14B.3

Question 1

with weak acids titrated against strong base what happens at the beginning of the graph

Answer 1

a small but sharp increase before the buffer region

Question 2

what is the buffer range

Answer 2

the area in titration curve where change in pH is small and there is a considerable con of acid and base molecules

Question 3

how do we find the pKa value form a titration graph

Answer 3

find the half equivalent point then find the corresponding value of the pH at the equivalent point, the use that pH = pKa to find Ka since at half-equivalent point acid and salt equal each other so the eq of pH = Pka + log salt/base can be written as pH = pKa + 0

Question 4

how do we plot a titration graph

Answer 4

titrate a base against an acid after each addition of the base measure the pH of the solution then plot a pH against volume of base graph

Question 5

how can we find Ka using the half-volume method

Answer 5

1. using a volumetric pipette measure 25 cm of a weak acid into a conical flask
2. add a few drops of phenolphthalein indicator
3. titrate against a solution of aqueous sodium hydroxide until the end point colour change
4. note the volume of the sodium hydroxide, this is the minimum volume required to react completely with the acid
5. use another 25 cm of weak acid and titrate it against the same solution of sodium hydroxide, this time don’t add any indicator
6. only add half the volume of sodium hydroxide required to react with the acid
7. measure the pH of the solution which will equal the pKa