Acid-Base Indicators. Measuring pH Now that we know how to calculate pH of a solution, how do we...
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Transcript of Acid-Base Indicators. Measuring pH Now that we know how to calculate pH of a solution, how do we...
![Page 1: Acid-Base Indicators. Measuring pH Now that we know how to calculate pH of a solution, how do we measure it in the lab? – The following slides will provide.](https://reader036.fdocuments.in/reader036/viewer/2022082411/56649da75503460f94a934f6/html5/thumbnails/1.jpg)
Acid-Base Indicators
![Page 2: Acid-Base Indicators. Measuring pH Now that we know how to calculate pH of a solution, how do we measure it in the lab? – The following slides will provide.](https://reader036.fdocuments.in/reader036/viewer/2022082411/56649da75503460f94a934f6/html5/thumbnails/2.jpg)
Measuring pH
• Now that we know how to calculate pH of a solution, how do we measure it in the lab?– The following slides will provide numerous
examples of ways to measure pH in the laboratory.
![Page 3: Acid-Base Indicators. Measuring pH Now that we know how to calculate pH of a solution, how do we measure it in the lab? – The following slides will provide.](https://reader036.fdocuments.in/reader036/viewer/2022082411/56649da75503460f94a934f6/html5/thumbnails/3.jpg)
pH testing• There are several ways to test pHThere are several ways to test pH– Blue litmus paper (red = acid)Blue litmus paper (red = acid)– Red litmus paper (blue = basic)Red litmus paper (blue = basic)– pH paper (multi-colored)pH paper (multi-colored)– pH meter (7 is neutral, <7 acid, >7 base)pH meter (7 is neutral, <7 acid, >7 base)– Universal indicator (multi-colored)Universal indicator (multi-colored)– Indicators like phenolphthaleinIndicators like phenolphthalein– Natural indicators like red cabbage, Natural indicators like red cabbage,
radishesradishes
![Page 4: Acid-Base Indicators. Measuring pH Now that we know how to calculate pH of a solution, how do we measure it in the lab? – The following slides will provide.](https://reader036.fdocuments.in/reader036/viewer/2022082411/56649da75503460f94a934f6/html5/thumbnails/4.jpg)
Paper testing• Paper tests like litmus paper Paper tests like litmus paper
and pH paperand pH paper– Put a stirring rod into the solution and Put a stirring rod into the solution and
stir.stir.– Take the stirring rod out, and place a Take the stirring rod out, and place a
drop of the solution from the end of drop of the solution from the end of the stirring rod onto a piece of the the stirring rod onto a piece of the paperpaper
– Read and record the color change. Read and record the color change. Note what the color indicates.Note what the color indicates.
– You should only use a small portion of You should only use a small portion of the paper. You can use one piece of the paper. You can use one piece of paper for several tests.paper for several tests.
![Page 5: Acid-Base Indicators. Measuring pH Now that we know how to calculate pH of a solution, how do we measure it in the lab? – The following slides will provide.](https://reader036.fdocuments.in/reader036/viewer/2022082411/56649da75503460f94a934f6/html5/thumbnails/5.jpg)
pH paperpH paper
![Page 6: Acid-Base Indicators. Measuring pH Now that we know how to calculate pH of a solution, how do we measure it in the lab? – The following slides will provide.](https://reader036.fdocuments.in/reader036/viewer/2022082411/56649da75503460f94a934f6/html5/thumbnails/6.jpg)
pH meter
• Tests the voltage of the Tests the voltage of the electrolyteelectrolyte
• Converts the voltage to pHConverts the voltage to pH• Very cheap, accurateVery cheap, accurate• Must be calibrated with a Must be calibrated with a
buffer solutionbuffer solution
![Page 7: Acid-Base Indicators. Measuring pH Now that we know how to calculate pH of a solution, how do we measure it in the lab? – The following slides will provide.](https://reader036.fdocuments.in/reader036/viewer/2022082411/56649da75503460f94a934f6/html5/thumbnails/7.jpg)
pH indicators• Indicators are dyes that can be added that
will change color in the presence of an acid or base.
• Most are large molecules that act as weak acids. The color changes occur when the molecules is ionized (acting as an acid) or un-ionized (acting as a base).
• Some indicators only work in a specific range of pH. Choosing the right one is important!
• Once the drops are added, the sample is ruined
• Some dyes are natural, like radish skin or red cabbage
![Page 8: Acid-Base Indicators. Measuring pH Now that we know how to calculate pH of a solution, how do we measure it in the lab? – The following slides will provide.](https://reader036.fdocuments.in/reader036/viewer/2022082411/56649da75503460f94a934f6/html5/thumbnails/8.jpg)
Choosing the Correct Indicator
• Not all indicators shift colors at pH 7. • Many change colors over a wide range of pH
values.• When testing a sample for acidity or basicity it
is best to choose an indicator that has a color change close to pH 7 – Or use pH paper– Or use a pH meter to get a digital reading
![Page 9: Acid-Base Indicators. Measuring pH Now that we know how to calculate pH of a solution, how do we measure it in the lab? – The following slides will provide.](https://reader036.fdocuments.in/reader036/viewer/2022082411/56649da75503460f94a934f6/html5/thumbnails/9.jpg)
Sample Indicator pH Ranges• Crystal Violet = yellow (pH 1) blue• Cresol Red = red (pH 2) yellow (pH 8) red• Thymol Blue = red (pH 3) yellow (pH 8) green/blue• Bromophenol blue = yellow (pH 4) blue• Methyl orange = red (pH 4.5) orange/yellow• Bromcresol green = yellow (pH 4.5) green/blue• Methyl red = pink (pH 5.5) yellow• Bromcresol purple = yellow (pH 6) purple• Alizarin = yellow (pH 6.5) red (pH 12) purple• Bromthymol blue = yellow (pH 7 ) green/blue• Phenol red = yellow (pH 7.2) red• Phenolpthalein = clear (pH 8.3) pink• Thymolphtalien = clear (pH 10) blue• Alizarin yellow GG = orange (pH 10.5) red• Universal Indicator = red (pH 4) orange (pH 6) yellow (pH 7) green (pH 8) blue (pH
9) purple