Laboratory 5: Acids, Bases, and Tums Tums Tums Tums TUMS!

 

Report Requirement: Answer all of the questions/do all the computations requested in italics.  Questions not in italics do NOT need to be answered. You do NOT have to write a formal lab report.  You should write your answers into a word processing program and save the file. Go into the drop box for Lab #5 and cut and paste the answers to each question in the appropriate space.

Report Scoring: 20 points total.  Questions valued as marked.

 

Goals:

  1. Learn to make careful observations
  2. Learn to make hypotheses and design an experiment to test the hypothesis

Materials Needed:

 

Chemicals Needed:

In chemistry, it is important to be able to observe carefully and measure accurately. In this experiment, you will make observations and measurements using several common substances.  

The Neutralizers

One of the most important groups of chemicals can be called the Neutralizers because of their ability to neutralize each other. There are two types of neutralizers: acids and bases. You've probably heard of each of these and could give some examples from around the house.

Question 1: (2 points)  List several examples of household acids and several examples of household bases. Then, give an overview of what you know about the general properties of acids and bases.

Lab Description:

A. Using Indicators to Identify Acids and Bases

How do you identify a substance as an acid or base? One technique is to use an indicator -- a substance that changes color when the acidity of the solution changes. Many of these are the colors that occur naturally in fruits, vegetables, and flowers.

1) Preparation of Red Cabbage Indicator (RCI)

A very useful indicator that we will use is made from red cabbage. Use the following directions and make some RCI .

Take 1 red cabbage and cut it in half. Use a knife to cut that half into shreds. (Throwing it into a blender also helps intensify the color.) Stuff the shredded cabbage into a microwavable bowl (1 pint). Pour in enough water to nearly fill the container. Put a lid on it and microwave for 5 min. (full power); stir; microwave again for 5 min. (full power); stir; microwave again for 5 min. (80 power). Pour off juice into bottle (CAUTION: HOT!) Discard remaining cabbage or use in your favorite kraut recipe. Store RCI in refrigerator until use! It should be a dark blue-purple color. Some suggest adding a couple of tablespoons of alcohol to prevent bacterial growth. 

Story about the stink, CHE 106!!!

sliced cabbage in the microwave (photo by J. Siebenthal)

2. Comparing Red Cabbage Indicator to Red Food Coloring

Sometimes people confuse an indicator with a solution that just happens to have a color. Use the following procedure to compare the two red solutions using common household substances.

a) Collect 1 small cup of vinegar, two white Tums tablets, and 6 clear glasses or cups.

b) Pour a small amount of vinegar into two cups, place crushed Tums tablets into two cups (one in each), and leave the last two cups empty for controls. You may wish to place the cups on a white sheet of paper for the next step.

c) Add about 5 drops of Red Food Coloring (RFC) into one control cup, one vinegar cup, and one Tums cup.  Make observations and prepare a table for your report like the one shown below.

d) Now add about 20 drops of the Red Cabbage Indicator (RCI) into one control cup, one vinegar cup, and one Tums cup.  Make observations and place them into your table.

Indicator

Control

Tums

Vinegar

RCI/RFC experimental results (photo by J. Siebenthal)

RFC (5 drops)

 

 

 

RCI (20 drops)

 

 

 

Question 2: (3 points) Fill out a grid like the one above with your observations and include it in your report.

Question 3: (2 points) Would you choose RFC or RCI for an indicator?   Why?

 

3. Testing Common Substances with RCI.

Place a small amount of each of the following (or your substitutions) into your clear jars (use new jars!): vinegar, Tums - crushed, water, Seven-Up, baking soda, lemon juice, and Milk of Magnesia.  Then, add 30 - 40 drops of RCI to each jar.  Make observations.

Question 4: (3 points) For each of the seven substances, tell whether it is acidic, basic, and neutral BASED ON YOUR OBSERVATIONS.   Explain how you arrived at your assignments (include your observations and what you concluded based on your observation).

4. Introducing the pH Scale

There are several different kinds of acids and bases -- some are stronger and some are weaker. How can we tell which is which? We use something called the pH Scale. We can identify where something is on the pH scale by testing it with pH paper. (If you are interested in obtaining pH paper, please email me and ask.  However, you do not need to have pH paper to do this part of the experiment.) The pH scale is visible with pH paper through color changes similar to the cabbage indicator you made in this experiment (see below).

pH

1

2

3

5

7

9

11

13

14

 

Strong Acid

 

 

 

Neutral

 

 

 

Strong Base

Notice that the scale is backwards from what you might expect: Stronger acid, Lower pH. Also realize that the pH scale is like the Richter Scale for earthquakes, each step differs by a factor of 10 (is 10 times stronger or weaker).   Section 8.4 of your text is a great reference.

Question 5: (2 points) Using your RCI observations thus far, assign pH values to the colors you have observed.

5. Application

As you likely know or have read in the "Health Note" on page 302, acid-base reactions are utilized for relieving upset (acidic) stomachs.  Gastric juice is actually a solution of hydrochloric acid, HCl.  While making an HCl solution at home may be a costly and needlessly dangerous exercise, we can still appreciate the type of reaction by simulating this principle with the acid in vinegar (acetic acid) and antacids.

Measure out about 10 mL of vinegar into a jar and add 30 - 40 drops of RCI.  Note the color of the solution.  Then, crush one tablet of Tums and add it to the jar.  STIR WELL!  Note the color of the solution.   Continue this process until the solution is neutral.

tums and indicator (photo by J. Siebenthal)

Question 6: (3 points) How did you know the solution was neutral?  How many tablets did it take?  What does it mean when a solution is described as "neutral"?

Continue to add several more tablets and continue to note any color changes in the solution.

Question 7: (2 points) What additional color observations have been made?   What do they mean?  What is the implication for treating patients?

 

Finish your experiment by choosing ONE of the following:

Choice A: For Those Who Have a Second Brand of Antacid Available To Them
Repeat Procedure 5 as written above for your alternate antacid (note: if you second antacid is a liquid, use one teaspoon in the procedure instead of one tablet).

Question 8a: (3 points) Are you able to determine which of the two brands of antacid is more effective?  If so, which one?  If not, why not?   Further, can you tell which is better value?  If so, which one?  If not, why not? 

Choice B: For Those Who DO NOT Have a Second Brand of Antacid Available To Them
Continue working with the solution at the end of  Procedure 5.  Begin adding a measured amount of vinegar back to the solution.  Note your observations.

Question 8b: (3 points) What do your observations reveal?  Does this surprise you?

 

This lab was adopted by Kris Young for CHE 106 from a lab previously developed by Tod Treat.