News
Forum
Lessons
Printouts
Experiment
Utilities
Contact
Molecule of the Week
About
Arginine

NaOH + HCl

Introduction

This experiment is designed to teach the experimenter about the properties of an acid-base reaction, a special type of double replacement reaction.

Sodium hydroxide (NaOH) and hydrochloric acid (HCl) are cheap and readily available and are the classic laboratory examples of a base and acid, respectively.  Both have extreme pH values (NaOH is one of the strongest bases known).  These properties make them ideal for an acid-base reaction demonstration.

WARNING AND DISCLAIMER

Though the chemicals used in this experiment are somewhat dilute in the procedure, they are acids and bases nonetheless.  A potential for burns exists especially if the experimenter must dilute the acid to the appropriate strength.  Remember, if diluting, ALWAYS add acid to water, NEVER the other way around.  Of course, one must be very careful when adding the solid sodium hydroxide to water, for the solid sodium hydroxide can easily damage tissues.  This said, the usual disclaimer applies:

The International Order of Nitrogen, its officers, and/or its members are not responsible for your actions.  Carry this out at your own risk.

Read the entire procedure TWICE before starting the experiment!

Reaction In Summary

NaOH (aq) + HCl (aq) --> NaCl (aq) + H2O (l)

Facilities

To do this experiment safely, you will need to have ready access to the following:

  • Water supply
  • Eye wash station
  • Emergency shower

Supplies and Equipment

The following are listed in the order they will be used.

  • Two 50 mL laboratory beakers
  • 25 mL 4 M hydrochloric acid
  • 25 mL distilled water
  • 4 g sodium hydroxide (pellet or powder)
  • One glass stirring rod
  • Wide range pH indicator solution (amount depends on kind)
  • One 100 mL laboratory beaker

Procedure

Before going any further, be sure to have read the warning and disclaimer.

Solid sodium hydroxide is an extremely strong base.  Avoid contact with skin.  If contact occurs, flush with a weak acid, such as acetic acid (vinegar).  This will neutralize the base.  If eye contact occurs, use the eye wash station and seek prompt medical attention.  Use the emergency shower if a large portion of the body is contacted, and seek immediate medical attention.  Dilute all spills with a weak acid and clean up as soon as possible.

Hydrochloric acid is a strong acid.  The procedure calls for a relatively dilute (4 M) solution, though even this can present a danger, especially if the dilute solution must be manually prepared from a stronger solution.  Avoid contact with skin.  If contact occurs, douse with a weak base, such as sodium bicarbonate (baking soda).  This will neutralize the acid.  If eye contact occurs, use the eye wash station and seek prompt medical attention.  Use the emergency shower if a large portion of the body is contacted, and seek immediate medical attention.  Dilute all spills with a weak base and clean up as soon as possible.

  1. Pour the hydrochloric acid into a 50 mL beaker.
  2. Pour the water into a 50 mL beaker.
  3. Carefully add the sodium hydroxide to the water and stir with the stirring rod until dissolved.
  4. Add a sufficient amount of indicator solution to each beaker so as to allow the pH to be determined.
  5. Record observations.
  6. Carefully pour the contents of one of the beakers into the 100 mL beaker.
  7. Carefully (and very slowly) pour the contents of the other 50 mL beaker into the 100 mL beaker.
  8. Record observations.
  9. Stir with the stirring rod and record any new observations.
  10. Flush the contents down the sink with water (unless otherwise directed by the lab director).

What's Happening

By adding the sodium hydroxide to the water, a 4 M solution of sodium hydroxide was created.  The universal indicator solution changes color based on the pH of the solution it is placed in.  This allowed the pH of the acid and base to be roughly determined.  When the solutions of acid and base were mixed, a double replacement reaction occurred, resulting in sodium chloride (NaCl), a salt, and water (H2O).  Sodium chloride, the sodium salt produced in this reaction, is more commonly known as table salt.  Salts are pH neutral, as is water.  This is why the indicator suddenly showed a neutral pH upon combining the solution.

Questions

If you fully understand what's happening in this reaction, see if you can answer the following questions for yourself:

  1. Why was a 4 M solution, not some other concentration, of sodium hydroxide made for this experiment?
  2. How would the reaction differ if no indicator solution were used?  Why?
  3. If the water were boiled off at the end of the experiment, what would be left?
  4. Predict the results of the addition of ammonia (NH3), a base, to aqueous hydrogen fluoride (HF), a very strong acid. Is this a typical acid-base reaction (hint: consider water)?
  5. What is a generalized definition of a salt?

Author: C. Shultz

Page may be printed for personal or classroom reference. For full usage information, please read our Terms of Usage.