250 mL Erlenmeyers flasks

2 - 100 mL beakers

1 - 10 mL graduated cylinder

White sheets of scrap paper

BACKGROUND

There are several ingredients in soda pop that contribute to its acidity.  In this lab, you will perform a TITRATION to determine the difference in acidities in different types of pop.  A titration is an experimental technique which allows determination of acid concentration in a substance, by adding a known volume of base (with a known concentration) until a light pink color appears in the reaction vessel.  The pink color appears due to an INDICATOR which is added to the substance being tested.  The indicator, in this case phenolphthalein, is colorless in acid and turns pink in the presence of base.  Since our pop is already acidic, we can add the indicator, then add base just until the color changes.  This is called the ENDPOINT.  This type of experiment is a very common analytical technique used in various fields of study.

DIRECTIONS

You will be testing 3 kinds of pop, specifically a fresh and flat version of each, so there are 6 tests to do.  You will work in groups of four for this lab. If you go past the endpoint redo that test.

1.  Open the can of pop and carefully pour about 30mL into a small beaker, share can with the other groups on your side of the lab.

***NOTE***

Pour the pop CAREFULLY!!  You DON’T want it to fizz!  If it fizzes and loses its carbonation it will be just like the flat pop.

2.  From the pop you poured into the small beaker measure out 20.0mL into a graduated cylinder and pour into an Erlenmeyer flask.

3.  Using distilled water bottle rinse remainder of pop from graduated cylinder into the flask.

4.  Now add about 25 mL distilled water into the Erlenmeyer flask with the soda.

5.  When you are testing the Pepsi make 2 of these solutions, one to use as a comparison for color and the other to test.

6.  Add 7 drops of phenolphthalein indicator to the flask

7.  Rinse sides of Erlenmeyer with distilled water.

8.  Place flask on sheet of white paper so you can see the color change more clearly

9.  Add 1.0M NaOH (base) 1 drop at a time; keeping track of drops added. Have one group member swirl the flask as another adds the base.

10.  As soon as you notice a light pink color change which remains after you swirl the solution you have reached the endpoint.

 

DATA:

|place |Pepsi |Flat |Sierra Mist |Flat |Mt. Dew |Flat |

| | |Pepsi | |Sierra Mist | |Mt. Dew |

|Number of drops of NaOH added |place |place |place |place |place |place |

|to reach endpoint | | | | | | |

|Observations | | | | | | |

ANALYSIS/CONCLUSION QUESTIONS:

1.  Which contains less acid, the fresh or flat pop?  How do you know?  Why do you think that is?

 

 

 

2.  What are the possible ingredients in each soda that contribute to their respective acidities?

 

 

 

3. What is the concentration of the acid in each soda tested?

Use the formula: MAVA = MBVB

|Pepsi |Flat |Sierra Mist |Flat |Mt. Dew |Flat |

| |Pepsi | |Sierra Mist | |Mt. Dew |

| | | | | | |

| | | | | | |

| | | | | | |

4.  Phosphoric acid is an ingredient in Pepsi, the structural formula is:

When this acid dissociates 3 H+ (protons) are released.  Thus, it can be said that 3 equivalents of acid (remember an acid donates H+ into solution) are produced for every one mole of phosphoric acid.  How many moles of base do you think you would have to add to neutralize this acid (think: how many base equivalents (OH-) are needed to neutralize the acid (combine with H+ to make HOH)?

1 H3PO4  +   NaOH [pic] 3 H2O  +  1 Na3PO4

5. Let’s assume the pop only contains phosphoric acid. If you had to add 20 drops of the NaOH to neutralize the Pepsi, and there are 16 drops NaOH in 1 mL of NaOH, how many grams of phosphoric acid were in your 20.0 mL sample?

 

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download