Unit 13: Assignment 1
A: Investigate acid-base equilibria in order and to understand buffer action to optimise acid-
base titration procedures.
1. Acid & Base Strength - calculations to demonstrate understanding of acid / base / buffer
strength.
, 4. Indicators - titration practical work to determine the selection of an indicator.
Colour Changes
Many indicators can be used in acid base titrations. For example, litmus Is a weak acid where
the H proton is given away to something else, an equilibrium is also made when this acid
dissolves in water. The equilibrium moves to replace the lost hydrogen ions, and when
hydrogen is added, the equilibrium moves and the extra hydrogen ions are removed, turning
red. The concentrations of the two colours will also become equal and a purple colour can be
observed.
For Litmus, the 50/50 occurs at a pH of near 7 and litmus is therefore, predominantly used to
test for acids and alkalis.
HLit (aq) H+(aq) + Lit-(aq) The Ionised litmus is red and the ion is blue.
Another commonly used indicator used for titrations is a weak acid called phenolphthalein,
this acid is colourless whereas the ion is vibrant pink. When hydrogen ion is added, the
equilibrium shifts to the left and the indicator turns colourless, whereas adding hydroxide
ions will remove the hydrogen ions from the equilibrium and replaces them, therefore turning
the indicator pink.
H-phph(aq) H+(aq) +. Phph-(aq)
Methyl orange is another indicator used for titration. It turns yellow in an alkaline solution
with this structure. When an acid is added, the structure of methyl orange in ana alkaline will
sightly change and a hydrogen ion is attached to a nitrogen and a positive charge will be
given to a nitrogen.
A: Investigate acid-base equilibria in order and to understand buffer action to optimise acid-
base titration procedures.
1. Acid & Base Strength - calculations to demonstrate understanding of acid / base / buffer
strength.
, 4. Indicators - titration practical work to determine the selection of an indicator.
Colour Changes
Many indicators can be used in acid base titrations. For example, litmus Is a weak acid where
the H proton is given away to something else, an equilibrium is also made when this acid
dissolves in water. The equilibrium moves to replace the lost hydrogen ions, and when
hydrogen is added, the equilibrium moves and the extra hydrogen ions are removed, turning
red. The concentrations of the two colours will also become equal and a purple colour can be
observed.
For Litmus, the 50/50 occurs at a pH of near 7 and litmus is therefore, predominantly used to
test for acids and alkalis.
HLit (aq) H+(aq) + Lit-(aq) The Ionised litmus is red and the ion is blue.
Another commonly used indicator used for titrations is a weak acid called phenolphthalein,
this acid is colourless whereas the ion is vibrant pink. When hydrogen ion is added, the
equilibrium shifts to the left and the indicator turns colourless, whereas adding hydroxide
ions will remove the hydrogen ions from the equilibrium and replaces them, therefore turning
the indicator pink.
H-phph(aq) H+(aq) +. Phph-(aq)
Methyl orange is another indicator used for titration. It turns yellow in an alkaline solution
with this structure. When an acid is added, the structure of methyl orange in ana alkaline will
sightly change and a hydrogen ion is attached to a nitrogen and a positive charge will be
given to a nitrogen.
