acids and bases part 2 Flashcards
what is added in an acid-base titration
a solution of a base of known concentration from a burette, to a measured amount of acid
what is used to find the end point in acid-titration
an indicator
how can the concentration of the acid be calculated in an acid base titration
from the volume of base required
what is a titration curve
a plot of pH against volume of base added
how is the pH measured
pH meter
what does the shape of a titration curve depend on
the strength of the acid and base used
key features of titration curve: strong acid and strong base
- low starting pH
- long vertical sector
- high end pH
key features of titration curve: strong acid weak base
- low starting pH
- shorter vertical sector
- lower end pH
key features of titration curve: weak acid and strong base
- higher starting pH
- shorter vertical sector
- high end pH
pH at equivalence point: strong acid and strong base
7
pH at equivalence point: strong acid weak base
5
pH at equivalence point: weak acid strong base
9.5
equivalence point
the point at which the acid and base are in the correct molar ratio
an indicator for an acid base titration
weak acid (HIn)
why do different indicators change colour at different pH values
they have different Ka values
when is the end point of a titration
the point at which the indicator changes colour
for a successful titration, which two points must correspond
equivalence and end point- so that indicator changes sharply at equivalence point
what must the pH range of the chosen indicator correspond to
the region of rapid pH change (vertical portion of pH curve)
buffer
a solution that maintains an approximately constant pH on addition of small amounts of acid/base
applications of buffers
shampoos and biological washing powder
what is an acidic buffer a mixture of
a weak acid and one of its salts
what does an acidic buffer maintain a pH of
below 7
in what two ways can an acidic buffer be made
add together HA and its salt, A-
partly neutralise HA with NaOH
buffer action (HA>
A- reacts with added H+ to create HA
equilibrium shifts to left hand side
