Lab 11: ANTACID ANALYSIS- INTRODUCTION TO NEUTRALIZATION REACTIONS
- Page ID
- 506042
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)PURPOSE
The purpose of this experiment is to:
• Perform a microscale acid-base neutralization reaction.
• Observe the behavior of an indicator in acidic and basic solutions.
• Determine the effectiveness of a name brand and generic brand antacid in relation to each other.
INTRODUCTION
Neutralization occurs when an equal amount of acid reacts with an equal amount of base to produce water and a salt, as shown below:
HCl (aq) + NaOH (aq) → H2O (l) + NaCl (aq)
Recall from previous lectures that we defined an acid as a substance that produces hydrogen ions when dissolved in water. Bases produce hydroxide ions when dissolved in water. In future chemistry classes, you will go into more detail about these reactions and the concept of neutralization. In this experiment, we will be applying the concept of acid-base neutralization to antacids, substances that counteract excess acid (HCl) in the stomach to relieve indigestion and heartburn. The active ingredient in many antacids is calcium carbonate, which reacts with excess HCl, as follows:
CaCO3 (s) + 2 HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l)
First, the antacid will be dissolved in HCl solution and react according to the above equation. This process will amount to consuming an antacid tablet to relieve an upset stomach. However, after the reaction is complete, excess HCl will remain in solution. The amount of HCl remaining will be determined by reacting it with NaOH in the presence of phenolphthalein, an indicator that is colorless in acidic solution and pink in basic solutions. The less HCl remaining in solution (or the fewer drops of NaOH required to complete neutralization) indicates the greater effectiveness of the antacid. Consider the following example:
An antacid was dissolved in HCl solution, and 20 drops of this solution were then transferred to a well plate. Two drops of phenolphthalein indicator were added to the well, resulting in a colorless solution. NaOH was then added drop wise to the well. After the addition of five drops of NaOH, the solution remained a faint pink color. Based on this information:
1) It took 5 drops of NaOH to react with the excess acid.
2) This means the antacid neutralized 15 drops of the acid (20-5).
When comparing two antacids, the one that requires fewer drops of NaOH to complete neutralization will be identified as the more effective antacid. During this experiment, you will be comparing the effectiveness of a name-brand antacid with a generic antacid.
SAFETY PRECAUTIONS
1) Always wear chemical splash goggles while working with chemicals in this experiment.
2) Handle all chemicals with care.
3) Follow all the clean-up instructions as provided by your instructor.
EQUIPMENT* AND CHEMICALS NEEDED
• Mortar and pestle
• Three disposable plastic droppers
• Well plate
• 50 mL beaker
• 600 mL beaker
• Stirring rod
• Two 250 mL Erlenmeyer flasks
• Name brand antacid
• Generic brand antacid
• 0.5 M HCl
• Phenolphthalein indicator
• 0.5 M NaOH
• Non-halogenated organic waste container
• Inorganic waste container
* Images of equipment needed in this lab can be found in the appendix (the equipment may differ or be subject to changes; follow your instructors’ directions).
EXPERIMENTAL PROCEDURE
1) Before beginning the experiment, prepare the relieved upset stomach solutions. It would be best if the instructor or lab assistant did this. Using a mortar and pestle, crush a name-brand antacid tablet (or tablets) amounting to 500 mg of active ingredient. Transfer the crushed tablet to a 250 mL Erlenmeyer flask and add 30 mL of 0.5 M HCl. Make sure the antacid tablet is dissolved as best as possible. This solution can then be transferred to a reagent bottle labeled “name-brand antacid solution.”
2) Repeat step 1 using a generic brand antacid tablet. The solution can then be transferred to a reagent bottle labeled “generic antacid solution.”
3) Obtain a well plate. Using a disposable plastic dropper, transfer 20 drops of the name-brand antacid solution to three wells. (Note: Be sure that the number of drops transferred to each well is as accurate as possible. It is best to transfer the drops slowly, one at a time, while holding the dropper straight up and not angled. You may also want to count aloud as you add the drops.)
4) Add 2 drops of phenolphthalein indicator to each well.
5) Quarter-fill a 50 mL beaker with 0.5 M NaOH solution. Using a disposable plastic dropper (the same size as the one used in Step 3), add the NaOH solution drop wise to the first well. Use a stirring rod to stir the solution between each drop added. Continue this process until a faint pink color remains without disappearing. Record, in the data table, the number of drops of NaOH required to complete neutralization.
6) Repeat Step 5 with the remaining two wells.
7) Repeat Steps 3-6 with the generic brand of the antacid solution.
8) Pour the contents of the well plate into a 600 mL beaker and pour the solution in the beaker into the non-halogenated organic waste container.
9) Pour the excess NaOH into the inorganic waste container.
10) Dispose of the used droppers into the appropriate container or as directed by your instructor.
11) Clean your work area and all glassware before leaving the lab and return all equipment to the appropriate place.
PRE-LAB QUESTIONS Name ____________________________________
1) Briefly explain how antacid is used to relieve an upset stomach.
2) What is the purpose of using phenolphthalein indicator in this experiment?
3) 20 drops of a relieved upset stomach solution were transferred into a well plate. Two drops of phenolphthalein indicator were added. It was shown that 8 drops of NaOH were required to turn the solution to a permanent faint pink color. How many drops of acid were neutralized by the antacid?
4) Imagine the experiment described in pre-lab question 3 was repeated using another antacid. This antacid required 6 drops of NaOH to complete neutralization. Based on the results of this experiment, would this antacid be more effective or less effective than the antacid used in question 3? Explain.
DATA AND OBSERVATIONS
Name-brand antacid used:
Active ingredient:
|
Name brand Antacid |
Trial 1 |
Trail 2 |
Trial 3 |
|
Drops of relieved upset stomach solution added to well |
20 |
20 |
20 |
|
Drops of NaOH required to complete neutralization |
|||
|
Drops of acid neutralized by antacid |
Average drops of acid neutralized by name-brand Antacid:
______________________________________________________________________________
Generic brand Antacid:
Active ingredient:
|
Generic brand Antacid |
Trial 1 |
Trial 2 |
Trial 3 |
|
Drops of relieved upset stomach solution added to well |
20 |
20 |
20 |
|
Drops of NaOH required to complete neutralization |
|||
|
Drops of acid neutralized by antacid |
Average drops of acid neutralized by generic antacid:
POST LAB QUESTIONS
1) Based on the results of this experiment, which antacid was more effective? Explain.
2) How do your results compare with those of your classmates?
3) What are some sources of error in this experiment?
4) How accurate do you feel this experiment was in determining the effectiveness of the two antacid brands? Explain.
5) Look up the cost of each antacid. Based on the cost and results of this experiment, which antacid do you feel is a better buy?
6) Were the active ingredients in each antacid the same? If yes, why would one antacid show different results than the other?