PH INDICATORS- SONGS LYRICS:
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Crash! That beaker just broke there is solution everywhere.
Dude what’s that solution?
I don’t know, I’m going to touch it.
No! It might not be safe. We gotta test it’s ph.
But how we going do that?
I got just the thang.
CHOURS: Ph indicators...Ph indicators...Gotta use...Ph indicators.
Litmus paper, phenol red, to bromothymol blue. Ph indicators will help you to... Do what it takes to get
the job done. Help you get the concentration of hydronium ions.
The higher the concentration to lower the ph. If the scale is above 7 you know its a base. If its below 7
its got be acidic. Exposure to these could make you very sick, ick.
CHOURS.
Oh I think I’m starting to get what your saying.
No fool! I’m not finished! I gotta finish my song or your knowledge would diminish.
Ah, Ok.
Indicator meets solution, La Chatier’s is in effect. The neutralization or addition of H+ shifts the
equation, to the right or left.
No, No I get it. You Don’t have to rap any more.
But I can still go on about titrations.
No! It’s over.
PH INDICATORS
By: Aaron Ginn & Josh Latka
Dec. 15th, 2009
Chem. 12 ADV
INTRODUCTION
A pH indicator is an organic compound that is added
to a solution to determine its pH visually. The
indicators change color as the pH changes by
detecting the concentration of hydronium ions (H3O+).
PH indicators are frequently used in titrations to
determine the unknown concentration of a known
reactant.
In solution, the indicators establish an equilibrium
between their molecular form (color 1) and their ionic
form (color 2).
SCALES OF COMMON INDICATORS
Indicator
Low pH color
Transition pH range
High pH color
Gentian violet (Methyl violet)
yellow
0.0–2.0
blue-violet
Leucomalachite green (first
transition)
yellow
0.0–2.0
green
Leucomalachite green (second
transition)
green
11.6–14
colorless
Thymol blue (first transition)
red
1.2–2.8
yellow
Thymol blue (second transition)
yellow
8.0–9.6
blue
Methyl yellow
Bromophenol blue
Congo red
Methyl orange
Bromocresol green
Methyl red
red
yellow
blue-violet
red
yellow
red
2.9–4.0
3.0–4.6
3.0–5.0
3.1–4.4
3.8–5.4
4.4–6.2
yellow
purple
red
orange
blue-green
yellow
Methyl red / Bromocresol green
red
4.5–5.2
green
Azolitmin
Bromocresol purple
red
yellow
4.5–8.3
5.2–6.8
blue
purple
Bromothymol blue
Phenol red
Neutral red
Naphtholphthalein
Cresol Red
Phenolphthalein
yellow
yellow
red
colorless to reddish
yellow
colorless
6.0–7.6
6.8–8.4
6.8–8.0
7.3–8.7
7.2–8.8
8.3–10.0
blue
red
yellow
greenish to blue
reddish-purple
fuchsia
Thymolphthalein
colorless
9.3–10.5
blue
Alizarine Yellow R
Litmus
yellow
red
10.2–12.0
4.5-8.3
red
blue
HOW THE WORK
Indicators are present in solutions in two forms, ionized and molecular. Both of these have a distinct color. In
this example of litmus, HLit is the molecule (red) and Lit- is the ion (blue). In solutions, this will establish
equilibrium and depending on the concentration of H+, will change color.
We now use Le Chatelier’s principle to determine what will happen if hydroxide (base) or hydrogen (acid) ions
are added to this equilibrium.
If the concentrations of HLit and Lit - become equal, the color is a mix of the two and the pH at this point is
called the endpoint.
TITRAION CURVES
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Titration is a technique for finding unknown concentration of a known reactant.
An acid-base titration does this through a neutralization reaction where a reactant solution (the titrant)
is dripped into a primary solution (the titrand). One has to be a base and the other an acid.
A titration curve is a graph of the reaction that shows the ph of the titrand solution versus the volume of
titrant added.
There has to be at least a strong base or acid in the titration for it to work properly. The possible
combinations are a strong acid vs a strong base, a weak acid vs a strong base, or a strong acid vs a
weak base.
The equivalent point in a titration is the point at which the number of moles of the unknown solution is
stoichiometrically equal to the number of moles of the titrand solution.
Ph Indicators can be used to visually display the change in ph of the tirand. But certain indicators have
to be kept in mind for their ph scales. For example: If you wanted to find the equivalent point in a strong
acid and base titration, which is about ph of 7, bromothymol blue would be a good choice since its ph
scale is from 6.0 – 7.6.
NATURAL INDICATORS
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Natural ph indicators are indicators found in nature that will change colour
corresponding to a certain ph. The following is a list of natural ph indicators:
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Beets
Blueberries
Carrots
Cherries
Curry Powder
Delphinium Petals
Geranium Petals
Grapes
Horse Chestnut Leaves
Morning Glories
Onion
Pansy Petals
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Petunia Petals
Poison Primrose
Poppy Petals
Purple Peonies
Red cabbage
Red Radish
Rhubarb
Rose Petals
Strawberries
Tea
Thyme
Turmeric
Tulip Petals
Violet Petals
OUR EXPERIMENT: RED CABBAGE PH INDICATOR
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Red Cabbage pH Indicator Colors
ph
2
4
6
8
10
12
Color
Red
Purple
Violet
Blue
BlueGreen
Greenish
Yellow
The pigment molecule flavin is from the Anthocyanins family,
and is in red cabbage. This molecule is an organic
compound that can be used as a ph indicator.
H(flavin)(aq)
H+(aq) + flavin(aq)
BIBLIOGRAPHY
“Acid-Base Indicators.” About.com. 2009. Online. December 12, 2009. http://chemistry.about.com/library/weekly/aa112201a.htm
“Anthocyanins.” Wikipedia. Online. December 12, 2009. <http://en.wikipedia. org/wiki/Anthocyanin>
Clark, Jim. “Acid-Base Indicators.” 2002. Online. December 13, 2009.
http://www.chemguide.co.uk/physical/acidbaseeqia/indicators.html
“pH Indicator.” Wikipedia. Online. December 12, 2009. <http://en.wikipedia. org/wiki/PH_indicator>
“ph indicator.” spiritus-temporis.com. 2005. Online. December 13th, 2009. http://www.spiritus-temporis.com/ph-indicator/naturalph-indicators.html
“pH curves and indicators.” creative-chemistry.org.uk . Online. December 13, 2009. http://www.creativechemistry.org.uk/alevel/module4/documents/N-ch4-05.pdf
“Red Cabbage pH Indicator.” About.com. 2009. Online December 12, 2009. <http://chemistry.about.com/od/acidsbase1/a/redcabbage-ph-indicator.htm>
“Some Common pH Indicators.” 101Science.com. Online. December 13, 2009. http://101science.com/PH.html