What is an indicator
An indicator is a molecular substance that changes colour as the pH of a
solution change
indicator made from?
weak acid or weak bases and its conjugate base/conjugate acid
What happens when indicator added to acidic solution
LCP
When indicator is added to an acidic solution (increase H3O+), equilibrium
shift to the left, favouring the acid form of the indicator, the observed
colour is that of HInd
What happens when basic indicator added to basic solution
LCP
When a basic indicator is added to a basic solution (decrease in
[H3O+] high pH), the equilibrium shifts to the right, favouring the base form of the indicator (Ind⁻), so the observed colour is that of Ind⁻
What is an equivalence point
point during neutralisation when acid and base are in the stoichiometric ratio of the reaction equation
Point at which equal moles of OH - and H+ are reacted.
What should the indicator cover (range)
Indicator selection is based upon the indicator range such that the range is
covers the equivalence point of titration
Name a acid indicator
Methylorange
methylred
What is methylorange ph range and it colours
3.1 to 4.4
<3.1 is red
>4.4 is yellow
centre is orange
what is methylred ph range and its colours
4.4 - 6.2
< 4.4 red
>6.2 yellow
centre is orange
what are some basic indicators
phenolphthalein
what is phenolphthalein ph range and its colours
8.3 to 10
<8.3 is colourless
>10 is pink
centre is pink
What is a neutral indicator
Bromothymol blue
what is ph range of bromothymol blue and its colours
6 - 7.6
yellow to blue
why indicator of bromocresol of ph range of 3.8 to 5.4 best for titration with eq point of around 5
- the indicator changes colour in the ph range of the equivalence point
- this indicator is the only indicator in that range
- the chaneg in colour of the indicator indicates that equivalence point has been reached.
