 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.

By: Aaron Ginn & Josh Latka Dec. 15 th, 2009 Chem. 12 ADV

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 (H 3 O + ). 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).

IndicatorLow pH colorTransition pH rangeHigh pH color Gentian violet (Methyl violet)yellow0.0–2.0blue-violet Leucomalachite green (first transition) yellow0.0–2.0green Leucomalachite green (second transition) green11.6–14colorless Thymol blue (first transition)red1.2–2.8yellow Thymol blue (second transition)yellow8.0–9.6blue Methyl yellowred2.9–4.0yellow Bromophenol blueyellow3.0–4.6purple Congo redblue-violet3.0–5.0red Methyl orangered3.1–4.4orange Bromocresol greenyellow3.8–5.4blue-green Methyl redred4.4–6.2yellow Methyl red / Bromocresol greenred4.5–5.2green Azolitminred4.5–8.3blue Bromocresol purpleyellow5.2–6.8purple Bromothymol blueyellow6.0–7.6blue Phenol redyellow6.8–8.4red Neutral redred6.8–8.0yellow Naphtholphthaleincolorless to reddish7.3–8.7greenish to blue Cresol Redyellow7.2–8.8reddish-purple Phenolphthaleincolorless8.3–10.0fuchsia Thymolphthaleincolorless9.3–10.5blue Alizarine Yellow Ryellow10.2–12.0red Litmusred blue

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.

 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 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:  Beets  Blueberries  Carrots  Cherries  Curry Powder  Delphinium Petals  Geranium Petals  Grapes  Horse Chestnut Leaves  Morning Glories  Onion  Pansy Petals  Petunia Petals  Poison Primrose  Poppy Petals  Purple Peonies  Red cabbage  Red Radish  Rhubarb  Rose Petals  Strawberries  Tea  Thyme  Turmeric  Tulip Petals  Violet Petals

 Red Cabbage pH Indicator Colors ph ColorRedPurpleViolet BlueBlue- Green 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)

“Acid-Base Indicators.” About.com Online. December 12, “Anthocyanins.” Wikipedia. Online. December 12, Clark, Jim. “Acid-Base Indicators.” Online. December 13, “pH Indicator.” Wikipedia. Online. December 12, “ph indicator.” spiritus-temporis.com Online. December 13 th, ph-indicators.html “pH curves and indicators.” creative-chemistry.org.uk. Online. December 13, chemistry.org.uk/alevel/module4/documents/N-ch4-05.pdf “Red Cabbage pH Indicator.” About.com Online December 12, “Some Common pH Indicators.” 101Science.com. Online. December 13,