Acid – Base Neutralization Reactions
Why?
What foods leave you with an upset stomach? Many times upset stomachs result from acidic
foods. In this activity you will explore what is meant by the terms acidic and basic solutions.
Success Criteria:
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Ability to correctly identify solutions as acidic, basic, or neutral.
Ability to model a neutralization reaction.
Prerequisites:
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Ion concentration
Acid/base indicators
Information:
Acid – a compound that yields H+(aq), hydrogen ions (or hydronium ions, H3O+(aq)) as positive ions in
aqueous solution.
Base – a compound that yields OH-1(aq), hydroxide ions as negative ions in aqueous solution.
Neutral solution – contains hydrogen (or hydronium) ions and hydroxide ions in equal concentrations.
Spectator ions – present in acidic and basic solutions, but do not participate in the neutralization
reaction between the H+(aq) (hydrogen ions) and OH-1(aq) (hydroxide ions). Spectator ions can be
positive or negative, and they are present in equal quantities needed to produce electrically neutral
solutions. In other words, there are an equal number of positive and negative ions.
Acid-Base reactions – involves a reaction between an acid and a base. When equal number of moles
of acid (H+ ions) and base (OH-1 ions) react, neutralization occurs.
Model:
Note: spectator ions are not shown in this model, but they are present in each solution.
Key Questions:
1. How does the concentration of H+ compare to the concentration of OH-1 in solution A?
2. How does the concentration of H+ compare to the concentration of OH-1 in solution B?
3. How does the concentration of H+ compare to the concentration of OH-1 in solution C?
4. Identify the acidic solution in the model. How can you tell?
5. Identify the basic solution in the model. How can you tell?
6. Identify the neutral solution in the model. How can you tell?
Exercises:
1. Based upon the information presented in the key of the Model, draw reactants and products
that form when an H+ ion is added to an OH-1 ion.
2. What would happen if solution A and solution B were mixed? Explain your answer.
3. Classify the solution that forms in Exercise 2 as acidic, basic, or neutral and justify your
classification in terms of the concentration of H+ and OH-1 ions.
4. Can a neutral solution contain H+ and/or OH-1 ions? Explain.
5. How many moles of H+ ions are present in one liter of 2 M HCl?
6. How many moles of OH-1 ions are needed to completely neutralize one liter of 2M HCl?
7. How many moles of OH-1 ions are present in one liter of 0.5 M NaOH?
8. How many moles of H+ ions are needed to completely neutralize one liter of 0.5 M NaOH?
©POGIL 2005, 2006; Authored by: Neil Brosnan and Kenneth Levy; Revised by: Kelly Levy
Edited by Linda Padwa and David Hanson, Stony Brook University
pH of Solutions
Why?
What is happening to the pH of the ocean with atmospheric buildup of carbon dioxide? As CO 2
levels in the atmosphere increase, more CO2 dissolves in the ocean causing a change in the ocean’s
hydrogen ion concentration. In this activity you will learn how hydrogen ion concentration is related to
pH.
Success Criteria:
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Ability to calculate the pH of a solution.
Ability to determine if a solution is acidic, basic (alkaline), or neutral.
Ability to compare the relative acidity or hydrogen ion concentrations of various solutions.
Prerequisites:
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Hydrogen ion and hydroxide ion concentrations
Logarithms
Information:
pH – a number used to denote the hydrogen-ion concentration, or acidity, of a solution.
Acidic solution – solution with a pH less than 7, when the concentration of hydrogen ions is greater
than the concentration of hydroxide ions.
Basic solution - solution with a pH greater than 7, when the concentration of hydrogen ions is less than
the concentration of hydroxide ions.
Neutral solution - solution with a pH equal to 7, when the concentration of hydrogen ions is equal to
the concentration of hydroxide ions.
Using the models from page 2, answer the following key questions:
Key Questions:
1. Which solution might have a pH of 5.0? How can you tell?
2. Which solution might have a pH of 7.0? How can you tell?
3. Which solution might have a pH of 10.0? How can you tell?
4. A solution is prepared where 0.10 mole of hydrogen ions and 0.50 mole of hydroxide ions are
added to 200.0 ml of water. Would the solution be acidic, basic, or neutral? Explain.
Exercises:
1. Would the pH of the solution in key question 1, increase, decrease, or not change if 100 mL of
water was added to the solution. Explain.
2. Would the pH of the solution in key question 1, increase, decrease, or not change if hydroxide
ions were added to the solution. Explain.
3. Would the pH of the solution in key question 3, increase, decrease, or not change if hydrogen
ions were added to the solution. Explain.
Further Information:
Calculating pH: pH = -log[H+] where [H+] = molarity of hydrogen ions
Determining [H+] from pH: [H+] = 10-pH
Key Questions:
5. What is the pH of a solution has a [H+] = 1.0 x 10-2?
6. What is the pH of a solution with a [H+] = 1.0 x 10-3?
7. What is the pH of a solution with a [H+] = 1.0 x 10-11
8. What is the [H+] of a solution with a pH of 6.0?
Exercises:
4. How does the pH in key question #6 compare to that in questions #5? Which solution has the
high hydrogen ion concentration? Which solution is more acidic?
5. What is the relationship between the hydrogen ion concentration, [H+], and the pH of a
solution?
6. How many times greater is the hydrogen ion concentration in question #5 than question #6?
This will tell you how many times more acidic solution 5 is than solution 6.
7. New solutions are prepared, solution A has a pH of 4 and solution B has a pH of 7. How many
times more acidic is solution A than solution B?