pH and buffer

Question 1

to calculate pH at the half equivalence point

Answer 1

at the half equivalence point, ka =[H+] so the pH at the half equivalence point = -log [ka]

Question 2

pH before at the beginning

Answer 2

use the molarity given to create an ICE table. If the initial is a base and Kb is used, subtract the pOH gotten from 14 to get pH

Question 3

pH at buffer region

Answer 3

1. find the moles at the beginning
2. find the moles added
3. find the moles left = moles at beginning - moles added
4. find molarity added
5. find molarity left
6. place in K equation and solve for [OH-] or [H+]

Question 4

pH at equivalence point

Answer 4

1. calculate moles at the beginning
2. moles of reactant = moles of conjugate product
3. find molarity of conjugate product by dividing moles of conjugate product by total volume
4. use conjugate product molarity to create an ICE table and find pH or pOH

Question 5

pH after equivalence

Answer 5

1. find moles at the beginning
2. find moles added
3. find moles left by substracting moles beginning from moles added.
4. find molarity by dividing moles left by total volume
5. use molarity to find pH

Question 6

buffer

Answer 6

resists pH change and is made by an acid/base and the salt of its conjugate.

Question 7

buffering capacity

Answer 7

the effectiveness of the buffer to resist pH change. The larger the amount of acid and its conjugate, the greater the capacity

Question 8

to calculate the pH of a buffer

Answer 8

use henderson-hasselbalch equation

pH = pKa + log ([A] / [HA])

Question 9

to calculate pH of a buffer when a strong acid/base is added

Answer 9

1. calculate the inital moles of the all reactants and the substance added
2. insert the initial moles in an ICE table.
3. change is the moles of substance added
4. get equilibrium and then divide by total volume to get molarity
5. solve for k
6. get pH

reference: lec 6 pages 49-59