BST 121-3 General Chemistry – Bachelor of Biosystems Technology
Faculty of Technological Studies Uva Wellassa
UniversityBST 121-3
Experiment 3 - Extraction of pH indicators from Plant Materials and Characterization of
their color changes using a pH meter
Prelab Activity
1. Bring red cabbage (Blaukraut/purple-leaved varieties of Brassica oleracea) or Nil katarolu
flowers (Clitoria ternatea) to the laboratory
1. Theory
Refer to the following details given about a few indicators
Litmus
Litmus is a weak acid. It has a seriously complicated molecule which we will simplify to HLit.
The "H" is the proton that can be given away to something else. The "Lit" is the rest of the weak
acid molecule.
There will be an equilibrium established when this acid dissolves in water. Taking the simplified
version of this equilibrium:
The un-ionized litmus is red, whereas the ion is blue.
Now use Le Chatelier's Principle to work out what would happen if you added hydroxide ions or
some more hydrogen ions to this equilibrium.
Adding hydroxide ions:
Experiment 3
1
, BST 121-3 General Chemistry – Bachelor of Biosystems Technology
Adding Hydrogen ions:
Experiment 3
2
Faculty of Technological Studies Uva Wellassa
UniversityBST 121-3
Experiment 3 - Extraction of pH indicators from Plant Materials and Characterization of
their color changes using a pH meter
Prelab Activity
1. Bring red cabbage (Blaukraut/purple-leaved varieties of Brassica oleracea) or Nil katarolu
flowers (Clitoria ternatea) to the laboratory
1. Theory
Refer to the following details given about a few indicators
Litmus
Litmus is a weak acid. It has a seriously complicated molecule which we will simplify to HLit.
The "H" is the proton that can be given away to something else. The "Lit" is the rest of the weak
acid molecule.
There will be an equilibrium established when this acid dissolves in water. Taking the simplified
version of this equilibrium:
The un-ionized litmus is red, whereas the ion is blue.
Now use Le Chatelier's Principle to work out what would happen if you added hydroxide ions or
some more hydrogen ions to this equilibrium.
Adding hydroxide ions:
Experiment 3
1
, BST 121-3 General Chemistry – Bachelor of Biosystems Technology
Adding Hydrogen ions:
Experiment 3
2
