Chemistry: Acids and Bases Part 2
This flashcard set explains the steps and principles of acid-base titration, including the addition of a base from a burette, use of indicators to find the endpoint, and calculation of acid concentration from volume data. It introduces titration curves as pH vs. volume plots and highlights how their shape depends on the strength of the acid and base involved.
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
Key Terms
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
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| Term | Definition |
|---|---|
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 |
| 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 |
| 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 |
|
key features of titration curve: strong acid weak base |
|
key features of titration curve: weak acid and strong base |
|
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 |
buffer action (HA> | OH- reacts with H+ to create H2O- equilibrium shifts to RHS |
what concentrations are much greater in buffer solutions | [HA] and [A-] much greater than [H+] |
what does the pH of a buffer solution depend on | the Ka of the acid and the [HA]:[A-] |
how to work out [H+] in a buffer solution | Ka[HA]/[A-] |
why doesn't volume need to be taken into account in buffer solution calculations | cancel eachother out |
the buffer range | the range of pH values which a buffer solution using a particular weak acid can have |
what is the buffer range usually for a weak acid | pKa +/- 1 |
Required practical: pipette 25.0 cm3 of the… | Acid into a tall form beaker and add a few drops of the appropriate indicator |
Required practical: place the tall form beaker on top of a | Magnetic stirrer and place the magnet in the beaker |
Required practical: fill the bursts with | The base |
Required practical: rinse the electrode with distilled water and dip it into the acid in the | Beaker |
Required practical: record the pH in a | Results table |
Required practical: results table should include | pH of solution and colour of indicator |
Required practical: switch on the stirrer and make sure | That the magnet doesn’t strike the electrode when in position |
Add 5cm of the | Base from the burette and note both the pH and the indicator colour |
Required practical: continue adding the base, taking readings every | 5cm3 intervals for first 20cm3 Then every 1cm3 until 23.0cm3 Around equivalence you should add base in 0.5cm3 portions Return to 1cm3 portions until 30.0cm3 Then 5cm3 portions until 50.0cm3 base added |
Required practical: plot a graph of pH against | Volume of base added |