measuring ph. what do you need to know? in this section, we have grouped compounds as either...
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![Page 1: Measuring pH. What do you need to know? In this section, we have grouped compounds as either acidic, neutral or basic. Often that is enough information](https://reader036.vdocuments.net/reader036/viewer/2022082710/56649e5e5503460f94b5860a/html5/thumbnails/1.jpg)
Measuring pH
![Page 2: Measuring pH. What do you need to know? In this section, we have grouped compounds as either acidic, neutral or basic. Often that is enough information](https://reader036.vdocuments.net/reader036/viewer/2022082710/56649e5e5503460f94b5860a/html5/thumbnails/2.jpg)
What do you need to know? In this section, we have grouped compounds
as either acidic, neutral or basic. Often that is enough information.
Sometimes a chemist will need to know more specific information, such as the exact pH of the solution.
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What do you need to know? Depending upon what we need to know, we
could make a qualitative or quantitative measurement of pH. Qualitative – Use an indicator to determine if the
solution is an acid, a base or a neutral. Quantitative – Use an indicator or meter to
determine the pH of the solution.
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Indicators An indicator is a chemical that changes colors
as the pH of the solution changes. There are many different indicators that are
used for a variety of reasons. Many of them are just chemicals that are found in nature.
We will focus on three indicators; litmus, phenolphthalein and universal indicator.
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Qualitative Indicator Litmus is a solid that comes from plant
materials. Litmus is typically dissolved in a liquid and
then impregnated on paper. Litmus in an acidic solution is red. Litmus in a basic solution is blue.
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More about Litmus Litmus paper comes in two different types:
Red litmus Blue litmus
If an acid is added to blue litmus, it turns red. If a base is added to blue litmus, it stays blue.
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Phenolphthalein Phenolphthalein is a solid that is dissolved in
a liquid and typically used as a solution. When phenolphthalein is added to a clear
acidic solution, the solution stays clear. When phenolphthalein is added to a clear,
basic solution, the solution turns pink or red.
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PHENOLPHTHALEIN
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Quantitative Measurement Sometimes you want to be more exact and
have the pH of a solution. One choice is to use an electronic pH meter!
Very accurate Can be used with solutions that are not clear Easy to use.
pHydrion paper is another choice.
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Quantitative Indicator pHydrion paper is paper that changes to a
different color when the pH changes. pHydrion paper is paper that has been
impregnated with a mixture of chemicals. Universal indicator is a solution that works
just like pHydrion paper, it changes to a different color with each pH.
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How does pHydrion paper work? Each pH is a different
color. Notice the chart in the picture, pH of 1 is on the left and pH of 14 is on the right.
The colors have the same order as the colors of the rainbow, ROY G. BIV
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Remember: When using litmus paper or pHydrion paper,
only use about a centimeter of paper. If a solution isn’t clear, use a pH meter
because you won’t be able to see the color changes.
Wear your goggles whenever you work with acids or bases.
I before E except after C.