Acid-base indicator

In acid-base titration, the sudden change in color of acid-base indicator is used to indicate the end point of titration. Acid-base indicator usually is a weak organic acid or an organic weak base. In alkaline solution, the indicator lost protons that it changes from the acid to basic (expressed in In-), and give protons in acidic solution changing from the basic to acid (expressed in HIn), accompanied by changes of structure and color. Since the equilibrium constants KHlπ are different from variety of indicators, the color range is different. Some discoloration happens in an acidic solution, some happens in the vicinity of neutral, some discoloration occurs in an alkaline solution. Thus, you can select the appropriate acid-base indicator based on acid-base titration equivalence point of pH value and the jump range. For example, strong base titrate weak acid, etc. the solution appear weak alkaline at the titration endpoint, pH leap is also included in the alkaline range near the titration endpoint, and the choice of thymol blue or phenolphthalein indicator is correct, while the methyl orange which change color in an acidic solution is not proper. On the contract, strong acid weak base titration, the solution appear weak acidic at the titration endpoint, pH leap is also included in the acidic range near the titration endpoint. The choice of methyl red, methyl orange and bromine cresol green indicator are very appropriate.

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Structure Chemical Name CAS MF
Bismuththiol Bismuththiol 1072-71-5 C2H2N2S3
1,10-Phenanthroline hydrate 1,10-Phenanthroline hydrate 5144-89-8 C12H10N2O
Cresol Purple Cresol Purple 2303-01-7 C21H18O5S
Methyl Red sodium salt Methyl Red sodium salt 845-10-3 C15H15N3O2
2,6-DINITROPHENOL 2,6-DINITROPHENOL 573-56-8 C6H4N2O5
BCP BCP 62625-30-3 C21H15Br2NaO5S
ALIZARIN COMPLEXONE ALIZARIN COMPLEXONE 3952-78-1 C19H15NO8
ROSOLIC ACID ROSOLIC ACID 603-45-2 C19H14O3
alpha-Naphtholphthalein alpha-Naphtholphthalein 596-01-0 C28H18O4
Mordant Orange 1 Mordant Orange 1 2243-76-7 C13H9N3O5
Methyl Red Methyl Red 493-52-7 C15H15N3O2
Tetrabromophenol Blue Tetrabromophenol Blue 4430-25-5 C19H7Br8O5S
METHYL PURPLE METHYL PURPLE 1340-02-9 C67H62N8Na4O14S3
4-(2-PYRIDYLAZO)RESORCINOL 4-(2-PYRIDYLAZO)RESORCINOL 1141-59-9 C11H9N3O2
4-(4-ETHOXYPHENYLAZO)-M-PHENYLENEDIAMINE MONOHYDROCHLORIDE 4-(4-ETHOXYPHENYLAZO)-M-PHENYLENEDIAMINE MONOHYDROCHLORIDE 2313-87-3 C14H17ClN4O
α-Naphthoflavone α-Naphthoflavone 604-59-1 C19H12O2
N,N'-Diphenylbenzidine N,N'-Diphenylbenzidine 531-91-9 C24H20N2
Sodium 2-nitrophenoxide Sodium 2-nitrophenoxide 824-39-5 C6H4NNaO3
LACMOID LACMOID 42249-61-6 C12H6Br4N2O3
M-CRESOL PURPLE, SODIUM SALT M-CRESOL PURPLE, SODIUM SALT 62625-31-4 C21H17NaO5S
PHENOLPHTHALEIN DISODIUM SALT PHENOLPHTHALEIN DISODIUM SALT 518-51-4 C20H12Na2O4
BUFFER SOLUTION PH 7.00 BUFFER SOLUTION PH 7.00
Chlorophenol Red Chlorophenol Red 4430-20-0 C19H12Cl2O5S
Pigment Blue 61 Pigment Blue 61 1324-76-1 C37H29N3O3S
3-Nitrophenol 3-Nitrophenol 554-84-7 C6H5NO3
2-Nitrophenol 2-Nitrophenol 88-75-5 C6H5NO3
3,8-Dibromophenanthroline 3,8-Dibromophenanthroline 100125-12-0 C12H8Br2N2
LITMUS LITMUS 1393-92-6 n.a.
CI NO 52015 CI NO 52015 97130-83-1 C32H38Cl4N6OS2Zn
Curcumin Curcumin 458-37-7 C21H20O6
ZINCON ZINCON 135-52-4 C20H16N4O6S
TETRABROMOPHENOLPHTHALEIN ETHYL ESTER POTASSIUM SALT TETRABROMOPHENOLPHTHALEIN ETHYL ESTER POTASSIUM SALT 62637-91-6 C22H13Br4KO4
CYANINE CYANINE 523-42-2 C29H35IN2
o-Phenanthroline o-Phenanthroline 66-71-7 C12H8N2
ALLOXAN TETRAHYDRATE ALLOXAN TETRAHYDRATE 6010-91-9 C4H10N2O8
Mordant Yellow 1 Mordant Yellow 1 584-42-9 C13H8N3NaO5
p-Naphtholbenzein p-Naphtholbenzein 145-50-6 C27H18O2
IODIDE-STARCH SOLUTION IODIDE-STARCH SOLUTION 9010-71-3
2,2'-Bipyridine 2,2'-Bipyridine 366-18-7 C10H8N2
Buffer solution, pH 7.00 (^+0.01 @ 25^oC), Colored Yellow, Specpure|r, NIST Traceable Buffer solution, pH 7.00 (^+0.01 @ 25^oC), Colored Yellow, Specpure|r, NIST Traceable
Thymolphthalein Thymolphthalein 125-20-2 C28H30O4
Acid modified starch Acid modified starch 68412-29-3 (C6H10O5)n
2-Nitroaniline 2-Nitroaniline 88-74-4 C6H6N2O2
2,5-DINITROPHENOL 2,5-DINITROPHENOL 329-71-5 C6H4N2O5
o-Cresolphthalein o-Cresolphthalein 596-27-0 C22H18O4
SULFONAZO 3 SULFONAZO 3 1738-02-9 C22H16N4O14S4
METHYLENE BLUE METHYLENE BLUE 122965-43-9 C16H20ClN3OS
BIS(2,4-DINITROPHENYL)ACETIC ACID ETHYL ESTER BIS(2,4-DINITROPHENYL)ACETIC ACID ETHYL ESTER 5833-18-1 C16H12N4O10
LACMOID LACMOID 33869-21-5 C12H6Br4N2O3
BENZYL ORANGE BENZYL ORANGE 36402-77-4 C19H16N3NaO3S
1,3,5-TRINITROBENZENE 1,3,5-TRINITROBENZENE 99-35-4 C6H3N3O6
BROMOCRESOL GREEN - METHYL RED SOLUTION (ETHANOL SOLN.)[MIXED INDICATOR] BROMOCRESOL GREEN - METHYL RED SOLUTION (ETHANOL SOLN.)[MIXED INDICATOR]
ARSENAZO III ARSENAZO III 1668-00-4 C22H18As2N4O14S2
PENTAMETHOXY RED PENTAMETHOXY RED 1755-51-7 C24H26O6
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