2003 Virginia SOLs
Motivation for Learning
Most carbonated drinks conatin dilute solutions of carbonic and phosphoric acids. Do all such beverages contain the same amount of these acids?
An acid is a substance that produces hydronium ions (H+) in a solution. It is the presence of the H+ ions that gives acids their properties. They taste sour, are electrolytes, are corrosive, and they react with certain compounds or indicators to produce a predictable change in color. An indicator is an organic compound that changes color in an acid or a base.
A base is a substance that produces hydroxide ions (OH-) in solution. Bases feel slippery and have a bitter taste, are corrosive, are electrolytes, and also react with indicators to produce a predictable change in color.
Neutralization is a chemical reaction between an acid and a base. During a neutralization reaction, hydronium ions from the acid combine with the hydroxide ions from the base to form water.
H3 O + (aq) + OH- (aq) --> H2O (l)
The hydroxide ions present in all basic solutions are negative ions, whereas the hydronium ions in acidic solutions are positive ions. As the reactive hyrdonium and hydroxide ions are removed from the solution, the acidic and basic properties of the reactants are cancelled, or neutralized.
In the student activity, be sure to mix the contents well after each drop of NaOH is added. If not mixed, the acid may be neutralized at the top, giving a false result. If small Erlenmyer flasks are available they will work better than test tubes. The pink color can best be seen if the flasks are sitting on a piece of white paper. For most carbonated beverages, approximately 5 mL of soda requires 15 - 25 drops of NaOH solution. Be sure to try this activity ahead of time to make sure that the two beverages chosen have a measurable difference in acidity. There are many clear, carbonated soft drinks that will work. You can also do this activity with more than 2 types of soda.
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|Sample||Kind of Soda||# of drops of NaOH|
Write out the balanced chemical equation for the reaction between NaOH and carbonic acid, H 2 CO 3 . If additional water were added to the NaOH solution, how would it affect the number of drops required for neutralization?
Also see graphing calculator-based activity for determining the pH of a substance.
Students with Special Needs
All students should be able to participate in this activity.
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Answers to Assessment