Hi can i please have some help thanks ?

enter image source here

1 Answer
May 15, 2018

(a) acidic solutions #ul("form"(bb"X"))#; (b) neutral solutions #ul("form"(bb"Z"))#; (c) alkaline solutions #ul("form"(bb"Y"))#

Indicators are compounds that have different colours depending on the pH of the solution.

Many indicators are weak acids in which the acid and base forms have different colours.

For example, we could write the equilibrium for phenolphthalein as

#underbrace("HIn")_color(red)("acid form colourless") + "H"_2"O" ⇌ underbrace(color(red)("In"^"-"))_color(red)("base form red") + "H"_3"O"^"+"#

The cyanidins have three forms: acid, neutral, and base.

We could write the equations for their equilibria as

#underbrace(color(red)("H"_2"In"^"+"))_color(red)("acid form red") stackrelcolor(blue)("-H"^"+")(color(white)(l)⇌) underbrace(color(purple)("HIn"))_color(purple)("neutral form purple")stackrelcolor(blue)("-H"^"+")(color(white)(l)⇌) underbrace(color(green)("In"^"-"))_color(green)("base form green")#
#color(white)(mmmmm)stackrelcolor(blue)("+H"^"+")()color(white)(mmmmmmml)stackrelcolor(blue)("+H"^"+")#

The points to note are:

  1. The neutral form has no charge
  2. The acidic form has one more proton, i.e. a positive charge
  3. The basic structure has one less proton, i.e. a negative charge

Thus, the equilibria are

equilibria