Indicator

indicator係用黎測試一個化學反應既end point~
又或者測試一個物量既存在~
例如acid-base indicator~
可以用黎測試中和作用既中和點~
因為indicator有好大既顏色轉變比你睇~你就知道個化學反應既中和點到左未~
有時用黎測試物質既存在~
例如用hydrogen carbonate indicator~可以測試二氧化碳既存在~

可能仲有其他用途~我知既係咁多~

An indicator is a chemical substance that is used in titration to indicate the equivalence point. It is either a weak base or a weak acid. When undissociated, the indicator is one color, but at and after equivalence point, the indicator dissociates and becomes a different color.

HIn (aq) <--> H+(aq) + In- (aq)
Color A Color B
(color in acid solution) ( color in alkali solution)

When using an indicator, it is best to use one that has a pH range that the equivalence point of the titration is within. Or else the indicator would not indicate anything.

An example of indicators would be:
Phenolphthalein, pH range 8.3 - 10.0, is used for titrations with strong bases
Methyl orange. pH range 3.1 - 4.4, is used for titrations with strong acids