Neutralization Reactions Lab
Another way to make salt water
Introduction and Purpose:
Name: ___________________________
Date: _______________ Period: ______
In this lab you will explore the interaction of an acid and a base. This is the same reaction that takes place
when you take an antacid medication such as Tums, Mylanta, Rolaids, or Maalox. The substances just listed
are all bases, and they are used to neutralize the excess stomach acid that may be produced by your body.
This extra acid produced in your stomach may begin to break down a protective coating on the stomach innerwall, which produces a rather uncomfortable feeling. By introducing a base (or an anti-acid, shortened to
antacid), the excess acid in your stomach is neutralized; it is made neutral.
In this lab, you will mix the strong acid found in the human stomach—Hydrochloric Acid (HCl)—with a base
called Sodium Hydroxide (NaOH). This will not be a simple physical mixture; rather, a chemical change will
occur. You will be able to observe this change using two liquid indicators. These indicators work like pH
paper strips and litmus paper by changing color in the presence of acids and/or bases. The two liquid
indicators that will be used are Bromothymol Blue (BTB) and Phenolphthalein. Their indicating colors are
listed below for acids and bases.
Bromothymol blue indicates if a substance is a base by turning blue. If the substance is an acid, it turns
yellow. A purely neutral substance appears as a pale green color. Phenolphthalein is pink in a base. It is
only a base indicator. If a substance is an acid OR neutral, phenolphthalein is clear.
Indicator
BTB
Phenolphthalein
Color in neutral
substance
Pale Green
None (clear)
Color in presence of
Acid
Yellow
None (clear)
Color in presence of
Base
Blue
Pink
Materials:
2 medium test tube, distilled H2O, Bromothymol Blue, Phenolphthalein, .1M HCl, .1M NaOH
Lab Procedure: (After performing each step, place a small check mark by the number.)
_____ A)
_____ B)
Label one test tube BTB and the other test tube Phenol.
Fill each test tube with 5 ml distilled water using a graduated cylinder for precise
measurement.
_____ C) Put 10 drops of Bromothymol Blue (BTB) into the BTB flask, and 10 drops of
Phenolphthalein into the Phenol flask. (Bromothymol Blue flask)
_____ D) Add 2 squirts of NaOH to the flask. (List observations in the data table below)
_____ E) Using dropper Slowly add drops (keep a count!) of HCl to the flask, one drop at a time,
allowing 10 seconds after each drop for the reaction to stabilize and mix thoroughly. Stop
adding drops when the color fully turns to a pale yellow or green. Record the number of
drops in the data table.
Step F: 2 Squirts NaOH
Observations:
Bromothymol Blue Observations & Data
Step G: # of HCl drops Step H: 1 drop HCl
Observations:
Observations:
Step I: 3 drops NaOH
Observations:
Number: _____
Acid, Base, or Neutral?
Acid, Base, or Neutral?
Acid, Base, or Neutral?
Acid, Base, or Neutral?
Question 1: Before adding the acid (HCl), the distilled water with the base (NaOH) in it was blue.
After adding enough drops of acid, the liquid turned to a pale green, which indicates a
neutral substance. This reaction between HCl and NaOH is called a neutralization
reaction.
What kind of change (physical or chemical) did the acid and base undergo when they
were mixed together in equal amounts? ______________________
What is your evidence? __________________________________________________
Question 2: Predict what will happen if you add one single drop of NaOH to the flask. _________
___________________________________________________________________
Question 3: Predict what will happen if you add one single drop of HCl to the flask. _________
___________________________________________________________________
_____ F) Add 1 single drop of HCl to the flask and list observations in the data table.
_____ G) Add 3 drops of NaOH to the flask and list observations in the data table.
Question 4: The reaction between HCl and NaOH can be represented by a chemical equation:
HCl + NaOH  NaCl + H(OH)


What is the substance NaCl commonly called? ______________________________
H(OH) can also be written H2O.
What is this substance commonly called? __________________________________
****WOWZA**** It turns out that ALL acid-base reactions produce a salt and water. The salt
however does not have to be NaCl, it can be any ionic compound.
A neutralization reaction is a reaction between an acid and a base
which produces two neutral substances—a salt and water.
_____ H) (Phenolphthalein flask) Add two (2) squirts of HCl
_____ I) Slowly add drops (keep a count!) of NaOH to the flask, one at a time, allowing 10
seconds after each drop for the reaction to stabilize and mix thoroughly. Stop adding
drops when the color turns to a very pale pink. Record the number of drops in the table.
_____ J) Once neutralization occurs proceed to next step
_____ K) Add 1 single drop of NaOH to the flask and list observations in the data table.
_____ L) Add 3 drops of HCl to the flask and list observations in the data table.
Step K: 1 Squirt HCl
Observations:
Phenolphthalein Observations & Data
Step L: # of NaOH drops
Step M: 1 drop
NaOH
Observations:
Observations:
Step N: 3 drops HCl
Observations:
Number: _____
Acid, Base, Neutral, or
Unknown?
Acid, Base, Neutral, or
Unknown?
Acid, Base, Neutral, or
Unknown?
Acid, Base, Neutral, or
Unknown?
Conclusion Questions
Question 5: What are the differences between the two indicators (BTB and phenolphthalein) in how
they behave…
…in the presence of acids? _______________________________________________
_____________________________________________________________________
…in the presence of bases? ______________________________________________
_____________________________________________________________________
…in the presence of a neutral substance? ___________________________________
_____________________________________________________________________
Question 6: Knowing you have a solid chemistry background, your boss at work has politely asked
you to sort the chemicals in a storage closet into a group of cleaning solutions and noncleaning solutions. When you look in the closet for the first time, you see shelves full of
identical containers with no labels. The liquids inside the containers are not all the
same. Remembering this way cool acid-base lab from ICP, you decide to ask your
boss to order an indicator that will help you determine which solutions are cleaning
solutions. Your boss agrees, but she says to keep the cost of the indictor to a
minimum. Looking in a chemical supply catalogue, you notice that Bromothymol Blue
costs $20.00 for every 10g, and Phenolphthalein costs $8.00 for every 25g.
Discuss which indicator you will order. Be sure to include an explanation for your
choice in terms of the expected reactions of BTB and phenolphthalein with a cleaning
solution, and the cost of each.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
Question 7: Bobby Bonehead wanted to stick his hand in a large container filled with the following
substances. Describe the feelings or sensations that he will probably feel from each
substance: Do NOT actually do this ever!! Remember, we do not touch chemicals
unless directed by the teacher to do so.
Hydrochloric Acid (HCl): _________________________________________________
Sodium Hydroxide (NaOH): ______________________________________________
A mixed solution with even amounts of HCl and NaOH: ________________________
_____________________________________________________________________
Question 8: In your own words, describe the word neutral. ________________________________
_____________________________________________________________________
_____________________________________________________________________