acids 2

Question 1

adding small volume of acid

Answer 1

1- H+ reacts with A- to form HA

2- moves equilibrium to LHS

3- H+ that is added is removed to restore (H+)–> square brackets

4- (H+) only changes a small amount

5- PH only changes a small amount

Question 2

adding small volume of alkali

Answer 2

1- OH- reacts with H+ to form H20

2- more HA dissociates to restore (H+)

3- equilibrium moves to RHS

4- (H+) only changes a small amount

5- PH only changes a small amount

Question 3

buffer equation

Answer 3

Question 4

key equations

Answer 4

Question 5

Acid

Answer 5

H+ donor

Question 6

Base

Answer 6

H+ acceptor

Question 7

alkali

Answer 7

oh- donor

Question 8

conjugate acid

Answer 8

species after a base accepts proton - gains proton from original

Question 9

Conj base

Answer 9

species formed when acid donotes proton- loses proton from original

Question 10

Kw value

Answer 10

1x10-14

Question 11

Define a buffer system

Answer 11

A system that minimises pH changes on addition of small amounts of an acid or a base

Question 12

What assumptions are made when determining the pH of weak acids

Answer 12

1- [HA] in equilibrium = [HA] undissociated (inital)
–> dissociation of HA is negligible (weak acids don’t contribute much to dissociation )

2- [H+] in equilibrium = [A-]
–> as there is negligible dissociation of water (water hardly dissociates so will contribute very little H+ ions)

Question 13

What is the limitation with the assumptions made when calculating the pH of weak acids

Answer 13

With ‘stronger’ weak acids, [HA] in equilibrium = [HA] undissociated may no longer be valid

[H+] in equilibrium = [A-]

invalid at very dilute (H+ from water is not negliable)

Question 14

What is the equation for the buffer system in our blood

Answer 14

Question 15

What does the buffer system of our blood ensure

Answer 15

pH range is between 7.35 and 7.45

Question 16

How would the pH of a buffer solution change if the volume changes

Answer 16

pH remains the same
As the ratio of HA / A- remains the same

Question 17

What is the equivalence point on a pH graph

Answer 17

The volume of alkali added at the vertical line

Question 18

What is true at the equivalence point on a pH graph

Answer 18

mol Acid = mol Base

Question 19

How to explain that an indicator is suitable

Answer 19

The vertical section matches the pH range where the colour change occurs

Question 20

How can pH be measured experimentally

Answer 20

Using a pH probe and a data logger

Question 21

How can an aqueous solution of an acid contain hydroxide ions

Answer 21

water dissocites
- equation

Question 22

HNO2

Answer 22

weak acid

Question 23

body temp means

Answer 23

neutral

Question 24

neutral defintion

Answer 24

OH = H+

Question 25

if Ka is bigger is it a weak or stronger acid

Answer 25

stronger acid

Question 26

AS KP decreases

Answer 26

eqiubrium further to LHS less dissociation weaker acid Pka increases

Question 27

If PKa lower

Answer 27

more acidic

Question 28

Answer 28

Moles of HA= 0.150 mol HB: Moles of HB 0.135  mol total moles = o.285 ( as strong acids fully dissociate) o.285/0/07 = 4.1 conc

Question 29

Answer 29

% diss = H+ conc/ Ch4Coh x100

Question 30

Ph curve

Answer 30

Question 31

pure water

Answer 31

H+ = OH- neutral (not to do with 7)

Question 32

How to explain the colour of an indicator at end point

Answer 32

Moles of HA = Moles of A- So final colour is a mix of the other colours