Mrs. Torres
CLASS SET
Acids, Bases, and Indicators
Objectives
 Identify common household acids and bases.
 Identify distinguishable characteristic properties of acids and bases.
 Observe the behavior of strong acids and bases from weak acids and bases.
 Determine the pH of various solutions using indicators.
 Categorize solutions as acid or base by pH scale
Standards Addressed
Chemistry
5a. Students know the observable properties if acids, bases, and salt solutions.
5c. Students know strong acids and bases FULLY dissociate and weak acids and bases PARTIALLY
dissociate.
5d. Students know how to use the pH scale to characterize acid and base solutions.
Investigation & Experimentation
Investigate:
1.
Your teacher will provide you with samples of some of the materials listed below. Place a small
amount of each solution in a separate well of a well plate. Add a small piece of polished zinc (or
magnesium) to each of the solutions.
A) Make a data table to record your observations.
Hydrochloric acid (HCL(AQ))
Lemons or orange juice (citric acid)
Vinegar (acetic acid, CH3COOH)
Sulfuric Acid (H2SO4)
Mineral water
Carbonated beverage such as Spite or Seven Up (Contains H2CO3)
Milk
Dishwashing solution (Ivory, Polmolive, Fabuloso)
Sodium Hydroxide (NAOH)
Milk of Magnesium (contains Mg(OH)2)
Apple Juice (malic acid)
Potassium Hydroxide (KOH)
Calcium Hydroxide (Ca(OH)2)
Household Ammonia (NH3 or NH4OH)
B) Which substances reacted with the metal? How could you tell? What do these substances have
in common? (Consider the chemical formulas listed for some of the substances.)
C) Which substances did not react with the metal? What do these substances have in common?
(Consider the chemical formulas listed for some of the substances)
2.
Place small amounts of each solution you used in step 1 in a separate beaker.
Test the solutions with one or more common laboratory indicators. (Your teacher will provide acidbase indicators like blue litmus paper, red litmus paper, phenolphthalein, bromothymol blue, methyl
red) Indicator papers are activated by simply placing a small piece of paper into the solution and
Mrs. Torres
CLASS SET
noting any color change. If the indicator is a solution, add a drop or two to the substance being
tested and note any color change. You will need to use fresh test solution if you want to test with
more than one indicator solution.
A) Make a chart and record your observations.
3.
Use your observations and previous experiences to answer the following questions.
A) Make a list of some of the observable properties for acids and bases.
For Example:


4.
5.
6.
7.
How do substances containing acids and bases taste? You should never taste substances in a
lab, but you have probably been able to taste vinegar and lemon juice at home, or you may
have accidentally gotten soap in your mouth.
How do acids and bases feel. You must be very careful when handling chemicals at home or
in the lab. However you’ve probably had the experiences of touching cleaning materials,
such as soaps and floor cleaners. Think about vinegar or citrus juice. How do they feel on a
cut, on your skin, or on a canker sour in your mouth?
The pH scale is also used to describe acids and basses. This number scale range from 0 to 14. Acid
solutions have a pH level less then 7. The more acidic an acid is the lower the pH number. Base
solutions have a pH higher then 7. The more basic a solution is the higher the pH. Neutral solutions
have a pH of 7. There are a number of ways you can use to measure pH. You will use pH paper
and/or a universal indicator solution.
Determine the pH of some of the substances you used before in Step 1.
A) Make a data table that includes the name of the substance, the pH test, and whether the solution
is an acid, a base, or a neutral substance.
B) You may have used both pH paper of universal solution. Both of these are made from a
combination of indicators, in order to produce a continuous range of colors through out the pH
scale. Methyl red is a chemical that changes colors from red to yellow when the pH is between
4.2 and 6.3. Thymolphthalein is a chemical that changes from colored to blue if the pH is
between 9.4 and 10.6. Thymol blue is a chemical that changes from red to yellow when the pH
is between 1.2 and 2.8.
C) How could these three chemicals be used to create an indicator scale? What are the limitations
when limited to these three chemicals?
Use the pH paper to test additional household products to determine which are acids and which are
bases. Your teacher may give you some pH paper to take home with you.
A) Make a list of common acids and bases found in your school or home. When possible, include
both the name and formula for each substance you tested.
Dispose of all chemicals as directed by your teacher. Clean up workstation and put away materials
as instructed. Wash your hands.
Analysis
1. What is pH and what does it describe?
2. Describe the differences between acids and bases.
3. Describe the properties of an acid. Give two examples of acidic substances.
4. Describe the properties of a base. Give two examples of basic substances.
5. What do the chemical formulas for all acids and bases have in common?