LAB 8: INTRODUCTION TO ACIDS AND BASES
- Page ID
- 506009
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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
• Determine the pH of various solutions.
• Examine how pH affects litmus paper and red cabbage indicator.
• Identify solutions as acidic, basic, or neutral.
INTRODUCTION
pH is a measure of the hydrogen ion concentration in a solution. We can use pH values to identify whether a solution is acidic, basic, or neutral. The pH scale ranges from 0-14. Acidic solutions have a pH of less than 7, neutral solutions have a pH of 7, and basic solutions have a pH greater than 7.
In this experiment, we will first use litmus paper to determine whether a solution is acidic or basic. We will then use pH paper and a pH meter to measure the pH of the solution. Finally, we will explore the effect of pH on the red cabbage indicator, which changes colors at various pH levels.
SAFETY PRECAUTIONS
1) Always wear chemical splash goggles when working on this experiment.
2) Gloves are provided, should you wish to use them.
3) Dispose of all waste, as indicated by your instructor.
4) Thoroughly clean your work area when finished and return all equipment and chemicals to their appropriate place.
EQUIPMENT AND CHEMICALS NEEDED
• Well plate
• pH meter
• Deionized water in a water bottle
• Red litmus paper
• Blue litmus paper
• pH paper
• Kimwipes
• Stirring rod
• Red cabbage indicator
• Tap water
• 0.5 M - 1 M solutions of vinegar, baking soda, bleach, detergent, ammonia
• Soft drink
• Glass cleaner
• Rubbing alcohol
* Images of equipment needed in this lab can be found in the appendix (the equipment may differ a little or be subject to changes, follow your instructors’ directions).
EXPERIMENTAL PROCEDURE
1) Obtain a well plate and add 10 drops of each solution listed in the equipment needed section (or refer to the data table) to individual wells.
2) Determine what color each solution turns the red litmus paper. To do this, dip the end of a strip of paper into the solution in the first well. To avoid wasting the litmus paper, tear off the part that was previously used and dip the remaining end into the next solution. Repeat this process for each solution. (You can likely test 3-4 solutions with a single strip of litmus paper.). In the data table, record what color the solutions turn the red litmus paper.
3) Repeat step 2 using blue litmus paper.
4) Repeat step 2 using pH paper. In this case, you could match the color of each solution turning the pH paper to the pH chart provided with the pH paper.
5) Determine the pH of each solution using a pH meter. Depending on the pH meter you use, specific instructions may be available. Consult your instructor for more information. Rinse the pH probe between solutions with deionized water, then gently pat dry it with a Kim wipe before immersing it in the next solution.
6) Add 2-3 drops of red cabbage indicator to each solution. Stir each solution with a stirring rod (rinsing and wiping the stirring rod between solutions), and record in the data table the color each solution turns.
7) Pour the contents of the well plate into the sink and rinse with plenty of water.
8) Thoroughly wash all glassware with soap and water and return all equipment and chemicals to the appropriate place. Clean your work area before leaving the lab.
PRE-LAB QUESTIONS Name ____________________________________
1) What color does red litmus paper turn in acidic and basic solutions?
2) What color does blue litmus paper turn in acidic and basic solutions?
3) List three properties of acids.
4) List three properties of bases.
5) What is an indicator? How can it be used to detect changes in the pH levels of solutions?
DATA AND OBSERVATIONS
Complete the following table. In the column headed “Color red litmus paper turns,” “Color blue litmus paper turns,” and “Color solution turns with red cabbage indicator,” record the color observed. Under pH paper and pH meter, record the pH value.
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Color Change of Red Litmus Paper |
Color Change of Blue Litmus Paper |
pH value from pH paper |
pH value from pH meter |
Color Change with Red Cabbage Indicator |
Is the solution acidic, basic, or neutral? |
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Tap water. |
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Deionized water |
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Vinegar |
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Baking soda |
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Bleach |
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Detergent |
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Ammonia |
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Soft drink |
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Glass cleaner |
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Rubbing alcohol |
POST-LAB QUESTIONS
1) Rank the following (litmus paper, pH paper, pH meter, red cabbage indicator) from least to most accurate in determining the pH value of a solution.
2) What color does the red cabbage indicator turn in acidic solutions?
3) What color does the red cabbage indicator turn in basic solutions?
4) Which tests (litmus paper, pH paper, pH meter, red cabbage indicator) were used to determine whether the solution was acidic, basic, or neutral?
5) Did any of the test results surprise you? If yes, which ones, and why?
6) Provide three examples of acids and three examples of bases used in everyday life that were not explored in this experiment.