Experiment_624_Measuring pH_1_2
- Page ID
- 305606
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)
( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\id}{\mathrm{id}}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\kernel}{\mathrm{null}\,}\)
\( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\)
\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\)
\( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)
\( \newcommand{\vectorA}[1]{\vec{#1}} % arrow\)
\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}} % arrow\)
\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vectorC}[1]{\textbf{#1}} \)
\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)
\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)
\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)
Student Name |
|
Laboratory Date: Date Report Submitted: |
___________________________
|
Student ID |
|
Experiment Number and Title |
Experiment 624: Measuring pH
|
Experiment 624: Measuring pH
Section 1: Purpose and Summary
-
Determine the pH of some solutions using ‘red cabbage’ indicator.
-
Determine the pH of solutions using a pH meter.
-
Understand the effect of adding an acid or a base to buffer solutions.
In this experiment, the instructor will prepare a pH indicator by extracting colored substances from red cabbage. This pH indicator solution will be added to buffer solutions of pH range 1 – 13. Students will record the resultant color of each buffer solution. Students will then use the indicator to determine the pH of common solutions by comparing the color to the buffers. To measure the exact pH values of solutions, a laboratory pH meter will be used. Students will determine the hydrogen ion concentration, [H+] of the solutions from the pH value recorded. Students will determine the effect of adding HCl or NaOH to an acetic acid/acetate buffer solution.
Section 2: Safety Precautions and Waste Disposal
Safety Precautions:
Use of eye protection is recommended for all experimental procedures.
Waste Disposal:
All reagents used in this experiment are generally non-toxic and may be disposed of in sinks with tap water rinses.
Section 3: Procedure
Part 1: Preparing the pH indicator and pH standards – INSTRUCTOR DEMO
NOTE: Part 1 may be replaced by the use of universal indicating solution at the instructor’s option.
|
|
|
|
Buffer pH |
Color with Cabbage Indicator |
1 |
|
2 |
|
3 |
|
4 |
|
5 |
|
6 |
|
7 |
|
8 |
|
9 |
|
10 |
|
11 |
|
12 |
|
13 |
|
Part 2: pH determination of household products or everyday chemicals
Possible household items: white vinegar, colorless soda like SpriteTM, dish soap solution (colorless), sparkling water, alkaline water, isopropyl alcohol
Everyday chemicals: 0.1 M HCl, 0.1 M acetic acid, 0.1 M ammonia, 0.1 M NaOH
|
|
|
|
|
|
Solutions tested |
Approximate pH |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Part 3: Quantitative determination of pH
This procedure describes how to use a portable Flinn pH meter (model AP8673). If the pH meter is not measuring properly (unstable, or inaccurate), refer to the manual for troubleshooting.
|
|
|
|
|
|
|
|
|
Solutions tested |
pH |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Part 4: Effect of adding an acid or a base to the pH of a buffer
|
|
|
|
|
|
Solutions tested |
pH |
pH after addition of 0.1 M HCl |
A (laboratory water) |
|
|
B (buffer solution) |
|
|
Solutions tested |
pH |
pH after addition of 0.1 M NaOH |
C (laboratory water) |
|
|
D (buffer solution) |
|
|
Post Lab Questions:
-
Based on your results, classify each test solution as acidic, basic, or neutral.
-
Write the mathematical equation that shows the relationship between pH value and the hydrogen ion concentration, [H+]. What is the unit of [H+]?
-
Using your results in Part 3 of this experiment, calculate [H+] for each test solution. Include units.
-
Compare a solution with pH 10.5 and a solution with pH 4.5. Which solution contains more H+ ions? Explain.
-
Two methods were used in determining the pH of the solutions – pH paper and pH meter. Do they show similar or different pH values? What was different?
-
Compare the pH of the buffer solutions in Part 4 of this experiment before and after the addition of 0.1 M HCl and 0.1 M NaOH. Does this confirm the expected behavior of a buffer solution against an added acid or base? Explain.