Acids, Bases And Buffers

Question 1

Write the equation for the dissociation of water

Answer 1

Question 2

Why does water have a pH of 7

Answer 2

Only source of hydrogen/ hydroxide ions is from water so [ hydrogen ions]=[ hydroxide ions]

Question 3

How do you calculate pH

Answer 3

Question 4

What does a buffer do

Answer 4

Resists ranges in pH upon the addition of a small amount of acids/base

Question 5

Write the equation (using displayed formula) for the deprotonation of ethanoic acid

Answer 5

Question 6

Write the general equation for the dissociation of an acid

Answer 6

Question 7

How do you calculate Ka

Answer 7

Question 8

What is the Henderson- hasselbach equation

Answer 8

Question 9

What does it mean if pH=pKa

Answer 9

Question 10

How do you calculate the ph of water using the Kw expression

Answer 10

Kw = 10^-14
Concentration of base would be given
Substitute conc. Of base into Kw expression
Kw\concentration of base=conc. of H+
- log [H+]= pH

Question 11

What does HA and A- mean

Answer 11

A- is the negative ion formed from the dissociation of the acid
HA is the acid in its normal protonated form

Question 12

What is the equation for the dissociation of a base

Answer 12

Question 13

What is the Henderson- hasselbach equation to find the ph of a base

Answer 13

Question 14

What is the general shape titration curve for a strong acne and strong base

Answer 14

Question 15

What is the general shape for the titration curve of a strong base with a weak acid

Answer 15

Question 16

How does a weak acid - string base buffer work

Answer 16

As base is added →reacts with protons so more acid is dissociated to replace the protons that were used
If more acid is added → equilibrium shifts to the left forming more acid

Question 17

What occurs at the equivalence point

Answer 17

pH = pKa
[A-]=[HA]

Question 18

What happens in the buffering period

Answer 18

Buffer would change by +/- 1 pH unit

Question 19

what does ‘pH is independent of dilution mean ‘

Answer 19

Question 20

Why does phosphoric acid have multiple pKa’s

Answer 20

Because it can undergo multiple dissociations

Question 21

What is the general shape of a phosphoric acid titration curve plus the corresponding dissociations occluding at each buffering period (+ the pKa at each dissociation)

Answer 21

Question 22

What does a small pKa mean

Answer 22

The smaller the pKa the stronger the acid (so it will dissociate more strongly)

Question 23

What can a strong acid do

Answer 23

Dissociate fully in water

Question 24

What is the bronsted Lowry definition of an acid and base

Answer 24

Question 25

What is the Arrhenius definition for an acid /base

Answer 25

Question 26

What is the general equation for an acid-base reaction

Answer 26

Question 27

What happens when acid is added to a buffer

Answer 27

1. Conc. Of H3O+ increases
2. Equilibrium shifts to the left to counteract change 3. H30+ combine with conjugate base (A-)to form more acid

Question 28

What happens when base is added to a buffer

Answer 28

1. OH- reacts with acid → produces salt and water (neutralisation reaction)
2. Salt dissociates to produce more A-

Question 29

Why is a strong acid /base not used to produce a buffer

Answer 29

Their equilibrium position lies far to the right
The backwards reaction rarely occurs (so strong acid/base wouldn’t di)ssociate

Question 30

How do acids / bases behave in aqueous solution + what is the general equation for the reaction of bases in water

Answer 30

Question 31

How would you find the ratio of [HA]/[A-]

Answer 31

Ratio of [A-]/[HA] found using Henderson hasselbach
1/[A-]/[HA]